Internet Standards/CD2.mdf/ccitt/1992/x/x226.asc

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Recommendation X.226

           PRESENTATION PROTOCOL SPECIFICATION FOR OPEN

          SYSTEMS INTERCONNECTION FOR CCITT APPLICATIONS1

                         (Melbourne, 1988)

     The CCITT,

considering

     (a)   that Recommendation X.200 defines the Reference Model of
Open System Interconnection for CCITT Applications;

      (b)    that  Recommendation X.208 specifies  Abstract  Syntax
Notation  One (ASN.1) for the specification of the Abstract  Syntax
of Protocols;

      (c)    that Recommendation X.209 specifies the Basic Encoding
Rules for Abstract Syntax Notation One;

      (d)    that  Recommendation X.210  defines  the  Open  Syntax
Interconnection (OSI) Layer Service Definition Conventions;

      (e)    that Recommendation X.215 defines the Session  Service
Definition for Open Systems Interconnection for CCITT Applications;

      (f)    that  Recommendation  X.216 defines  the  Presentation
Service  Definition  for  Open Systems  Interconnection  for  CCITT
Applications;

      (g)    that Recommendation X.410-1984 specifies the  protocol
for  Remote  Operation  and Reliable Transfer  Server  for  Message
Handling Systems,

unanimously declares

      that this Recommendation defines the Presentation Protocol of
Open Systems Interconnection for CCITT Applications as given in the
Scope and Field of Application.

                             CONTENTS

0    Introduction

1    Scope and field of application

2    References

3    Definitions

     3.1   Reference Model definitions

     3.2   Service convention definitions

     3.3   Naming and Addressing definitions

     3.4   Presentation Service definitions

     3.5   Presentation protocol definitions

4    Abbreviations

     4.1   Data Units

     4.2   Types of presentation-protocol-data-units

     4.3   Other abbreviations

5    Overview of the presentation protocol

     5.1   Service provided by the Presentation Layer

     5.2   Service assumed from the Session Layer

     5.3   Functions of the Presentation Layer

     5.4   Presentation functional units

     5.5   Model of the Presentation Layer

6    Elements of procedure

     6.1   User data parameters

     6.2   Connection establishment

     6.3   Normal release of connection

     6.4   Abnormal release of connection

     6.5   Context Alteration

     6.6   Information transfer

     6.7   Token handling

     6.8   Synchronization and resynchronization

     6.9   Exception reporting

     6.10  Activity management

7    Mapping of PPDUS onto the session-service

     7.1   Connection establishment

     7.2   Normal release of connection

     7.3   Abnormal release of connection

     7.4   Context Alteration

     7.5   Information Transfer

     7.6   Token Handling

     7.7   Synchronization

     7.8   Resynchronization

     7.9   Exception Reporting

     7.10  Activity Management

8    Structure and encoding of PPDUS

     8.1   General

     8.2   Structure of SS-user data parameter values

     8.3   Encoding of SS-user data parameter values

     8.4   Encoding of values of type User-data

     8.5   Rules of extensibility for normal mode

9    Conformance

     9.1   Dynamic Conformance

     9.2   Static Conformance

     9.3   Protocol implementation conformance statement

Annex A - State tables

Appendix  I  -  Differences between Recommendation  X.226  and  ISO
International Standard 8823

0    Introduction

      This  Recommendation  is  one of  a  set  of  Recommendations
produced   to   facilitate  the  interconnection   of   information
processing systems. It is related to other Recommendations  in  the
set   as   defined  by  the  Reference  Model  for   Open   Systems
Interconnection   (Recommendation  X.200).  The   Reference   Model
subdivides the area of standardization for interconnection  into  a
series of layers of specification, each of manageable size.

      This  Recommendation specifies a common encoding and a number
of  functional units of presentation protocol procedures to be used
to  meet  the  needs of presentation-service-users. It is  intended
that  the presentation protocol should be simple but general enough
to  cater  for  the total range of presentation-service-user  needs
without restricting future extensions.

      The primary aim of this Recommendation is to provide a set of
rules for communication expressed in terms of the procedures to  be
carried  out  by peer entities at the time of communication.  These
rules  for communication are intended to provide a sound basis  for
development in order to serve a variety of purposes:

     a) as a guide for implementors and designers;

     b) for use in the testing and procurement of equipment;

      c) as part of an agreement for the admittance of systems into
the open systems environment;

     d) as a refinement of the understanding of OSI.

      It  is expected that the inifial users of this Recommendation
will  be  designers and implementors of equipment and therefore  it
contains, in notes or in annexes, guidance on the implementation of
its procedures.

      It has not been possible as yet to prepare a product standard
containing  a  set  of  objective tests  for  conformance  to  this
Recommendation  but  it does contain a section  on  conformance  of
equipment  claiming  to  implement  the  procedures  it  specifies.
Attention  is drawn to the fact that this Recommendation  does  not
contain  any  test  to  demonstrate this  conformance  and  cannot,
therefore, be considered as a complete product standard.

       The   variations   and   options   available   within   this
Recommendation are essential to enable a presentation-service to be
provided  for  a  wide variety of applications. Thus,  a  minimally
conforming  implementation will not be  suitable  for  use  in  all
possible circumstances. It is necessary, therefore, to qualify  all
references  to this Recommendation with statements of  the  options
provided or required, or with statements of the intended purpose of
provision or use.

1    Scope and field of application2

1.1  This Recommendation specifies:

     a) procedures for the transfer of data and control information
from one presentation-entity to a peer presentation-entity;

      b)  the means of selecting, by means of functional units, the
procedures to be used by the presentation-entities;

      c)  the  structure and encoding of the presentation-protocol-
data-units used for the transfer of data and control information.

     The procedures are defined in terms of:

     d) the interactions between peer presentation-entities through
the exchange of presentation-protocol-data-units;

      e)  the  interactions between a presentation-entity  and  the
presentation-service-user in the same system through  the  exchange
of presentation-service primitives;

      f)  the  interactions between a presentation-entity  and  the
session-service-provider  through the exchange  of  session-service
primitives.

1.2   These  procedures  are  defined in  the  main  text  of  this
Recommendation supplemented by state tables in annex A.

1.3   These procedures are applicable to instances of communication
between  systems which support the Presentation Layer  of  the  OSI
Reference  Model  and  which  wish  to  interconnect  in   an   OSI
environment.

1.4   This  Recommendation also specifies conformance criteria  for
systems  implementing these procedures. It does not  contain  tests
which can be used to demonstrate this conformance.

2    References

      Recommendation X.200     -    Reference Model of Open Systems
Interconnection for CCITT Applications. (See also ISO 7498).

      Recommendation  X.210     -    OSI Layer  Service  Definition
Conventions (see also ISO TR 8509).

      ISO  7498-3      -    Information processing systems  -  Open
Systems  Interconnection - basic Reference Model - Part  3:  Naming
and Addressing3.

      Recommendation X.215     -    Session Service Definition  for
Open  Systems Interconnection for CCITT Applications (see also  ISO
8326 and ISO 8326 addendum 2).

     Recommendation X.208     -    Specification of Abstract Syntax
Notation One (ASN.1) for CCITT Applications (see also ISO 8824).

      Recommendation X.209     -    Specification of Basic Encoding
Rules for Abstract Syntax Notation One. (See also ISO 8825).

      Recommendation X.216     -    Presentation Service Definition
for  Open Systems Interconnection for CCITT Applications (see  also
ISO 8822).

      Recommendation  X.410-1984      -     1984  Message  Handling
Systems: Remote Operation and Reliable Transfer Server.

3    Definitions

3.1  Reference Model definitions

      This  Recommendation  is based on the concepts  developed  in
Recommendation X.200 and makes use of the following  terms  derived
from it:

     a) presentation-connection;

     b) Presentation Layer;

     c) presentation-protocol-data-unit;

     d) presentation-service;

     e) presentation-service-access-point;

     f) presentation-service-data-unit;

     g) presentation-protocol-control-information;

     h) session-connection;

     i) Session Layer;

     j) session-service-acces-point;

     k) session-service-data-unit;

     l) session-service-provider;

     m) transfer syntax.

3.2  Service conventions definitions

      This  Recommendation makes use of the following terms defined
in Recommendation X.210 as they apply in the Presentation Layer:

     a) service-user;

     b) service-provider;

     c) service primitive;

     d) request;

     e) indication;

     f) response;

     g) confirm;

     h) non-confirmed-service;

     i) confirmed-service;

     j) provider-initiated-service.

3.3  Naming and Addressing definitions

      This  Recommendation makes use of the following terms defined
in ISO 7498-3:

     a) session-address;

     b) presentation-address;

     c) presentation-selector.

3.4  Presentation Service definitions

      This  Recommendation is also based on concepts  developed  in
Recommendation X.216 and makes use of the following  terms  defined
in that Recommendation:

     a) abstract syntax;

     b) abstract syntax name;

     c) transfer syntax name;

     d) presentation data value;

     e) presentation context;

     f) defined context set;

     g) inter-activity defined context set;

     h) default conext;

     i) functional unit;

     j) X.410-1984 mode;

     k) normal mode.

3.5  Presentation protocol definitions

       For  the  purpose  of  this  Recommendation,  the  following
definitions apply:

3.5.1   Vlocal matterV

      A  decision made by a system concerning its behaviour in  the
Presentation Layer that is not subject to the requirements of  this
Recommendation.

3.5.2   valid presentation-protocol-data-unitV

      A  presentation-protocol-data-unit which  complies  with  the
requirements of this Recommendation for structure and encoding.

3.5.3   Vinvalid presentation-protocol-data-unitV

      A  presentation-protocol-data-unit which does not comply with
the requirements of this Recommendation for structure and encoding.

3.5.4   Vprotocol errorV

     A situation occuring when a presentation-protocol-data-unit is
used in a way which does not comply with the procedures defined  in
this Recommendation.

3.5.5   Voriginal activity identifierV

      An  attribute of an activity in progress. If the activity was
started  by  use  of  the  P-ACTIVITY-START service,  the  Activity
identifier  parameter value of the request and  indication  service
primitives;  if the activity was resumed by use of the  P-ACTIVITY-
RESUME  service the Old activity identifier parameter value of  the
request and indication service primitives.

3.5.6   Vself-delimitingV

     An attribute of a transfer syntax which indicates that the end
of each value in that syntax can be determined by means provided by
the syntax.

3.5.7   Vpresentation context identifierV

      An  identifier  for  a  specific  presentation  context.  The
identifier is unique within a presentation-connection and known  to
both  presentation protocol machines. The default context does  not
have a presentation context identifier associated with it.

3.5.8   Vsyncpoint identifierV

      A synchronization point serial number if the session activity
management  functional unit has not been selected;  or  a  pair  of
synchronization   point   serial  number  and   original   activity
identifier  of  the  activity in progress if the  session  activity
management  functional  unit  has  been  selected.  The  order   of
syncpoint   identifiers  is  defined  as   the   order   of   their
synchronization point serial number components.

3.5.9   VinitiatorV

       The   presentation  protocol  machine  that  initiates   the
presentation-connection establishment.

3.5.10  VresponderV

       The  presentation  protocol  machine  that  responds  to   a
presentation-connection establishment proposal.

3.5.11  VrequestorV

      The presentation protocol machine that initiates a particular
action.

3.5.12  VacceptorV

      The  presentation protocol machine that accepts a  particular
action.

4    Abbreviations

4.1  Data Units

     VPPDU presentation-protocol-data-unit

     VPSDU presentation-service-data-unit

     VSSDU session-service-data-unit

4.2  Types of presentation-protocol-data-units

     VAC PPDU  Alter Context PPDU

     VACA PPDU Alter Context Acknowledge PPDU

     VARP PPDU Abnormal Release Provider PPDU

     VARU PPDU Abnormal Release User PPDU

     VCP PPDU  Connect Presentation PPDU

     VCPA PPDU Connect Presentation Accept PPDU

     VCPR PPDU Connect Presentation Reject PPDU

     VRS PPDU  Resynchronize PPDU

     VRSA PPDU Resynchronize Acknowledge PPDU

     VTC PPDU  Capacility Data PPDU

     VTCC PPDU Capability Data Acknowledge PPDU

     VTD PPDU  Presentation Data PPDU

     VTE PPDU  Expedited Data PPDU

     VTTD PPDU Presentation typed Data PPDU

4.3  Other abbreviations

      VASN.1   Abstract  Syntax  Notation One  (see  Recommendation
X.208)

     VDCS  defined context set

     VPPCI presentation-protocol-control-information

     VPPM  presentation protocol machine

     VPS   presentation-service

     VPSAP presentation-service-access-point

     VPS-user  presentation-service-user

     VSS   session-service

     VSSAP session-service-access-point

5    Overview of the presentation protocol

5.1  Service provided by the Presentation Layer

      The  protocol specified in this Recommendation  supports  the
presentation-service defined in Recommendation X.216.

5.2  Service assumed from the Session Layer

      The protocol specified in this Recommendation assumes the use
of the session-service defined in Recommendation X.215.

5.3  Functions of the Presentation Layer

      The functions of the Presentation Layer are described in  the
Reference Model, Recommendation X.200, and are further expanded  in
the Presentation Service Definition, Recommendation X.216.

5.4  Presentation functional units

       Functional  units  are  logical  groupings  of  elements  of
procedure defined by this Recommendation for the purpose of:

      a)  negotiation during presentation-connection  establishment
for subsequent use on the presentation-connection;

     b) specification of conformance requirements.

      The  selection of the presentation functional units does  not
constrain the selection of session functional units to be available
to  the PS-user. Selection of a particular session functional  unit
to  be available to the PS-user implies the rules of interaction of
that  session functional unit with whatever presentation functional
units are selected, as pecified by this Recommendation.

5.4.1   Kernel functional unit

      This functional unit, which is always available, supports the
basic  protocol  elements  of procedure  required  to  establish  a
presentation-connection,   transfer   data,   and    release    the
presentation-connection.

      Note  -  This is the presentation kernel functional unit;  it
supports  data  transfer on whatever session functional  units  are
selected for those presentation-service primitives which allow User
data parameters.

5.4.2   Context management functional unit

      This  functional  unit  supports  the  context  addition  and
deletion services. This functional unit is optional, and its use is
negotiable.

5.4.3   Context restoration functional unit

     This functional unit adds further Presentation Layer functions
when the session activity management functional unit is selected or
when  both  the  session synchronization (major or minor)  and  the
session  resynchronization  functional  units  are  selected.   The
context  restoration functional unit is optional, and  its  use  is
negotiable;  it  is  available  only when  the  context  management
functional is selected.

5.5  Model of the Presentation Layer

      The presentation protocol machine (PPM), see the note, within
the  presentation-entity communicates with the  PS-user  through  a
PSAP by means of presentation-service primitives as defined by  the
Presentation    Service    Definition    (Recommendation    X.216).
Presentation-service primitives will cause  or  be  the  result  of
presentation-protocol-data-unit (PPDU) exchanges between  the  peer
PPMs  using  a  session-connection. These  protocol  exchanges  are
effected using the services of the Session Layer as defined by  the
Session  Service Definition (Recommendation X.215). In some  cases,
presentation-service  primitives will  directly  cause  or  be  the
result of session-service primitives.

       Presentation-connection-endpoints  are  identified  in   end
systems by an internal, implementation dependent, mechanism so that
the   PS-user  and  the  presentation-entity  can  refer  to   each
presentation-connection.

      The  reception of a service primitive and the  generation  of
dependent  actions are considered to be an indivisible action.  The
reception  of  a PPDU and the generation of dependent  actions  are
considered to be an indivisible action.

     The model of the Presentation Layer for a single presentation-
connection is illustrated in Figure 1/X.226.

     Note - A presentation entity is comprised of one or more PPMs.




                          Figure 1/X.226

6    Elements of procedure

     For the purpose of description, this specification of elements
of procedure employs an integrated treatment of PPDU parameters and
session-service  primitive  parameters.  This  section   does   not
identity  a  parameter  as either a PPDU parameter  or  a  session-
service primitive parameter. Such a distinction is specified  in  ñ
7.  For further information on the use of parameters, refer to  the
Presentation Service Definition (Recommendation X.216).

6.1  User data parameters

      Most  of the PPDUs used in the procedures of the presentation
protocol  carry  User  data  parameters  containing  one  or   more
presentation  data values. The remainder of the section  gives  the
rules  for  determining the presentation contexts from which  these
presentation data values (including any embedded presentation  data
values) shall be taken.

      Note  - If the underlying session-service-provider imposes  a
restriction  on the length of certain SS-user data parameters,  the
PPM  shall  reject  any presentation-service  request  or  response
primitive (with the exception of a P-U-ABORT request primitive, see
ñ  6.4.2.2) carrying a User data parameter which does not fit  into
the  SS-user  data  parameter of the corresponding  session-service
primitive.  The way in which the PPM is made aware  of  this  is  a
local matter.

6.1.1    The  presentation  data  values  (including  any  embedded
presentation data values) which may be transferred in the User data
parameter of the TE PPDU shall always be from the default context.

6.1.2    The  presentation  data  values  (including  any  embedded
presentation data values) in User data parameters except for the TE
PPDU  shall  be  from  presentation  contexts  determined  by   the
following rules:

      a)  If  the  DCS is empty and (d) does not apply,  then  each
presentation  data value (including any embedded presentation  data
values) shall be from the default context.

      b)  If  the DCS is not empty and no procedure is in  progress
which  can  amend  the contents of the DCS, then each  presentation
data  value (including any embedded presentation data values) shall
be from a presentation context of the DCS.

      c)  If  the element of procedure itself amends the DCS,  then
each  presentation data value (including any embedded  presentation
data  values) shall be from a presentation context of the DCS which
results  from this amendment, or from the default context  if  this
amendment leaves the DCS empty.

      d)  If a PPM is awaiting a PPDU which will confirm a proposed
amendment  to the DCS, then each presentation data value (including
any embedded presentation data values) shall be from a presentation
context  of  the DCS which was not proposed for deletion  from  the
DCS.  If  this leaves no presentation contexts available, then  the
User data parameter shall not be present.

6.2  Connection establishment

6.2.1   Purpose

      The connection establishment procedure is used to establish a
presentation-connection  between two presentation-entities.  It  is
used  by  a  PPM  which  has received a P-CONNECT  request  service
primitive.

     The procedure uses the following PPDUs:

     a) CP PPDU;

     b) CPA PPDU;

     c) CPR PPDU.

6.2.2   CP PPDU associated parameters

6.2.2.1 Mode selector

      This  shall be the Mode parameter from the P-CONNECT  request
service primitive and shall identify the mode of operation  of  the
PPM  for this presentation-connection. It shall appear as the  Mode
parameter of the P-CONNECT indication service primitive, if issued.

6.2.2.2 Protocol version

      This shall identify each version of the presentation protocol
that  the  initiating  PPM supports. The version  of  the  protocol
defined in this Recommendation shall be version-1.

     See also ñ 6.2.6.4.

6.2.2.3 Calling-presentation-selector

      This  shall be the presentation-selector part of the Calling-
presentation-address parameter from the P-CONNECT  request  service
primitive  and  shall  appear  as the calling-presentation-selector
part of the Calling-presentation-address parameter of the P-CONNECT
indication service primitive, if issued.

6.2.2.4 Calling-session-address

      This  shall  be  the  session-address part  of  the  Calling-
presentation-address parameter from the P-CONNECT  request  service
primitive  and  shall  appear as the session-address  part  of  the
Calling-presentation-address parameter of the P-CONNECT  indication
service primitive, if issued.

6.2.2.5 Called-presentation-selector

      This  shall be the presentation-selector part of the  Called-
presentation-address parameter from the P-CONNECT  request  service
primitive and shall appear as the called-presentation-selector part
of  the  Called-  presentation-address parameter of  the  P-CONNECT
indication service primitive, if issued.

6.2.2.6 Called-session-address

      This  shall  be  the  session-address  part  of  the  Called-
presentation-address parameter from the P-CONNECT  request  service
primitive  and  shall  appear as the session-address  part  of  the
Called-presentation-address parameter of the  P-CONNECT  indication
service primitive, if issued.

6.2.2.7 Presentation context definition list

      This shall be a list containing one or more items. Each  item
represents  one  item of the Presentation context  definition  list
parameter  from the P-CONNECT request service primitive  and  shall
appear  as  one  item of the Presentation context  definition  list
parameter of the P-CONNECT indication service primitive, if issued.
Each   item  contains  three  components:  a  presentation  context
identifier, an abstract syntax name and a transfer syntax list.

      The transfer syntax list contains the names of those transfer
syntaxes  (or  the names of specifications producing such  transfer
syntaxes) that the initiating PPM is capable of supporting for  the
named abstract syntax on the presentation-connection (at least  one
transfer syntax name for each proposed presentation context).

       All  presentation  context  identifiers  contained  in  this
parameter shall be different and shall be odd integers.

     Note - The presentation context identifiers are specified here
to  be  odd integers so that they are chosen from a separate number
space  from those identifiers allocated by the responding PPM  (see
also ñ 6.5).

     See also ñ 6.2.6.1.

6.2.2.8 Default context name

      This shall be the Default context name parameter from the  P-
CONNECT  request service primitive and shall appear as the  Default
context   name  parameter  of  the  P-CONNECT  indication   service
primitive,  if  issued.  It contains two  components:  an  abstract
syntax  name  and  a  transfer  syntax  name  (or  the  name  of  a
specification  producing  such  a transfer  syntax).  The  transfer
syntax  name  component identifies the transfer syntax required  by
the  initiating  PPM for the default context  to  be  used  on  the
presentation-connection.

     See also ñ 6.2.6.2.

6.2.2.9 Quality of service

      This  shall be the Quality of service parameter from  the  P-
CONNECT  request service primitive and shall appear as the  Quality
of service parameter of the P-CONNECT indication service primitive,
if issued.

6.2.2.10   Presentation requirements

     This shall be the Presentation requirements parameter from the
P-CONNECT   request  service  primitive  and  shall  identify   the
presentation functional units proposed by the initiating PS-user in
the  P-CONNECT  request service primitive. It shall appear  as  the
Presentation  requirements parameter of  the  P-CONNECT  indication
service  primitive, if issued, unless the responding PPM  does  not
support  all  of  them, in which case only those  functional  units
supported by the responding PPM shall appear.

     See also ñ 6.2.6.3.

6.2.2.11   User session requirements

      This shall be the Session requirements parameter from the  P-
CONNECT   request   service  primitive  and  shall   identify   the
requirements to the underlying session-service proposed by the  PS-
user. It shall appear as the Session requirements parameter of  the
P-CONNECT indication service primitive, if issued.

6.2.2.12   Revised session requirements

      This shall be the Session requirements parameter from the  P-
CONNECT  request service primitive, supplemented by such additional
requirements as are needed to support the presentation protocol.

6.2.2.13   Initial synchronization point serial number

      This shall be the Initial synchronization point serial number
parameter  from the P-CONNECT request service primitive, and  shall
appear as the Initial synchronization point serial number parameter
of the P-CONNECT indication service primitive, if issued.

6.2.2.14   Initial assignment of tokens

      This shall be the Initial assignment of tokens parameter from
the  P-CONNECT request service primitive, and shall appear  as  the
Initial  assignment of tokens parameter of the P-CONNECT indication
service primitive, if issued.

6.2.2.15   Session connection identifier

     This shall be the Session connection identifier parameter from
the  P-CONNECT request service primitive, and shall appear  as  the
Session connection identifier parameter of the P-CONNECT indication
service primitive, if issued.

6.2.2.16   User data

      This  shall  represent the User data parameter  from  the  P-
CONNECT  request service primitive, and shall appear  as  the  User
data  parameter of the P-CONNECT indication service  primitive,  if
issued.  If  the Presentation context definition list parameter  is
not  present, then it shall be a list of presentation  data  values
(including any embedded presentation data values) from the  default
context.  Otherwise it shall be a list of presentation data  values
(including any embedded presentation data values) from presentation
contexts  proposed  in  the Presentation  context  definition  list
parameter.

6.2.3   CPA PPDU associated parameters

      An  instance  of a CPA PPDU need not contain values  for  all
possible  parameters;  in  addition to the Responding-presentation-
selector and Responding-session-address parameters, it should  only
contain  values for equivalent parameter value present  in  the  CP
PPDU for which it is a reply.

6.2.3.1 Mode selector

     This shall be the Mode selector parameter from the CP PPDU.

6.2.3.2 Protocol version

      This  shall identify the version of the presentation protocol
selected  for use on this presentation-connection. The  version  of
the protocol defined in this Recommendation shall be version-1.

6.2.3.3 Responding-presentation-selector

       This  shall  be  the  presentation-selection  part  of   the
Responding-presentation-address  parameter   from   the   P-CONNECT
response  service  primitive and shall appear  as  the  responding-
presentation-selector  part  of the Responding-presentation-address
parameter of the P-CONNECT confirm service primitive.

6.2.3.4 Responding-session-address

      This  shall  be  the session-address part of the  Responding-
presentation-address parameter from the P-CONNECT response  service
primitive  and  shall  appear as the session-address  part  of  the
Responding-presentation-address parameter of the P-CONNECT  confirm
service primitive.

     See also ñ 6.2.6.4.

6.2.3.5 Presentation context definition result list

      This  shall  represent  the Presentation  context  definition
result  list parameter of the P-CONNECT response service  primitive
and shall appear as the Presentation context definition result list
parameter  of the P-CONNECT confirm service primitive. It  consists
of  a  list containing the same number of items as the Presentation
context  definition list parameter of the CP PPDU. Each item  shall
be  a  reply to the corresponding item in the CP PPDU and  contains
one or two components, a presentation context definition result and
an  optional component which is either a transfer syntax  name  (or
the name of a specification producing such a transfer syntax) or  a
provider reason.

      The presentation context definition result shall take one  of
the values:

     -  ╥acceptance╙;

     -  ╥user-rejection╙;

     -  ╥provider rejection╙.

      The transfer syntax name shall be present if the presentation
context definition result takes the value ╥acceptance╙. It shall be
one  of  the  names  proposed  by the initiating  PPM  as  possible
transfer  syntaxes  for  the identified presentation  context,  and
shall  determine the transfer syntax which the responding  PPM  has
selected.

      The  provider  reason shall be present  if  the  presentation
context  definition  result component takes  the  value  ╥provider-
rejection╙.   It  specifies  the  reason  for  rejection   of   the
presentation  context definition by the responding  PPM  and  shall
take one of the values:

     -  reason not specified;

     -  abstract syntax requirements not supported;

     -  proposed transfer syntaxes not supported;

     -  local limit on DCS exceeded.

     See also ñ 6.2.6.1.

6.2.3.6 Quality of service

      This  shall be the Quality of service parameter from  the  P-
CONNECT  response service primitive and shall appear as the Quality
of service parameter of the P-CONNECT confirm service primitive.

6.2.3.7 Presentation requirements

     This shall be the Presentation requirements parameter from the
P-CONNECT  response  service primitive.  It  shall  appear  as  the
Presentation  requirements  parameter  of  the  P-CONNECT   confirm
service primitive.

     See also ñ 6.2.3.6.

6.2.3.8 User session requirements

      This shall be the Session requirements parameter from the  P-
CONNECT  response service primitive and shall appear as the Session
requirements parameter of the P-CONNECT confirm service primitive.

6.2.3.9 Revised session requirements

      This shall be the Session requirements parameter from the  P-
CONNECT response service primitive, supplemented by such additional
requirements as are needed to support the presentation protocol.

6.2.3.10   Initial synchronization point serial number

      This shall be the initial synchronization point serial number
parameter from the P-CONNECT response service primitive, and  shall
appear as the Initial synchronization point serial number parameter
of the P-CONNECT confirm service primitive.

6.2.3.11   Initial assignment of Tokens

      This shall be the Initial assignment of tokens parameter from
the  P-CONNECT response service primitive, and shall appear as  the
Initial  assignment  of tokens parameter of the  P-CONNECT  confirm
service primitive.

6.2.3.12   Session Connection Identifier

     This shall be the Session connection identifier parameter from
the  P-CONNECT response service primitive, and shall appear as  the
Session  connection identifier parameter of the  P-CONNECT  confirm
service primitive.

6.2.3.13   User data

      This  shall  be  the User data parameter from  the  P-CONNECT
response  service  primitive, and shall appear  as  the  User  data
parameter of the P-CONNECT confirm service primitive. The rules  of
$ 6.1.2 shall apply.

6.2.4   CPR PPDU associated parameters

      An  instance  of a CPR PPDU need not contain values  for  all
possible   parameters;   in   addition   to   presentation-selector
parameters   it   should  only  contain  values  for  corresponding
parameter values present in the CP PPDU for which it is a reply.

6.2.4.1 Protocol version

      This shall identify each version of the presentation protocol
that  the  responding  PPM supports. The version  of  the  protocol
defined in this Recommendation shall be version-1.

     See also ñ 6.2.6.4.

6.2.4.2 Responding-presentation-selector

     This shall be the presentation-selector part of the Responding-
presentation-address parameter from the P-CONNECT response  service
primitive  and shall appear as the responding-presentation-selector
part  of  the Responding-presentation-address parameter of  the  P-
CONNECT confirm service primitive.

6.2.4.3 Responding-session-address

      This  shall  be  the session-address part of the  Responding-
presentation-address parameter from the P-CONNECT response  service
primitive  and  shall  appear as the session-address  part  of  the
Responding-presentation-address parameter of the P-CONNECT  confirm
service primitive.

6.2.4.4 Presentation context definition result list

      This shall be the Presentation context definition result list
parameter  of  the P-CONNECT response service primitive  and  shall
appear as the Presentation context definition result list parameter
of  the P-CONNECT confirm service primitive. It consists of a  list
containing  the  same  number of items as the Presentation  context
definition  list  parameter of the CP PPDU. Each item  shall  be  a
reply to the corresponding item in the CP PPDU and contains one  or
two  components, a presentation context definition  result  and  an
optional component which is either a transfer syntax name  (or  the
name  of  a  specification producing such a transfer syntax)  or  a
provider reason.

     See also ñ 6.2.6.1.

      The presentation context definition result shall take one  of
the values:

     -  ╥acceptance╙;

     -  ╥user-rejection╙;

     -  ╥provider-rejection╙.

      The transfer syntax name shall be present if the presentation
context definition result takes the value ╥acceptance╙. It shall be
one  of  the  names  proposed  by the initiating  PPM  as  possible
transfer  syntaxes  for  the identified presentation  context,  and
shall  determine the transfer syntax which the responding  PPM  has
selected.

      The  provider  reason shall be present  if  the  presentation
context definition result takes the value ╥provider-rejection╙.  It
specifies  the  reason  for rejection of the  presentation  context
definition by the responding PPM and shall take one of the values:

     -  reason not specified;

     -  abstract syntaxt requirements not supported;

     -  proposed transfer syntaxes not supported;

     -  local limit on DCS exceeded.

6.2.4.5 Default context result

      This shall be the Default context result parameter of the  P-
CONNECT  response service primitive and shall appear as the Default
context   result   parameter  of  the  P-CONNECT  confirm   service
primitive. It may take the value ╥acceptance╙, ╥provider-rejection╙
or ╥user-rejection╙.

     See also ñ 6.2.6.2.

6.2.4.6 Quality of service

      This  shall be the Quality of service parameter from  the  P-
CONNECT response service primitive, or if the CPR PPDU is initiated
by  the responding PPM on receipt of a CP PPDU it shall be supplied
by  the  responding  PPM. In either case it  shall  appear  as  the
Quality  of  service  parameter of the  P-CONNECT  confirm  service
primitive. It shall identify a quality of service required  by  the
responding PS-user or presentation-service-provider.

6.2.4.7 Session requirements

      This shall be the Session requirements parameter from the  P-
CONNECT response service primitive, or if the CPR PPDU is initiated
by  the responding PPM on receipt of a CP PPDU it shall be supplied
by  the  responding  PPM. In either case it  shall  appear  as  the
Session  requirements  parameter of the P-CONNECT  confirm  service
primitive.  It  shall  identify  those  session  functional   units
required   by   the  responding  PS-user  or  presentation-service-
provider.

      Note  - If the presentation-connection establishment proposal
is  rejected  by  the PS-user, this parameter shall  represent  the
session  requirements of the PS-user as indicated in  the  response
primitive;  there is no Revised session requirements  parameter  in
this PPDU.

6.2.4.8 Session connection identifier

     This shall be the Session connection identifier parameter from
the  P-CONNECT response service primitive, and shall appear as  the
Session  connection identifier parameter of the  P-CONNECT  confirm
service primitive.

6.2.4.9 Provider reason

      If  present, this shall indicate that the rejection is by the
responding  presentation-service-provider; if  absent,  this  shall
indicate  that  the  rejection is by the responding  PS-user.  This
parameter  shall  indicate  the reason for  the  rejection  of  the
presentation-connection establishment proposal and shall appear  as
the  Provider  reason  parameter of the P-CONNECT  confirm  service
primitive. It shall take one of the following values:

     -  reason not specified (transient);

     -  temporary congestion (transient);

     -  local limit exceeded (permanent);

     -  called-presentation-address unknown (permanent);

     -  protocol version not supported (permanent);

     -  default context not supported (permanent);

     -  user data not readable (permanent);

      -   no PSAP available from the set of PSAPs identified by the
called-presentation-address (transient).

6.2.4.10   User data

      This  shall  be  the User data parameter from  the  P-CONNECT
response  service  primitive, and shall appear  as  the  User  data
parameter   of  the  P-CONNECT  confirm  service  primitive.   This
parameter  shall  contain  encodings of  presentation  data  values
(including  any  embedded presentation data values)  from  transfer
syntaxes  contained in the Presentation context  definition  result
list parameter of this CPR PPDU, if present, or otherwise according
to  the  default  context. It is not present if  the  presentation-
connection  establishment proposal is rejected by the presentation-
service-provider.

6.2.5   Procedure

6.2.5.1 When a P-CONNECT request service primitive is received by a
PPM  (the  initiator),  it shall initiate the  establishment  of  a
presentation-connection  by  sending  a  CP  PPDU  containing   the
presentation data values and proposed parameters necessary for  the
operation of the presentation-connection (see ñ 6.2.2).

6.2.5.2  As  an  initiator's option, the presentation  data  values
contained  in a CP PPDU may be encoded more than once to allow  the
transfer  of  the same presentation data values using a  number  of
different transfer syntaxes.

6.2.5.3 The responding PPM is not required to examine more than one
encoding  for each presentation data value received.  If,  for  any
presentation  data value received, all its examined  encodings  are
expressed  according  to transfer syntaxes  not  supported  by  the
responding  PPM, then the responding PPM shall refuse the  proposed
presentation-connection  by sending a  CPR  PPDU  with  a  Provider
reason parameter value of ╥user data not readable╙.

6.2.5.4 If the initiating PPM is unable to establish a presentation-
connection  due  to an inability to establish a session-connection,
it  shall issue a P-CONNECT confirm service primitive with a Result
parameter  value  of a ╥provider-rejection╙ and  the  presentation-
connection shall not be established.

6.2.5.5  The  responding PPM may refuse the proposed  presentation-
connection  (if, for example, the parameter values of the  CP  PPDU
are unacceptable; see also ñ 6.2.6), in which case it shall send  a
CPR  PPDU with a Provider reason parameter included (see ñ  6.2.4).
Alternatively,  if  not  refusing,  it  shall  issue  a   P-CONNECT
indication service primitive.

6.2.5.6  If  the responding PPM then receives a P-CONNECT  response
service   primitive  with  a  Result  parameter  value  of   ╥user-
rejection╙,  it  shall send a CPR PPDU (see ñ  6.2.4),  but  if  it
receives  a  P-CONNECT  response service primitive  with  a  Result
parameter  value of ╥acceptance╙, it shall send a CPA PPDU  (see  ñ
6.2.3).

6.2.5.7  If  the  initiating PPM receives  CPR  PPDU  refusing  the
presentation-connection, then it shall issue  a  P-CONNECT  confirm
service primitive with a Result parameter value of ╥user-rejection╙
(if  the  Provider reason parameter is not present)  or  ╥provider-
rejection╙ (if the Provider reason parameter is present),  and  the
presentation-connection shall not be established.

6.2.5.8  If  the initiating PPM receives a CPA PPDU  accepting  the
presentation-connection, then it shall issue  a  P-CONNECT  confirm
service  primitive with a Result parameter value  of  ╥acceptance╙,
and the presentation-connection shall be established.

6.2.5.9 If the presentation-connection is established, the  DCS  of
each PPM is set according to the parameters of the CPA PPDU.

6.2.6   Negotiation

6.2.6.1 Presentation context negotiation

        The    DCS    determined   during   presentation-connection
establishment is negotiated between the peer PPMs and the PS-users.

     The initiating PPM provides for each abstract syntax requested
by  its  PS-user  a  list of transfer syntaxes  it  is  capable  of
supporting  for  the  presentation-connection. The  responding  PPM
indicates in the P-CONNECT indication service primitive to its  PS-
user  those  abstract syntaxes it cannot support using one  of  the
proposed  transfer  syntaxes, marking them as  refused  (╥provider-
rejection╙).  The  responding  PS-user  indicates  those   abstract
syntaxes  it  accepts or refuses in the P-CONNECT response  service
primitive.  The  responding PPM selects one item  of  the  transfer
syntax  list as the transfer syntax to be used on the presentation-
connection for each accepted presentation context.

     A presentation context is identified by a presentation context
identifier provided by the initiating PPM.

6.2.6.2 Default context negotiation

     If the Default context name parameter is not present in the P-
CONNECT  request  service  primitive, then  the  interpretation  of
presentation data values from the default context is specified in a
manner which is outside the scope of this Recommendation.

      If  the  Default  context name parameter is present  and  the
responding PPM does not support the named default context, it shall
send  a CPR PPDU with a Provider reason parameter value of ╥default
context  not  supported╙ and a Default context result parameter  of
value ╥provider-rejection╙.

      If  the responding PPM supports the named default context but
receives  a  P-CONNECT response service primitive  with  a  Default
context  result parameter value of ╥user-rejection╙, then it  shall
send  a  CPR PPDU with a Default context result parameter of ╥user-
rejection╙.

6.2.6.3 Functional units negotiation

      Presentation functional units are negotiated between the  two
PS-users.  The  presentation  functional  units  selected  for  the
presentation-connection are those which are required  by  both  PS-
users  and  are supported by both PPMs. The negotiation of  session
functional  units  is subject to the rules of the  Session  Service
Definition (Recommendation X.215).

6.2.6.4 Protocol version negotiation

      Presentation protocol version is negotiated between  the  two
PPMs.

     In the CP PPDU, the initiating PPM provides a list of versions
that  it  is capable of supporting. In the CPA PPDU, the responding
PPM  indicates the version of the presentation protocol used on the
presentation-connection; this shall be one of the versions proposed
by  the  initiating  PPM. In the CPR PPDU, the responding  PPM  may
indicate  a list of versions that it is capable of supporting;  the
use of this list is a local matter.

6.2.7   Collisions and interactions

6.2.7.1 P-U-ABORT

      If  the  initiating PPM receives a P-U-ABORT request  service
primitive after it has sent a CP PPDU but before it has issued a P-
CONNECT  confirm service primitive, it shall send an ARU  PPDU  and
the presentation-connection shall not be established.

6.7.7.2 ARU PPDU, ARP PPDU and S-P-ABORT

     If the initiating PPM receives an S-P-ABORT indication service
primitive  or  an  ARP PPDU, it shall issue a P-P-ABORT  indication
service  primitive  and the presentation-connection  shall  not  be
established.

     If the initiating PPM receives an ARU PPDU, it shall issue a P-
U-ABORT   indication  service  primitive  and   the   presentation-
connection shall not be established.

     The responding PPM shall react to ARU PPDUs, ARP PPDUs and S-P-
ABORT indication service primitives as above, once it has issued  a
P-CONNECT indication service primitive.

6.3  Normal release of connection

6.3.1   Purpose

      The  procedure  for  the normal release  of  a  presentation-
connection  is used by a PPM to release the presentation-connection
without loss of data in transit.

6.3.2   Procedure

6.3.2.1  Normal release of the presentation-connection takes  place
concurrently with the release of the underlying session-connection.
PPDUs  are  not  explicitly defined, but implicitly  given  by  the
description of mapping in Section 7.

6.3.2.2  The SS-user data parameters of session-service  primitives
used  shall represent or be represented by the User data parameters
of the associated presentation-service primitives and shall be from
presentation contexts as specified in ñ 6.1.2.

6.4  Abnormal release of connection

6.4.1   Purpose

      The  procedure  for the abnormal release of  a  presentation-
connection  is  used  at  any time to  force  the  release  of  the
presentation-connection. It is invoked by the P-U-ABORT service  or
in  response  to a protocol error or the reception  of  an  invalid
PPDU.

     The procedure uses the following PPDUs:

     a) ARU PPDU;

     b) ARP PPDU.

6.4.2   ARU PPDU associated parameters

6.4.2.1 Presentation context identifier list

      This parameter shall be present if the User data parameter is
present  in  the ARU PPDU and if the context management  functional
unit  has  been selected, or if the Presentation context definition
list  parameter  was present in the CP PPDU. For each  presentation
context  used  in the ARU PPDU User data parameter, this  parameter
identifies the transfer syntax used.

      It  consists  of  a  list, each item of  which  contains  two
components,  a  presentation context identifier and  an  associated
transfer syntax name (or the name of a specification producing such
a transfer syntax).

     Note - If the DCS is empty, this parameter shall be empty.

6.4.2.2 User-data

      This  parameter shall represent the User data parameter  from
the P-U-ABORT request service primitive and shall be represented by
the  User  data  parameter  of  the  P-U-ABORT  indication  service
primitive.  The  parameter shall be from presentation  contexts  as
defined in ñ 6.1.2.

      Note  -  If the length restrictions imposed by the underlying
session-service  prevent  the inclusion of  the  presentation  data
values of the User data parameter in the SS-user data parameter  of
the  S-U-ABORT  request session-service primitive,  the  User  data
parameter  will not be included in the ARU PPDU sent.  The  way  in
which the PPM is made aware of this is a local matter.

6.4.3   ARP PPDU associated parameters

6.4.3.1 Provider Reason

     This parameter shall indicate one of the following reasons:

     a) reason not specified;

     b) unrecognized PPDU;

     c) unexpected PPDU;

     d) unexpected session-service primitive;

     e) unrecognized PPDU parameter;

     f) unexpected PPDU parameter;

     g) invalid PPDU parameter value.

     In cases c), d), e), f) and g), the Event identifier parameter
shall also be present.

6.4.3.2 Event identifier

      This parameter shall identify the PPDU or the session-service
primitive which triggered the abort procedure.

6.4.4   Procedure

     The procedure shall depend on the stimulus as follows:

6.4.4.1 P-U-ABORT

      When a PPM receives a P-U-ABORT request service primitive and
either:

     a) a presentation-connection has been established; or

      b)  a CP PPDU has been sent, and neither a CPA PPDU nor a CPR
PPDU has been received,

it  shall send an ARU PPDU and the presentation-connection shall be
released.

6.4.4.2 Protocol error

      When a PPM receives an unrecognized or unexpected PPDU, or an
unexpected  session-service primitive, it shall issue  a  P-P-ABORT
indication  service primitive and, if possible, send an  ARP  PPDU.
The presentation-connection shall be released.

6.4.4.3 Invalid PPDU

      When  a  PPM  receives  a PPDU, containing  an  invalid  PPDU
parameter  value  or an unrecognized or unexpected PPDU  parameter,
including   a   PPDU   with  an  unexpected  presentation   context
identifier,  or  one  for  which the received  bitstring  does  not
represent  a valid presentation data value (including any  embedded
presentation data value) in the corresponding abstract  syntax,  it
shall  issue a P-P-ABORT indication service primitive and  send  an
ARP  PPDU,  if  possible.  The  presentation-connection  shall   be
released.

6.4.4.4 S-P-ABORT

      When  a  PPM receives an S-P-ABORT indication session-service
primitive, it shall issue a P-P-ABORT indication service  primitive
and the presentation-connection shall be released.

6.4.4.5 ARU PPDU

      When  a  PPM receives an ARU PPDU it shall issue a  P-U-ABORT
indication service primitive and the presentation-connection  shall
be released.

6.4.4.6 ARP PPDU

      When  a  PPM receives an ARP PPDU, it shall issue a P-P-ABORT
indication service primitive and the presentation-connection  shall
be released.

      Note  - When the abnormal release procedure is applied during
an attempt to establish a presentation-connection, the presentation-
connection shall not be established.

6.4.5   Collisions and Interactions

      The abnormal release procedure may be used at any time when a
presentation-connection has been established or during presentation-
connection establishment.

6.5  Context Alteration

6.5.1   Purpose

     The context alteration procedure is used to modify the DCS. It
negotiates the definition of one or more new presentation  contexts
to  be  added  to  the DCS, and also the deletion  of  presentation
contexts  which are members of the DCS. It is used by a  requesting
entity   which  has  received  a  P-ALTER-CONTEXT  request  service
primitive.

     The procedure uses the following PPDUs:

     a) AC PPDU,

     b) ACA PPDU.

6.5.2   AC PPDU associated parameters

6.5.2.1 Presentation context addition list

      This  consists of a list containing one or more  items.  Each
item  represents one item of the Presentation context addition list
parameter  from the P-ALTER-CONTEXT request service  primitive  and
shall  be  represented  by  one item of  the  Presentation  context
addition  list parameter of the P-ALTER-CONTEXT indication  service
primitive.  Each  item  contains three components,  a  presentation
context identifier, an abstract syntax name, and a transfer  syntax
list. The transfer syntax list contains those transfer syntax names
(or  the  names of specifications producing such transfer syntaxes)
the  requesting PPM is capable of supporting for the named abstract
syntax.  All  presentation context identifiers  contained  in  this
parameter   shall  be  different  from  the  presentation   context
identifiers  of all presentation contexts in the DCS or  previously
used in any PPDU on the presentation-connection. If the sending PPM
is the initiator, all presentation context identifiers shall be odd
integers, otherwise all shall be even integers.

6.5.2.2 Presentation context deletion list

     This shall be the Presentation context deletion list parameter
from the P-ALTER-CONTEXT request service primitive and shall appear
as the Presentation context deletion list parameter of the P-ALTER-
CONTEXT indication service primitive.

6.5.2.3 User data

      This parameter shall represent the User data parameter of the
P-ALTER-CONTEXT request service primitive and shall be  represented
by the User data parameter of the P-ALTER-CONTEXT indiction service
primitive.  This parameter shall be from presentation  contexts  as
specified in ñ 6.1.2.

6.5.3   ACA PPDU associated parameters

6.5.3.1 Presentation context addition result list

      This shall represent the Presentation context addition result
list  parameter  of the P-ALTER-CONTEXT response service  primitive
and  shall  be  represented  by the Presentation  context  addition
result  list  parameter  of  the  P-ALTER-CONTEXT  confirm  service
primitive.  It  consists of a list containing the  same  number  of
items as the Presentation context addition list parameter of the AC
PPDU.  Each item shall be a reply to the corresponding item in  the
AC  PPDU and contains one or two components, a presentation context
addition  result  and  an  optional component  which  is  either  a
transfer syntax name (or the name of a specification producing such
a transfer syntax) or a provider reason.

     The presentation context addition result shall take one of the
values:

     -  ╥acceptance╙;

     -  ╥user-rejection╙;

     -  ╥provider-rejection╙.

      The transfer syntax name shall be present if the presentation
context  addition result takes the value ╥acceptance╙. It shall  be
one  of  the  names  proposed  by the requesting  PPM  as  possible
transfer  syntaxes  for  the identified presentation  context,  and
shall  determine  the transfer syntax which the accepting  PPM  has
selected.

      The  provider  reason shall be present  if  the  presentation
context  addition  result takes the value ╥provider-rejection╙.  It
specifies  the  reason  for rejection of the  presentation  context
addition by the accepting PPM and shall take one of the values:

     -  reason not specified;

     -  abstract syntax not supported;

     -  proposed transfer syntaxes not supported;

     -  local limit on DCS exceeded.

6.5.3.2 Presentation context deletion result list

      This  shall be the Presentation context deletion result  list
parameter  of  the P-ALTER-CONTEXT response service  primitive  and
shall  appear  as  the  Presentation context deletion  result  list
parameter  of  the  P-ALTER-CONTEXT confirm service  primitive.  It
consists  of  a  list containing the same number of  items  as  the
Presentation context deletion list parameter of the AC  PPDU.  Each
item shall refer to the corresponding item in the AC PPDU and shall
take one of the values:

     -  ╥acceptance╙;

     -  ╥user-rejection╙.

6.5.3.3 User data

      This parameter shall represent the User data parameter of the
P-ALTER-CONTEXT response service primitive and shall be represented
by  the  user data parameter of the P-ALTER-CONTEXT confirm service
primitive.  This parameter shall be from presentation  contexts  as
specified in ñ 6.1.2.

6.5.4   Procedure

6.5.4.1  When  a  P-ALTER-CONTEXT  request  service  primitive   is
received by a PPM (the requestor), it shall send an AC PPDU.

      Note - Those presentation contexts proposed for deletion  are
still  available  for presentation data values  in  the  User  data
parameter of the AC PPDU.

6.5.4.2 When an AC PPDU is received by a PPM (the acceptor). It may
itself  refuse  some  or all of the proposed  presentation  context
additions.  It  shall  issue a P-ALTER-CONTEXT  indication  service
primitive  in  which it shall mark refused addition proposals  with
the value ╥provider-rejection╙.

6.5.4.3  When  a  P-ALTER-CONTEXT  response  service  primitive  is
received by the accepting PPM, it shall send an ACA PPDU indicating
the  acceptance or rejection of each proposed presentation  context
addition and of each proposed presentation context deletion.

6.5.4.4  When  a  P-ALTER-CONTEXT  response  service  primitive  is
received  by the accepting PPM, the presentation contexts  proposed
for addition and marked with ╥acceptance╙ shall be added to the DCS
and  be available for use from the time of receipt of the response,
and  may also be used for presentation data values contained in the
User  data  parameter  of the ACA PPDU. The  presentation  contexts
proposed for deletion and marked with ╥acceptance╙ shall be deleted
from  the  DCS  and no longer available for use from  the  time  of
receipt  of  the  response, and shall not be used for  presentation
data values contained in the User data parameter of the ACA PPDU.

6.5.4.5  When  an  ACA PPDU is received by the requesting  PPM,  it
shall issue a P-ALTER-CONTEXT confirm service primitive.

6.5.4.6  When  an ACA PPDU is received by the requesting  PPM,  the
presentation contexts accepted in the ACA PPDU shall  be  added  to
the  DCS and be available for use from the time of receipt  of  the
ACA  PPDU,  and  shall  be  accepted for presentation  data  values
contained  in the User data parameter of the ACA PPDU  itself.  The
presentation contexts accepted for deletion in the ACA  PPDU  shall
be deleted from the DCS and no longer be available for use from the
time of receipt of the ACA PPDU.

6.5.5   Collisions and interactions

6.5.5.1 AC PPDU

      Simultaneous  P-ALTER-CONTEXT request service  primitives  by
both   PS-users  shall  be  treated  independently  by  the   PPMs.
Independent treatment of the simultaneous deletion requests applies
even  if  the  two  PS-users have specified the  same  presentation
context for removal from the DCS.

      As a result of the independent treatment of the two requests,
and  the  freedom  of  each PS-user to either accept  or  reject  a
proposal  for presentation context deletion by the peer PS-user,  a
PPM  must be prepared for the following cases, which shall  not  be
treated as errors:

      a)  Receipt  of a P-ALTER-CONTEXT response service  primitive
specifying deletion of a presentation context which is not a member
of  the DCS, but responding to a P-ALTER-CONTEXT indication service
primitive; in this case, the PPM shall send an ACA PPDU  using  the
value of the Presentation context deletion result list parameter of
the P-ALTER-CONTEXT response service primitive;

       b)  Receipt  of  an  ACA  PPDU  specifying  deletion  of   a
presentation  context  which  is not  a  member  of  the  DCS,  but
responding  to an AC PPDU; in this case, the PPM shall issue  a  P-
ALTER-CONTEXT  confirm  service primitive  with  the  corresponding
Presentation context deletion result list parameter value.

6.5.5.2 P-U-ABORT, ARU PPDU, ARP PPDU and S-P-ABORT

     See ñ 6.4.

6.5.5.3 Destructive session services

      If  the sender of an AC PPDU receives an RS PPDU, or an  S-U-
EXCEPTION-REPORT,  S-P-EXCEPTION-REPORT, S-ACTIVITY-DISCARD  or  S-
ACTIVITY-INTERRUPT  indication  service  primitive  before  it  has
received an ACA PPDU, it shall not issue a P-ALTER-CONTEXT  confirm
service primitive, and the PPM shall continue with the procedure as
specified for the disrupting service or RS PPDU.

6.6  Information transfer

6.6.1   Purpose

       The   information  transfer  procedure  is  used  to  convey
presentation data values (including any embedded presentation  data
values)  originating  from P-DATA, P-TYPED-DATA,  P-CAPABILITY-DATA
and  P-EXPEDITED-DATA request service primitives, and P-CAPABILITY-
DATA response service primitives.

     The procedure uses the following PPDUs:

     a) TD PPDU;

     b) TTD PPDU;

     c) TE PPDU;

     d) TC PPDU;

     e) TCC PPDU.

6.6.2   PPDU associated parameters

      Each  of  the  PPDUs  used by this  procedure  has  a  single
parameter.

6.6.2.1 User data

      This  parameter shall represent the User data parameter  from
the  corresponding request or response service primitive and  shall
appear  as  the User data parameter of the corresponding indication
or  confirm service primitive, as appropriate. For the TE PPDU, the
parameter  contains  presentation  data  values  from  the  default
context.  For the TD, TTD, TC and TCC PPDUs, the parameter contains
presentation data values (including any embedded presentation  data
values) from presentation contexts specified in ñ 6.1.2.

6.6.3   Procedure

6.6.3.1  When a P-DATA request service primitive is received  by  a
PPM,  it  shall send a TD PPDU to transmit according to the  agreed
transfer  syntaxes  the  presentation data  values  (including  any
embedded presentation data values) expressed in the P-DATA  request
service primitive. When a PPM receives a TD PPDU, it shall issue  a
P-DATA  indication service primitive containing these  presentation
data values (including any embedded presentation data values).

6.6.3.2  When a P-TYPED-DATA request service primitive is  received
by  a  PPM, it shall send a TTD PPDU to transmit according  to  the
agreed  transfer  syntaxes the presentation data values  (including
any  embedded  presentation data values) expressed in the  P-TYPED-
DATA request service primitive. When a PPM receives a TTD PPDU,  it
shall  issue a P-TYPED-DATA indication service primitive containing
these presentation data values (including any embedded presentation
data values).

     The TTD PPDU shall only be available if the session typed data
functional unit has been proposed and selected in the User  session
requirements parameters of both the CP and CPA PPDUs.

6.6.3.3  When  a  P-EXPEDITED-DATA  request  service  primitive  is
received  by a PPM, it shall send a TE PPDU to transmit,  according
to  the  transfer  syntax of the default context, the  presentation
data  values  (including  any embedded  presentation  data  values)
expressed in the P-EXPEDITED-DATA request service primitive. When a
PPM   receives  a  TE  PPDU,  it  shall  issue  a  P-EXPEDITED-DATA
indication  service  primitive containing these  presentation  data
values (including any embedded presentation data values).

6.6.3.4  When  a  P-CAPABILITY-DATA request  service  primitive  is
received by a PPM, it shall send a TC PPDU to transmit according to
the   agreed   transfer  syntaxes  the  presentation  data   values
(including any embedded presentation data values) expressed in  the
P-CAPABILITY-DATA request service primitive. When a PPM receives  a
TC  PPDU,  it  shall  issue a P-CAPABILITY-DATA indication  service
primitive containing these presentation data values (including  any
embedded  presentation  data values). If  the  accepting  PPM  then
receives  a P-CAPABILITY-DATA response service primitive, it  shall
send  a  TCC  PPDU  to  transmit according to the  agreed  transfer
syntaxes  the  presentation  data values  (including  any  embedded
presentation   data  values)  expressed  in  the  P-CAPABILITY-DATA
response primitive. When a PPM receives a TCC PPDU, it shall  issue
a  P-CAPABILITY-  DATA confirm service primitive  containing  these
presentation data values (including any embedded presentation  data
values).

6.6.4   Collisions and interactions

6.6.4.1 P-U-ABORT, ARU PPDU, ARP PPDU and S-P-ABORT

     See ñ 6.4.

6.7  Token handling

6.7.1   Purpose

      The token handling procedure is used to make available to PS-
users  the token handling facilities of the session-service. It  is
used  by a PPM to support the P-TOKEN-GIVE, P-TOKEN-PLEASE  and  P-
CONTROL- GIVE request and indication service primitives.

6.7.2   Procedure

6.7.2.1  PPDUs are not explicitly defined, but implicitly given  by
the description of mapping in ñ 7.

6.7.2.2 The User data parameters of session-service primitives used
shall  represent or be represented by the User data  parameters  of
the  associated presentation-service primitives and shall  be  from
presentation contexts as specified in ñ 6.1.2.

6.8  Synchronization and resynchronization

6.8.1   Purpose

      The  synchronization and resynchronization procedure are used
to   make   available   to   PS-users   the   synchronization   and
resynchronization facilities of the session-service. They are  used
by   a  PPM  to  support  the  P-SYNC-MINOR,  P-SYNC-MAJOR  and  P-
RESYNCHRONIZE  service primitives. The resynchronization  procedure
has  influence  on the DCS when the context restoration  functional
unit has been selected.

     The procedure uses the following PPDUs:

     a) RS PPDU;

     b) RSA PPDU.

6.8.2   RS PPDU associated parameters

6.8.2.1 Resynchronize type

      This  shall be the Resynchronize type parameter from  the  P-
RESYNCHRONIZE  request service primitive and shall  appear  as  the
Resynchronize  type  parameter  of the  P-RESYNCHRONIZE  indication
service primitive.

6.8.2.2 Synchronization point serial number

       This  shall  be  the  Synchronization  point  serial  number
parameter  from the P-RESYNCHRONIZE request service  primitive  and
shall  appear as the Synchronization point serial number  parameter
of the P-RESYNCHRONIZE indication service primitive.

6.8.2.3 Tokens

      This  shall  be the Tokens parameter from the P-RESYNCHRONIZE
request  service primitive and shall appear as the Tokens parameter
of the P-RESYNCHRONIZE indication service primitive.

6.8.2.4 Presentation context identifier list

      This  consists  of  a  list, each  entry  of  which  has  two
components,  a  presentation context identifier and  an  associated
transfer syntax name. The list shall specify the DCS which  results
from the RS PPDU.

6.8.2.5 User data

      This parameter shall represent the User data parameter of the
P-RESYNCHRONIZE request service primitive and shall be  represented
by  the  User  data  parameter  of the  P-RESYNCHRONIZE  indication
service  primitive.  This  parameter  shall  be  from  presentation
contexts as specified in ñ 6.1.2.

6.8.3   RSA PPDU associated parameters

6.8.3.1 Synchronization point serial number

       This  shall  be  the  Synchronization  point  serial  number
parameter  from  the P-RESYNCHRONIZE response primitive  and  shall
appear as the Synchronization point serial number parameter of  the
P-RESYNCHRONIZE confirm service primitive.

6.8.3.2 Tokens

      This  shall  be the Tokens parameter from the P-RESYNCHRONIZE
response service primitive and shall appear as the Tokens parameter
of the P-RESYNCHRONIZE confirm service primitive.

6.8.3.3 Presentation context identifier list

      This  consists  of  a  list, each  entry  of  which  has  two
components,  a  presentation context identifier and  an  associated
transfer syntax name. The list shall specify the DCS which  results
from the RSA PPDU.

6.8.3.4 User data

      This parameter shall represent the User data parameter of the
P-RESYNCHRONIZE response service primitive and shall be represented
by  the  User data parameter of the P-RESYNCHRONIZE confirm service
primitive.  This parameter shall be from presentation  contexts  as
specified in ñ 6.1.2.

6.8.4   Procedure

6.8.4.1  The  syncpoint  identifier of a  service  primitive  is  a
syncpoint  identifier where the value of the synchronization  point
serial  number is equal to that of the corresponding  parameter  of
that service primitive.

      The  resync identifier of a service primitive is a  syncpoint
identifier  where  the  value of the synchronization  point  serial
number  is  equal  to that of the corresponding parameter  of  that
service primitive minus one.

6.8.4.2  If a PPM receives a P-SYNC-MINOR request service primitive
or  issues  a  P-SYNC-MINOR indication service  primitive  and  the
context  restoration  functional unit has been  selected,  then  it
shall  associate the current DCS with the syncpoint  identifier  of
the request or indication service primitive.

6.8.4.3 If a PPM receives a P-SYNC-MAJOR response service primitive
or  issues a P-SYNC-MAJOR confirm service primitive and the context
restoration  functional  unit  has been  selected,  then  it  shall
associate  the  current DCS with the syncpoint  identifier  of  the
response or confirm service primitive.

      The  PPM  shall eliminate any associations between  syncpoint
identifiers and DCSs which it had previously made.

6.8.4.4  If  a  PPM  receives  a  P-RESYNCHRONIZE  request  service
primitive  and  the  context  management  functional  unit  is  not
selected then it shall send a RS PPDU.

6.8.4.5  If  a  PPM  receives  a  P-RESYNCHRONIZE  request  service
primitive  and the context management functional unit  is  selected
but the context restoration functional unit is not selected then it
shall  send  a  RS  PPDU. The Presentation context identifier  list
parameter shall correspond to the DCS known to the PPM.

6.8.4.6  If a PPM receives a P-RESYNCHRONIZE request primitive  and
the  context restoration functional unit is selected then it  shall
set the DCS as follows:

      a)  If  the resynchronize type is ╥abandon╙, then the DCS  is
unchanged;

     b) if the resynchronize type is ╥restart╙ or ╥set╙, then:

      i)  if  the  resync identifier of the primitive is associated
with  a  DCS, then the DCS is restored to that associated with  the
resync identifier;

      ii)    if the resync identifier of the primitive is less than
each  syncpoint identifier associated with a DCS, then the  DCS  is
restored to that of the presentation-connection establishment;

     iii)  in all other cases, the DCS is unchanged.

      The  PPM  shall  then  send a RS PPDU with  the  Presentation
context identifier list parameter value corresponding to the DCS.

6.8.4.7  If  a  PPM  receives a RS PPDU and the context  management
functional  unit  is  not  selected,  then  it  shall  issue  a  P-
RESYNCHRONIZE indication service primitive.

6.8.4.8  If  a  PPM  receives a RS PPDU and the context  management
functional unit is selected, but the context restoration functional
unit  is  not  selected, then it shall, if an ACA PPDU is  awaited,
replace  the  DCS  by  that specified in the  Presentation  context
identifier list parameter of the RS PPDU. It shall then (regardless
of  whether  an ACA is awaited) issue a P-RESYNCHRONIZE  indication
service primitive.

6.8.4.9  If  a  PPM receives a RS PPDU and the context  restoration
functional unit is selected, then it shall set the DCS as follows:

     a) if the resynchronize type is ╥abandon╙, then:

     i) if an ACA PPDU is awaited, then the DCS is replaced by that
specified in the Presentation context identifier list parameter  of
the RS PPDU;

      ii)    if  an  ACA  PPDU  is not awaited,  then  the  DCS  is
unchanged;

     b) if the resynchronize type is ╥restart╙ or ╥set╙, then:

      i)  if  the  resync  identifier of the service  primitive  is
associated  with a DCS, then the DCS is restored to that associated
with the resync identifier;

      ii)    if  the resync identifier of the service primitive  is
less than each syncpoint identifier associated with a DCS, then the
DCS   is   restored   to   that   of  the   presentation-connection
establishment;

     iii)  in all other cases, the DCS is set as per (a) above.

      The PPM shall then issue a P-RESYNCHRONIZE indication service
primitive.

6.8.4.10   If  a  PPM receives a P-RESYNCHRONIZE  response  service
primitive  and  the  context  management  functional  unit  is  not
selected, it shall send a RSA PPDU.

6.8.4.11   If  a  PPM receives a P-RESYNCHRONIZE  response  service
primitive  and the context management functional unit  is  selected
then  it shall send a RSA PPDU. The Presentation context identifier
list parameter shall correspond to the DCS known to the PPM.

6.8.4.12   If a PPM receives a RSA PPDU and the context  management
functional  unit  is  not  selected,  then  it  shall  issue  a  P-
RESYNCHRONIZE confirm service primitive.

6.8.4.13   If a PPM receives a RSA PPDU and the context  management
functional  unit is selected but the context restoration functional
unit  is  not  selected,  then it shall replace  the  DCS  by  that
specified in the Presentation context identifier list parameter  of
the PPDU. It shall then issue a P-RESYNCHRONIZE confirm primitive.

6.8.4.14   If a PPM receives a RSA PPDU and the context restoration
functional unit is selected, then it shall set the DCS as follows:

      a)  if  the resynchronize type is ╥abandon╙, then the DCS  is
replaced  by that specified in the Presentation context  identifier
list parameter of the PPDU;

     b) if the resynchronize type is ╥restart╙ or ╥set╙, and either
there  is  no  syncpoint identifier associated with a  DCS  or  the
resync identifier is not associated with a DCS and is greater  than
the  lowest syncpoint identifier associated with a DCS, the DCS  is
replaced  by that specified in the Presentation context  identifier
list parameter of the PPDU;

     c) in all other cases, the DCS is unchanged.

      The  PPM  shall then issue a P-RESYNCHRONIZE confirm  service
primitive.

      Note  -  When  receiving a RSA PPDU, the  resynchronize  type
relevant  (for the procedures described above) is the resynchronize
type of the associated RS PPDU.

6.8.5   Collisions and Interactions

6.8.5.1 P-U-ABORT, ARU PPDU, ARP PPDU, and S-P-ABORT

     See ñ 6.4.

6.8.5.2 P-ALTER-CONTEXT, AC-PPDU and ACA PPDU

     See ñ 6.5.

6.9  Exception reporting

6.9.1   Purpose

     The exception reporting procedure is used to make available to
PS-users the exception reporting facilities of the session-service.
It is used by a PPM to support the P-U-EXCEPTION-REPORT request and
indication   service   primitive   and   the   P-P-EXCEPTION-REPORT
indication service primitive.

6.9.2   Procedure

6.9.2.1  PPDUs are not explicitly defined, but implicitly given  by
the description of mapping in ñ 7.

6.9.2.2 The User data parameters of session-service primitives used
shall  represent or be represented by the User data  parameters  of
the  associated presentation-service primitives and shall  be  from
presentation contexts as specified in ñ 6.1.2.

6.10 Activity management

6.10.1  Purpose

     The activity management procedure is used to make available to
PS-users the activity management facilities of the session-service.
It is used by a PPM to support the P-ACTIVITY-START and P-ACTIVITY-
RESUME request and indication service primitives and the P-ACTIVITY-
END,    P-ACTIVITY-INTERRUPT   and   P-ACTIVITY-DISCARD    request,
indication, response and confirm service primitives.

      When the context restoration functional unit is selected, the
activity  management procedure has influence on the DCS as  defined
by ñ 6.10.2.

6.10.2  Procedure

6.10.2.1  PPDUs are not explicitly defined, but implicitly given by
the description of mapping in ñ 7.

6.10.2.2   The  User data parameters of session-service  primitives
used  shall represent or be represented by the User data parameters
of the associated presentation-service primitives and shall be from
presentation contexts as specified in ñ 6.1.2.

6.10.2.3  If a PPM receives a P-ACTIVITY-INTERRUPT response service
primitive   or   issues  a  P-ACTIVITY-INTERRUPT  confirm   service
primitive  when  an  activity  is  in  progress  and  the   context
restoration  functional  unit  has been  selected,  then  it  shall
replace the DCS with the inter-activity DCS.

6.10.2.4   If a PPM receives a P-ACTIVITY-DISCARD response  service
primitive, or issues a P-ACTIVITY-DISCARD confirm service primitive
when  an  activity  is  in  progress, and the  context  restoration
functional  unit has been selected, then it shall replace  the  DCS
with   the   inter-activity  DCS.  It  shall  also  eliminate   any
associations  between syncpoint identifiers and DCSs which  it  had
previously made.

6.10.2.5   If  a  PPM  receives a P-ACTIVITY-END  response  service
primitive,  or  issues a P-ACTIVITY-END confirm service  primitive,
and the context restoration functional unit has been selected, then
it shall replace the DCS with the inter-activity DCS. It shall also
eliminate any associations between syncpoint identifiers  and  DCSs
which it had previously made.

6.10.2.6   If  a  PPM receives a P-ACTIVITY-RESUME request  service
primitive   or   issues  a  P-ACTIVITY-RESUME  indication   service
primitive, where the Old session connection identifier parameter is
absent  in  the  request or indication service primitive,  then  it
shall take the following actions:

      a) it shall eliminate any associations between DCSs and pairs
composed  of  the Old activity identifier parameter  value  of  the
request  or  indication service primitive and  any  synchronization
point  serial  number greater than the value of the Synchronization
point serial number parameter.

      b)  if  the pair composed of the Old activity identifier  and
Synchronization point serial number parameter values and has a  DCS
associated with it, then it shall restore the DCS by that one.

7    Mapping of PPDUS onto the session-service

7.1  Connection establishment

7.1.1   CP PPDU

      The CP PPDU shall be conveyed from the initiating PPM to  the
responding  PPM  in  the S-CONNECT request and indication  session-
service primitives.

7.1.1.1 CP PPDU associated parameters

      Table  1/X.226 defines the mapping of the CP PPDU  associated
parameters onto S-CONNECT parameters.


                           TABLE 1/X.226
Mapping of CP PPDU associated parameters onto S-CONNECT parameters

CP PPDU associated parameter      S-CONNECT parameter      m/nm/
                                                             s

Mode selector                  SS-user data                  m
Protocol version               SS-user data                 nm
Calling-presentation-selector  SS-user data                 nm
Calling-session-address        Calling SSAP address          s
Called-presentation-selector   SS-user data                 nm
Called-session-address         Called SSAP address           s
Presentation context           SS-user data                 nm
definition list
Default context name           SS-user data                 nm
Quality of service             Quality of service            s
Presentation requirements      SS-user data                 nm
User session requirements      SS-user data                 nm
Revised session requirements   Session requirements          s
Initial synchronization point  Initial synchronization       s
serial number                  point serial number
Initial assignment of tokens   Initial assignment of         s
                               tokens
Session connection identifier  Session connection            s
                               identifier
User data                      SS-user data                 nm

 m:  mandatory.

nm:  non-mandatory.

s:    as  defined in the Session Service Definition (Recommendation
X.215).

7.1.2   CPA PPDU

      The CPA PPDU shall be conveyed from the responding PPM to the
initiating  PPM  in  the S-CONNECT response  and  confirm  session-
serivce primitive.

7.1.2.1 CPA PPDU associated parameters

      Table  2/X.226 defines the mapping of the CPA PPDU associated
parameters onto S-CONNECT parameters.


                           TABLE 2/X.226
Mapping of CPA PPDU associated parameters onto S-CONNECT parameters

CPA PPDU associated parameter     S-CONNECT parameter      m/nm/
                                                             s
Mode selector                  SS-user data                  m
Protocol version               SS-user data                 nm
Responding-presentation-       SS-user data                 nm
selector
Responding-session-address     Responding SSAP address       s
Presentation context           SS-user data                 nm
definition result list
Quality of service             Quality of service            s
Presentation requirements      SS-user data                 nm
User session requirements      SS-user data                 nm
Revised session requirements   Session requirements          s
Initial synchronization point  Initial synchronization       s
serial number                  point serial number
Initial assignment of tokens   Initial assignment of         s
                               tokens
Session connection identifier  Session connection            s
                               identifier
User data                      SS-user data                 nm

 m:  mandatory.

nm:  non-mandatory.

s:    as  defined in the Session Service Definition (Recommendation
X.215).

7.1.2.2 S-CONNECT Result parameter

     This parameter shall have the value ╥accept╙.

7.1.3   CPR PPDU

      The CPR PPDU shall be conveyed from the responding PPM to the
initiating  PPM  in  the S-CONNECT response  and  confirm  session-
service primitive.

     However, when the session-service-provider rejects the session-
connection  establishment proposal, there is no explicit  S-CONNECT
response session-service primitive and corresponding CPR PPDU.

7.1.3.1 CPR PPDU associated parameters

      Table  3/X.226 defines the mapping of the CPR PPDU associated
parameters onto S-CONNECT parameters.


                           TABLE 3/X.226
Mapping of CPR PPDU associated parameters onto S-CONNECT parameters

CPR PPDU associated parameter     S-CONNECT parameter      m/nm/
                                                             s

Protocol version               SS-user data                 nm
Responding-presentation-       SS-user data                 nm
selector
Responding-session-address     Responding SSAP address       s
Presentation context           SS-user data                 nm
definition result list
Default context result         SS-user data                 nm
Quality of service             Quality of service            s
Session requirements           Session requirements          s
Session connection identifier  Session connection            s
                               identifier
Provider reason                SS-user data                 nm
User data                      SS-user data                 nm

 m:  mandatory.

nm:  non-mandatory.

s:    as  defined in the Session Service Definition (Recommendation
X.215).

7.1.3.2 S-CONNECT Result parameter

     This parameter may take the values:

     -  ╥reject by SS-provider╙ (a whole class of values);

     -  ╥reject by called SS-user╙ with SS-user data.

      The  former  case arises when rejection is initiated  by  the
session-service-provider; the Provider reason parameter  is  absent
even  though  rejection  is initiated by the  presentation-service-
provider. The latter case arises when rejection is initiated by the
responding PPM or PS-user; the Provider reason parameter is present
only if rejection is initiated by the responding PPM. The User data
parameter  of  the  PPDU  may  only be present  when  rejection  is
initiated by the responding PS-user.

7.2  Normal release of connection

      Normal  release  of the presentation-connection  takes  place
concurrently   with   normal  release  of  the  session-connection.
Presentation-service primitives are mapped onto  the  corresponding
session-service primitives. Table 4/X.226 defines the mapping.


                           TABLE 4/X.226
           Mapping of normal release service primitives

    Presentation primitive             Session primitive


P-RELEASE request                S-RELEASE request


P-RELEASE indication             S-RELEASE indication


P-RELEASE response               S-RELEASE response


P-RELEASE confirm               S-RELEASE confirm


7.3  Abnormal release of connection

7.3.1   ARU PPDU

      The ARU PPDU shall be conveyed from the requesting PPM to the
accepting  PPM  in  the S-U-ABORT request and  indication  session-
service primitives.

7.3.1.1 ARU PPDU associated parameters

      Table  5/X.226 defines the mapping of the ARU PPDU associated
parameters onto S-U-ABORT parameters.


                           TABLE 5/X.226
Mapping of ARU PPDU associated parameters onto S-U-ABORT parameters

ARU PPDU associated parameter     S-U-ABORT parameter      m/nm/
                                                             s

Presentation          context  SS-user data                nm
identifier list

User data                      SS-user data                nm

 m:  mandatory.

nm:  non-mandatory.

s:    as  defined in the Session Service Definition (Recommendation
X.215).

7.3.2   ARP PPDU

      The ARP PPDU shall be conveyed from the requesting PPM to the
accepting  PPM  in  the S-U-ABORT request and  indication  session-
service primitives.

7.3.2.1 ARP PPDU associated parameters

      Table  6/X.226 defines the mapping of the ARP PPDU associated
parameters onto S-U-ABORT parameters.


                           TABLE 6/X.226
Mapping of ARP PPDU associated parameters onto S-U-ABORT parameters

ARP PPDU associated parameter      S-U-ABORT parameter     m/nm/
                                                             s


Provider reason                 SS-user data                 nm


Event identifier                SS-user data                 nm


 m:  mandatory.

nm:  non-mandatory.

s:    as  defined in the Session Service Definition (Recommendation
X.215).

7.4  Context Alteration

7.4.1   AC PPDU

      The AC PPDU shall be conveyed from the requesting PPM to  the
accepting PPM in the S-TYPED- DATA request and indication  session-
service primitives.

7.4.1.1 AC PPDU associated parameters

      Table  7/X.226 defines the mapping of the AC PPDU  associated
parameters onto S-TYPED-DATA parameters.

7.4.2   ACA PPDU

      The ACA PPDU shall be conveyed from the accepting PPM to  the
requesting  PPM in the S-TYPED- DATA response and confirm  session-
service primitives.

7.4.2.1 ACA PPDU associated parameters

      Table  8/X.226 defines the mapping of the ACA PPDU associated
parameters onto S-TYPED-DATA parameters.


                           TABLE 7/X.226
    Mapping of AC PPDU associated parameters onto S-TYPED-DATA
                            parameters

AC PPDU associated parameter      S-TYPED-DATA parameter   m/nm/
                                                             s

Presentation context  addition  SS-user data               nm
list

Presentation context  deletion  SS-user data               nm
list

User data                       SS-user data               nm

 m:  mandatory.

nm:  non-mandatory.

s:    as  defined in the Session Service Definition (Recommendation
X.215).


                           TABLE 8/X.226
    Mapping of ACA PPDU associated parameters onto S-TYPED-DATA
                            parameters

ACA PPDU associated parameter    S-TYPED-DATA parameter    m/nm/
                                                             s


Presentation context addition  SS-user data                 nm
result list


Presentation context deletion  SS-user data                 nm
result list


User data                      SS-user data                 nm


 m:  mandatory.

nm:  non-mandatory.

s:    as  defined in the Session Service Definition (Recommendation
X.215).

7.5  Information Transfer

7.5.1   TTD PPDU

      The TTD PPDU shall be conveyed from the requesting PPM to the
accepting PPM in the S-TYPED- DATA request and indication  session-
service primitives.

7.5.1.1 TTD PPDU associated parameters

      Table  9/X.226 defines the mapping of the TTD PPDU associated
parameters onto S-TYPED-DATA parameters.


                           TABLE 9/X.226
    Mapping of TTD PPDU associated parameters onto S-TYPED-DATA
                            parameters

TTD PPDU associated parameter    S-TYPED-DATA parameter    m/nm/
                                                             s


User data                      SS-user data                nm


 m:  mandatory.

nm:  non-mandatory.

s:    as  defined in the Session Service Definition (Recommendation
X.215).

7.5.2   TD PPDU

      The  User data parameter of a TD PPDU shall form the  SS-user
data   parameter  of  an  S-DATA  request  service  primitive   and
corresponding indication service primitive.

7.5.3   TE PPDU

      The  User data parameter of a TE PPDU shall form the  SS-user
data  parameter  of an S-EXPEDITED- DATA request service  primitive
and corresponding indication service primitive.

7.5.4   TC PPDU

      The User data parameter of the TC PPDU shall form the SS-user
data  parameter of an S-CAPABILITY- DATA request service  primitive
and corresponding indication service primitive.

7.5.5   TCC PDU

     The User data parameter of the TCC PPDU shall form the SS-user
data  parameter of an S-CAPABILITY- DATA response service primitive
and corresponding confirm service primitive.

7.6  Token Handling

     Token handling services are provided by the underlying session-
service.  Presentation-service  primitives  are  mapped  onto   the
corresponding  session-service primitives. Table  10/X.226  defines
the mapping.

7.7  Synchronization

      Synchronization  services  are  provided  by  the  underlying
session-service.  The  presentation-service primitives  are  mapped
onto  the  corresponding session-service primitives. Table 11/X.226
defines the mapping.


                          TABLE 10/X.226
           Mapping of token handling service primitives

    Presentation primitive             Session primitive


P-TOKEN-GIVE request             S-TOKEN-GIVE request


P-TOKEN-GIVE indication          S-TOKEN-GIVE indication


P-TOKEN-PLEASE request           S-TOKEN-PLEASE request


P-TOKEN-PLEASE indication        P-TOKEN-PLEASE indication


P-CONTROL-GIVE request           S-CONTROL-GIVE request


P-CONTROL-GIVE indication       S-CONTROL-GIVE indication



                          TABLE 11/X.226
           Mapping of synchronization service primitives

    Presentation primitive              Session primitive


P-SYNC-MINOR request             S-SYNC-MINOR request


P-SYNC-MINOR indication          S-SYNC-MINOR indication


P-SYNC-MINOR response            S-SYNC-MINOR response


P-SYNC-MINOR confirm             S-SYNC-MINOR confirm


P-SYNC-MAJOR request             S-SYNC-MAJOR request


P-SYNC-MAJOR indication          P-SYNC-MAJOR indication


P-SYNC-MAJOR response            S-SYNC-MAJOR response


P-SYNC-MAJOR confirm             S-SYNC-MAJOR confirm


7.8  Resynchronization

7.8.1   RS PPDU

      The RSA PPDU shall be conveyed from the requesting PPM to the
accepting PM in the S-RESYNCHRONIZE request and indication session-
service primitives.

7.8.1.1 RS PPDU associated parameters

      Table  12/X.226 defines the mapping of the RS PPDU associated
parameters onto S-RESYNCHRONIZE parameters.


                          TABLE 12/X.226
   Mapping of RS PPDU associated parameters onto S-RESYNCHRONIZE
                            parameters

RS PPDU associated parameter   S-RESYNCHRONIZE parameter   m/nm/
                                                             s


Resynchronize type             Resynchronize type            s


Synchronization point serial   Synchronization point         s
number                         serial number


Tokens                         Tokens                        s


Presentation context           SS-user data                 nm
identifier list


User data                      SS-user data                 nm


 m:  mandatory.

nm:  non-mandatory.

s:    as  defined in the Session Service Definition (Recommendation
X.215).

7.8.2   RSA PPDU

      The RSA PPDU shall be conveyed from the accepting PPM to  the
requesting PPM in the S-RESYNCHRONIZE response and confirm session-
service primitives.

7.8.2.1 RSA PPDU associated parameters

      Table 13/X.226 defines the mapping of the RSA PPDU associated
parameters onto S-RESYNCHRONIZE parameters.

7.9  Exception Reporting

      Exception  reporting services are provided by the  underlying
session-service. Presentation-service primitives  are  mapped  onto
the   corresponding  session-service  primitives.  Table   14/X.226
defines the mapping.


                          TABLE 13/X.226
  Mapping of RSA PPDU associated parameters onto S-RESYNCHRONIZE
                            parameters

RSA PPDU associated parameter  S-RESYNCHRONIZE parameter   m/nm/
                                                             s


Synchronization point serial   Synchronization point         s
number                         serial number


Tokens                         Tokens                        s


Presentation context           SS-user data                 nm
identifier list


User data                      SS-user data                 nm


 m:  mandatory.

nm:  non-mandatory.

s:    as  defined in the Session Service Definition (Recommendation
X.215).


                          TABLE 14/X.226
         Mapping of Exception reporting service primitives

    Presentation primitive              Session primitive


P-P-EXCEPTION-REPORT indication  S-P-EXCEPTION-REPORT indication


P-U-EXCEPTION-REPORT request     S-U-EXCEPTION-REPORT request


P-U-EXCEPTION-REPORT indication  S-U-EXCEPTION-REPORT indication


7.10 Activity Management

      Activity  management services are provided by the  underlying
session-service. Presentation-service primitives  are  mapped  onto
the   corresponding  session-service  primitives.  Table   15/X.226
defines the mapping.


                          TABLE 15/X.226
   Mapping of Activity management service primitives primitives

    Presentation primitive              Session primitive

P-ACTIVITY-START request         S-ACTIVITY-START request
P-ACTIVITY-START indication      S-ACTIVITY-START indication
P-ACTIVITY-RESUME request        S-ACTIVITY-RESUME request
P-ACTIVITY-RESUME indication     S-ACTIVITY-RESUME indication
P-ACTIVITY-INTERRUPT request     S-ACTIVITY-INTERRUPT request
P-ACTIVITY-INTERRUPT indication  S-ACTIVITY-INTERRUPT indication
P-ACTIVITY-INTERRUPT response    S-ACTIVITY-INTERRUPT response
P-ACTIVITY-INTERRUPT confirm     S-ACTIVITY-INTERRUPT confirm
P-ACTIVITY-DISCARD request       S-ACTIVITY-DISCARD request
P-ACTIVITY-DISCARD indication    S-ACTIVITY-DISCARD indication
P-ACTIVITY-DISCARD response      S-ACTIVITY-DISCARD response
P-ACTIVITY-DISCARD confirm       S-ACTIVITY-DISCARD confirm
P-ACTIVITY-END request           S-ACTIVITY-END request
P-ACTIVITY-END indication        S-ACTIVITY-END indication
P-ACTIVITY-END response          P-ACTIVITY-END response
P-ACTIVITY-END confirm           S-ACTIVITY-END confirm

8    Structure and encoding of PPDUs

8.1  General

8.1.1    The  struture  of  PPDUs  (whether  explicity  defined  or
implicitly given) shall be defined by:

     a) the mapping onto parameters of session-service primitives;

      b)  the  structure of session-service primitive SS-user  data
parameter values.

8.1.2   The structure of SS-user data parameter values is specified
using:

     a) the notation ASN.1 (Recommendation X.208);

     b) additional comments contained in the ASN.1 description;

      Note  - ASN.1 comments in ñ 8.2 are an integral part of  this
Recommendation, and frequently express requirements.

     c) rules of extensibility as specified in ñ 8.5 when operating
in normal mode.

8.1.3    The encoding of SS-user data parameter values is specified
in ñ 8.3.

8.2  Structure of SS-user data parameter values

X.226-PRESENTATION DEFINITIONS :: =

BEGIN

--

-- In X.410-1984 mode, the value of the SS-user data parameter of

-- the S-CONNECT request and indication session-service primitives

-- shall be a CP-type value.

--

-- In normal mode, the value of the SS-user data parameter of the

--  S-CONNECT  request  and  indication session-service  primitives
shall

-- be a CP-type value, followed as a requestor's option by zero or

-- more CPC-type values.

CP-type :: = SET

{     [0]   IMPLICIT Mode-selector

     [1]   IMPLICIT SET

{ COMPONENTS OF Reliable-Transfer-APDUs.RTORQapdu }OPTIONAL

ASN.1  module  Reliable-Transfer-APDUs is defined in Recommendation
X.228.  -- Shall be used for X.410 mode only. Shall be bitwise

-- compatible with CCITT Recommendation X.410-1984.

-- This shall be the User data parameter of

-- the CP PPDU --,

     [2]   IMPLICIT SEQUENCE

     {  [0] IMPLICIT     Protocol-version DEFAULT {version-1},

     [1] IMPLICIT   Calling-presentation-selector OPTIONAL,

     [2] IMPLICIT   Called-presentation-selector OPTIONAL,

     [4] IMPLICIT   Presentation-context-definition-list OPTIONAL,

     [6] IMPLICIT   Default-context-name OPTIONAL,

     [8] IMPLICIT   Presentation-requirements OPTIONAL,

     [9] IMPLICIT   User-session-requirements OPTIONAL,

     -- shall not be present if equal to the Revised session

     -- requirements parameter --,

     User-data OPTIONAL

     } OPTIONAL

     -- Shall be used for normal mode only.

-- Shall be the parameters of the CP PPDU.

-- As an initiator's option, the presentation data values

-- contained in a CP PPDU may be encoded more than once,

-- using CPC-type values, to allow the transfer of the same

-- presentation data values using a number of different

-- transfer syntaxes.

}

--

CPC-type :: = User-data

-- Shall be used for normal mode only.

-- Shall not be present if the Presentation context definition list

-- parameter is not present in the CP PPDU.

--  Each  instance  of  this data type shall  contain  all  of  the
presentation

-- data values which were contained in the User data parameter of

-- the CP PPDU

--  This  shall be the same set of presentation data  values  which
were

-- contained in the CP-type.

-- The SS-user data parameter value of the S-CONNECT

-- response and confirm session-service primitives shall be

-- a CPA-PPDU value when the Result parameter value

-- is ╥accept╙.

--

CPA-PPDU :: = SET

{     [0]   IMPLICIT Mode-selector

     [1]   IMPLICIT SET

     { COMPONENTS OF Reliable-Transfer-APDUs.RTOACapdu } OPTIONAL

     -- Shall be used for X.410 mode only. Shall be bitwise

-- compatible with CCITT Recommendation X.410-1984.

-- This shall be the User data parameter of

-- the CPA PPDU --,

     [2]   IMPLICIT SEQUENCE

     {  [0] IMPLICIT     Protocol-version DEFAULT {version-1},

     [3] IMPLICIT   Responding-presentation-selector OPTIONAL,

       [5]  IMPLICIT    Presentation-context-definition-result-list
OPTIONAL,

     [8] IMPLICIT   Presentation-requirements OPTIONAL,

     [9] IMPLICIT   User-session-requirementsOPTIONAL,

     -- shall not be present if equal to the Revised session

-- requirements parameter --

     User-data OPTIONAL

     } OPTIONAL

     -- Shall be used for normal mode only

}

--

--

-- The SS-user data parameter value of

-- the S-CONNECT response and confirm

-- session-service primitives shall be

-- a CPR-PPDU value when the Result parameter

-- value is ╥reject by SS-provider╙

-- or ╥reject by called SS-user╙.

--

CPR-PPDU :: = CHOICE

{     SET {  COMPONENTS OF Reliable-Transfer-APDUs.RTORJapdu }

     -- Shall be used for X.410 mode only. Shall be bitwise

-- compatible with CCITT Recommendation X.410-1984.

-- This shall be the User data parameter of

-- the CPR PPDU --,

     SEQUENCE {

     [0] IMPLICIT   Protocol-version DEFAULT {version-1},

     [3] IMPLICIT   Responding-presentation-selector OPTIONAL,

       [5]  IMPLICIT    Presentation-context-definition-result-list
OPTIONAL,

     [7] IMPLICIT   Default-context-result OPTIONAL,

     [10] IMPLICIT  Provider-reason OPTIONAL,

     User-data OPTIONAL ,

     SET}

     -- Shall be used for normal mode only. --

}

--

--

-- The S-user data parameter of the S-U-ABORT

-- request and indication service primitives shall be

-- an Abort-type value.

--

Abort-type :: = CHOICE {  ARU-PPDU -- for a P-U-ABORT--,

Abort-type :: = CHOICE {  ARP-PPDU -- for a P-P-ABORT --

Abort-type :: = CHOICE }

--

ARU-PPDU :: = CHOICE

     { SET {   COMPONENTS OF Reliable-Transfer-APDUs.RTABapdu }

     -- Shall be used for X.410 mode only. Shall be bitwise

-- compatible with CCITT Recommendation X.410-1984.

-- This shall be the User data parameter of

-- the ARU PPDU. --,

     [0]   IMPLICIT SEQUENCE

       {    [0]  IMPLICIT      Presentation-context-identifier-list
OPTIONAL,

     User-data OPTIONAL ,

     }

     -- Shall be used for normal mode only.

}

--

ARP-PPDU :: = SEQUENCE

     { provider-reason

     [0] IMPLICIT   Abort-reason OPTIONAL,

     [1] IMPLICIT   Event-identifier OPTIONAL ,

     }

--

--

-- The SS-user data parameter value of

-- the S-TYPED-DATA request and

-- indication service primitives shall be

-- a Typed-data-type value

--

Typed-data-type :: = CHOICE

{     acPPDU

     [0] IMPLICIT AC-PPDU

     -- P-ALTER-CONTEXT

-- request and indication --

     acaPPDU

     [1] IMPLICIT ACA-PPDU

     -- P-ALTER-CONTEXT

-- response and confirm --

     ttdPPDU

     User-data

     -- P-TYPED-DATA

-- request and indication --

}

--

AC-PPDU :: = SEQUENCE

       {    [0]   IMPLICIT       Presentation-context-addition-list
OPTIONAL,

     [1] IMPLICIT   Presentation-context-deletion-list OPTIONAL,

     User-data OPTIONAL ,

     }

--

ACA-PPDU :: = SEQUENCE

      {  [0] IMPLICIT     Presentation-context-addition-result-list
OPTIONAL,

       [1]   IMPLICIT     Presentation-context-deletion-result-list
OPTIONAL,

     User-data OPTIONAL ,

     }

--

-- The SS-user data parameter value of

-- the S-RESYNCHRONIZE request and

-- indication service primitives shall be

-- an RS-PPDU value.

--

RS-PPDU :: = SEQUENCE

       {    [0]  IMPLICIT      Presentation-context-identifier-list
OPTIONAL,

     User-data OPTIONAL ,

     }

--

-- The SS-user data parameter value of

-- the S-RESYNCHRONIZE response and

-- confirm service primitives shall be

-- an RSA-PPDU value.

--

RSA-PPDU :: = SEQUENCE

       {    [0]  IMPLICIT      Presentation-context-identifier-list
OPTIONAL,

     User-data OPTIONAL ,

     }

--

--

-- The SS-user data parameter values of

-- the S-DATA, S-CAPABILITY-DATA,

-- S-EXPEDITED-DATA request and

-- indication session-service primitives and

-- S-CAPABILITY-DATA

-- response and confirm session-service

-- primitives shall be of type User-data.

--

-- The SS-user data parameter values of

-- all other session-service

-- primitives not described above shall

-- be of type User-data.

--

--

--

Abort-reason :: = INTEGER {

     reason-not-specified (0),  }

unrecognized-ppdu (1),  }

unexpected-ppdu (2),  }

unexpected-session-service-primitive (3),  }

unrecognized-ppdu-parameter (4),  }

unexpected-ppdu-parameter (5),  }

invalid-ppdu-parameter-value (6)  }

Abstract-syntax-name :: = OBJECT IDENTIFIER

Called-presentation-selector :: = Presentation Selector

Calling-presentation-selector :: = Presentation Selector

Context-list :: = SEQUENCE OF SEQUENCE {

     Presentation-context-identifier,

Abstract-syntax-name,

SEQUENCE OF Transfer-syntax-name }

Default-context-name :: = SEQUENCE

     [0] IMPLICIT   Abstract-syntax-name,

[1] IMPLICIT   Transfer-syntax-name }

Default-context-result :: = Result

Event-identifier :: = INTEGER {

     cp-PPDU ( 0),  }

cpa-PPDU ( 1),  }

cpr-PPDU ( 2),  }

aru-PPDU ( 3),  }

arp-PPDU ( 4),  }

ac-PPDU ( 5),  }

aca-PPDU ( 6),  }

td-PPDU ( 7),  }

ttd-PPDU ( 8),  }

te-PPDU ( 9),  }

tc-PPDU (10),  }

tcc-PPDU (11),  }

rs-PPDU (12),  }

rsa-PPDU (13),  }

s-release-indication (14),  }

s-release-confirm (15),  }

s-token-give-indication (16),  }

s-token-please-indication (17),  }

s-control-give-indication (18),  }

s-sync-minor-indication (19),  }

s-sync-minor-confirm (20),  }

s-sync-major-indication (21),  }

s-sync-major-confirm (22),  }

s-p-exception-report-indication(23),  }

s-u-exception-report-indication (24),  }

s-activity-start-indication (25),  }

s-activity-resume-indication (26),  }

s-activity-interrupt-indication (27),  }

s-activity-interrupt-confirm (28),  }

s-activity-discard-indication (29),  }

s-activity-discard-confirm (30),  }

s-activity-end-indication (31),  }

s-activity-end-confirm (32)  }

Mode-Selector :: = SET {

     [0] IMPLICIT INTEGER {x410-1984-mode (0), normal-mode (1) } }

Presentation-context-addition-list :: = Context-list

Presentation-context-addition-result-list :: = Result-list

Presentation-context-definition-list :: = Context-list

Presentation-context-definition-result-list :: = Result-list

Presentation-context-deletion-list :: = SEQUENCE OF

     Presentation-context-identifier

Presentation-context-deletion-result-list :: = SEQUENCE OF  INTEGER
{

     Acceptance (0), user-rejection (1) }

Presentation-context-identifier :: = INTEGER

Presentation-context-identifier-list :: = SEQUENCE OF SEQUENCE {

     Presentation-context-identifier,

Transfer-syntax-name }

Presentation-requirements :: = BIT STRING {

     Context-management (0), restoration (1) }

Presentation-selector :: = OCTET STRING

Protocol-version :: = BIT STRING {version-1 (0) }

Provider-reason :: = INTEGER {

     reason-not-specified (0),  }

temporary-congestion (1),  }

local-limit-exceeded (2),  }

called-presentation-address-unknown (3),  }

protocol-version-not-surprised (4),  }

default-context-not-supported (5),  }

user-data-not-readable (6),  }

no-PSAP-available (7)  }

Responding-presentation-selector :: = Presentation-selector

Result :: = INTEGER {

     acceptance (0),  }

user-rejection (1),  }

provider-rejection (2)  }

Result-list :: = SEQUENCE OF SEQUENCE {

     [0] IMPLICIT   Result,

[1] IMPLICIT   Transfer-syntax-nameOPTIONAL,

[2] IMPLICIT INTEGER

provider-reason

     { reason-not-specified (0),

abstract-syntax-not-supported (1),

proposed-transfer-syntaxes-not-supported (2),

local-limit-on-DCS-exceeded (3)  OPTIONAL,

     }

}

Transfer-syntax-name :: = OBJECT IDENTIFIER

User-data :: = CHOICE {

     [APPLICATION 0] IMPLICIT  Simply-encoded-data

[APPLICATION 1] IMPLICIT  Fully-encoded-data }

      --  ñ 8.4 defines when each of the two alternatives shall  be
used.

Simply-encoded-data :: = OCTET STRING

     -- See ñ 8.4.1.

Fully-encoded-data :: = SEQUENCE OF PVD-list

     -- Contains one or more PDV-list values.

-- See ñ 8.4.2.

PDV-list :: = SEQUENCE {

     Transfer-syntax-name OPTIONAL,

Presentation-context-identifier,

presentation-data-values :: = CHOICE {

     single-ASN.1-type [0] ANY,

octet-aligned  [1] IMPLICIT OCTET STRING,

arbitrary  [2] IMPLICIT BIT STRING

}

-- Contains one or more presentation data values from the same

-- presentation context.

-- See ñ 8.4.2.

}

User-session-requirements :: = BIT STRING {

     half-duplex ( 0),  }

duplex ( 1),  }

expedited-data ( 2),  }

minor-synchronize ( 3),  }

major-synchronize ( 4),  }

resynchronize ( 5),  }

activity-management ( 6),  }

negotiated-release ( 7),  }

capability-data ( 8),  }

exceptions ( 9),  }

typed-data (10)  }

END



8.3  Encoding of SS-user data parameter values

8.3.1   Except for type User-data, ASN.1 datatypes specified  in  ñ
8.2  shall  be  encoded according to the Basic Encoding  Rules  for
ASN.1 (Recommendation X.209).

8.3.2   The encoding of values of type User-data is specified in  ñ
8.4.

8.3.3   The encoding of the SS-user data parameter of the S-CONNECT
request   and   indication   service  primitives   shall   be   the
concatenation of the encodings of the CP-type value  and  the  CPC-
type values, if any.

8.4  Encoding of values of type User-data

8.4.1   Simple encoding

8.4.1.1 This encoding shall be used when the User-data value is  of
type Simply-encoded-data.

8.4.1.2  The  User-data value shall be of type  Simply-encoded-data
when the default context is used.

8.4.1.3  The  User-data value shall be of type  Simply-encoded-data
when  the  DCS contains only one member and the context  management
functional unit is not selected.

     Note - This implies that simple encoding cannot be used in the
User data parameter of the CP PPDU, except as in ñ 8.4.1.2.

8.4.1.4 Simple encoding shall be as follows:

If  the  transfer syntax is not self-delimiting, then  there  is  a
danger   that  concatenated  presentation  data  values   will   be
ambiguous. a)  The contents of the Simply-encoded-data value  shall
be  the concatenation of the bitstrings resulting from the encoding
of  the  presentation data values forming the  PS-user  data  value
according to the appropriate transfer syntax.

      b)  Whenever  User-data appears as an element of  some  other
ASN.1  type in ñ 8.2, the encoding of the User-data value shall  be
according  to  the  Basic Encoding Rules for ASN.1  (Recommendation
X.209).

      c) If (b) does not apply, the encoding of the User-data value
shall be the contents octets of the Simply-encoded-data value (i.e.
no  identfier  octets  and no length octets) as  specified  in  (a)
above.

      Note  - When using simple encoding, the transfer syntax  used
shall  either  produce octet-aligned encodings  or  self-delimiting
bitstrings (this is not the general case with transfer syntaxes).

8.4.2   Full encoding

8.4.2.1 This encoding shall be used when the User-data value is  of
type Fully-encoded-data.

8.4.2.2  The  User-data  value shall be of type  Fully-encoded-data
when the default context is not in use and:

     a) the DCS contains more than one member; or

     b) the context management functional unit has been selected.

8.4.2.3 The User-data value shall be of type Fully-encoded-data  in
the  CP-type  and CPC-type, except when the default context  is  in
use.

8.4.2.4  Full  encoding  shall  be the  application  of  the  Basic
Encoding  Rules  for  ASN.1 (Recommendation X.209)  to  the  Fully-
encoded-data value. The structure and contents of the presentation-
data-values component of a PDV-list value shall be as specified  in
ñ 8.4.2.5.

8.4.2.5 The presentation-data-values component of a PDV-list  value
shall  be  encoded according to the Basic Encoding Rules for  ASN.1
(Recommendation  X.209). The various options for the  presentation-
data-values  component  of the PDV-list  value  shall  be  used  as
follows:

      a)  If  the  PDV-list value contains exactly one presentation
data  value which is a single ASN.1 type encoded according  to  the
Basic  Encoding  Rules for ASN.1 (Recommendation X.209),  then  the
option ╥single-ASN1-type╙ shall be used.

      b) If the encodings of the presentation data values contained
in the PDV-list value are each an integral number of octets and (a)
does  not apply, then the option ╥octet-aligned╙ shall be used.  In
this  case,  the contents octets of the OCTET STRING shall  be  the
concatenation of the bitstrings resulting from the encoding of  the
presentation data values contained in that PDV-list value according
to the appropriate transfer syntax.

      c)  If  neither  (a) nor (b) applies, the option  ╥arbitrary╙
shall  be used. The contents octets of the BIT STRING shall be  the
concatenation of the bitstrings resulting from the encoding of  the
presentation data values contained in that PDV-list value according
to the appropriate transfer syntax.

8.4.2.6 The presentation-context-identifier component of a PDV-list
value  in a CP PPDU shall identify the presentation context of  the
presentation data values.

8.4.2.7 The transfer-syntax-name component of a PDV-list value in a
CP  PPDU  shall be present when more than one transfer syntax  name
was proposed for the presentation context of the presentation-data-
values.

8.4.3   Encoding of presentation data values in X.410-1984 mode

8.4.3.1  Except  for  the  S-DATA request  and  indication  service
primitives,  presentation data values in type  User-data  shall  be
encoded according to Basic Encoding Rules for ASN.1 (Recommendation
X.209).

8.4.3.2  For  the S-DATA request and indication service primitives,
presentation data values in type User-data shall be encoded as  the
contents octets (i.e. no identifier octets and no length octets) of
the  primitive encoding of a value of type OCTET STRING,  according
to the Basic Encoding Rules for ASN.1 (Recommendation X.209).

8.5  Rules of extensibility for normal mode

8.5.1   For the CP-PPDU, a receiving PPM shall:

     a) ignore any undefined element;

      b)  where  named  bits are used in ñ 8.2, treat  any  bit  as
insignificant when no name is assigned to it.

8.5.2    Except  as  specified in ñ 8.5.1, where named  numbers  or
named bits are used in ñ 8.2, presence of a number or bit shall  be
invalid when no name is assigned to it.

9    Conformance

9.1  Dynamic Conformance

      A  system  claiming conformance to this Recommendation  shall
exhibit external behaviour consistent with having implemented:

      a)  a  PPM  as  defined by Section 6  and  Annex  A  of  this
Recommendation;

      b) use of the session-service as defined by Section 7 of this
Recommendation;

      c)  encoding  of  PPDUs  as defined  by  Section  8  of  this
Recommendation.

9.2  Static Conformance

      A system claiming conformance to this Recommendation shall be
capable of:

      a) supporting normal mode, X.410-1984 mode, or both. A system
claiming   to   implement   the  procedures   specified   in   this
Recommendation   supports  the  procedures   specified   in   CCITT
Recommendation  X.410-1984 when operating  in  X.410-1984  mode.  A
system  claiming  to  implement the procedures  specified  in  this
Recommendation other than in support of the procedures specified in
CCITT Recommendation X.410-1984 shall operate in normal mode.

     b) initiating a presentation-connection (by sending a CP PPDU)
or responding to a CP PPDU or both;

      c) following all the remaining procedures in the presentation
kernel functional unit;

      d)  following all the Presentation Layer procedures for  each
presentation  functional unit that the system claims  to  implement
and  for  each session functional unit which the system  claims  to
support;

      e) supporting the mapping onto the session-service defined in
Section 7 of this Recommendation;

      f)  in normal mode, following the procedures of the rules  of
extensibility (ñ 8.5).

9.3  Protocol implementation conformance statement

     The Protocol Implementation Conformance Statement accompanying
a  system  for which conformance to this Recommendation is  claimed
shall include statements of the following:

     a) which session functional units are supported;

     b) which presentation functional units are implemented;

      c)  whether it supports initiating a presentation-connection,
responding to a CP-PPDU or both;

     d) which transfer syntaxes it supports;

      e)  whether there is any resource-dependent limit  which  can
cause provider rejection of a service primitive and if so, how this
limit is specified;

     f) whether it supports normal mode, X.410-1984 mode or both.

                              ANNEX A

                     (to Recommendation X.226)

                           State tables

A.1. General

      This  annex describes the presentation protocol in  terms  of
state  tables.  The state tables show the state of a  presentation-
connection, the events that occur in the protocol, the action taken
and the resultant state.

      These  State Tables do not constitute a formal definition  of
the  presentation  protocol; they are included to  provide  a  more
precise  specification  of the elements of procedure  described  in
Section 6.

      Table A-1/X.226 specifies the abbreviated name, category  and
name of each incoming event. The categories are PS-user event,  SS-
provider event and valid PPDU event.

      Table  A-2/X.226 specifies the abbreviated name and  name  of
each state.

      Table A-3/X.226 specifies the abbreviated name, category  and
name  of each outgoing event. The categories are PS-provider event,
SS-user event and PPDU event.

     Table A-4/X.226 specifies the specific actions.

     Table A-5/X.226 specifies the predicates.

     Tables A-6/X.226 to A-14/X.226 specify the state tables.

A.2  Notation for State Tables

A.2.1   Incoming events, states and outgoing events are represented
by their abbreviated names.

A.2.2   Specific actions are represented by the notation [n], where
n is the number of the specific action in Table A-4/X.226.

A.2.3   Predicates are represented by the notation pnn, where nn is
the number of the predicate in Table A-5/X.226.

A.2.4     Boolean  operators  are  represented  by  the   following
notation:

     &  AND

     Ö  NOT

     OR OR

A.3  Conventions for entries in State Tables

A.3.1   The intersection of each state and incoming event which  is
invalid is left blank.

A.3.2   The intersection of each state and incoming event which  is
valid contains entries which are either

     a) an action list which

     i) may contain outgoing events and/or specific actions;

     ii)   always contains the resultant state;

or

     b) one or more conditional action lists, each consist of

      i)  a  predicate expression comprising predicates and boolean
operators;

     ii)   an action list (as in ñ A.3.2 a)).

      Note - The action lists and conditional action lists use  the
notation in ñ A.2.

A.4  Actions to be taken by the PPM

     The state tables define the actions to be taken by the PPM.

A.4.1   Invalid intersections

      If  the  intersection of the state and an incoming  event  is
invalid, one of the following actions shall be taken.

A.4.1.1   If the incoming event comes from the PS-user, any  action
taken by the PPM is a local matter.

      Note  -  One  reason  for  the request  or  response  service
primitive  being  invalid  is  that  the  resulting  SS-user   data
parameter exceeds a length limit imposed by the underlying session-
service. This occurrence and its resolution are local matters.

A.4.1.2  If the incoming event is related to a received PPDU or SS-
provider  event, the PPM shall issue an ARP PPDU (if  there  is  an
underlying session-connection) and a P-P-ABORT indication.

A.4.2   Valid intersections

      If the intersection of the state and incoming event is valid,
one of the following actions shall be taken.

A.4.2.1  If the intersection contains an action list, the PPM shall
take  the  specific  actions in the order specified  in  the  state
table.

A.4.2.2   If  the  intersection contains one  or  more  conditional
action  lists, for each predicate expression that is true  the  PPM
shall  take  the specific actions in the order given in the  action
list  associated  with the predicate expression.  If  none  of  the
predicate  expressions  are true, the PPM shall  take  one  of  the
actions  defined  in  ñ  A.4.1. The  order  of  evaluation  of  the
predicate  expressions  in different conditional  action  lists  is
determined by the order of the conditional action lists.

A.4.3   Receipt of PPDUs

A.4.3.1  Valid PPDUs

      The  PPM shall process valid PPDUs as specified in Tables  A-
6/X.226 to A-14/X.226. See also ñ 8.5.

A.4.3.2  Invalid PPDUs

     If an invalid PPDU is received, the PPM shall take the actions
defined in ñ A.4.1.2.

A.5  Definition of sets and variables

     The following sets and variables are specified.

A.5.1   Functional units

      A set of functional units used in the procedures specified in
this annex is defined as

     fu-dom = (CM, CR)

where

     CM = Context management functional unit

     CR = Context restoration functional unit

     A boolean function FU is defined over fu-dom as follows

     for f in fu-dom

      FU(f) = true   if and only if the functional unit f has  been
selected during the presentation-connection establishment phase.

A.5.2   Context sets

      In  addition  to  the  defined context set  (DCS),  which  is
implicitly   used   for   information  transfer   operations,   the
presentation-entity  needs to be aware  of  the  following  context
sets:

      a)  presentation  contexts proposed for  addition,  initiated
locally;

      b)  presentation  contexts proposed for  addition,  initiated
remotely;

      c)  presentation  contexts proposed for  deletion,  initiated
locally;

      d)  presentation  contexts proposed for  deletion,  initiated
remotely;

        e)    the   DCS   agreed   during   presentation-connection
establishment;

     f) the inter-activity DCS;

     g) the contents of the DCS at synchronization points.

A.5.3   Variables

A.5.3.1  aep

     aep is a boolean variable having the following values:

     aep = true:    Activity end pending.

     aep = false:   Activity end not pending.

     aep is set as follows:

      a)  aep  is set true when an S-ACTIVITY-END response  service
primitive has been issued but while it is still possible to receive
an S-ACTIVITY-INTERRUPT indication service primitive;

      b)  aep  is  set  false  during  the  presentation-connection
establishment   phase,  or  on  receipt  of   any   session-service
indication  primitive  after  an  S-ACTIVITY-END  response  service
primitive has been issued.

A.5.3.2  rl

     rl is a boolean variable having the following values:

     rl = true:     Release phase started.

      rl  = false:    Release phase not started or release has been
rejected.

     rl is set as follows:

       a)  rl  is  set  false  during  the  presentation-connection
establishment  phase  or  when  a  P-RELEASE  response  or  confirm
negative service primitive is issued;

      b)  rl  is  set  true when a P-RELEASE request or  indication
service primitive has been issued.

A.5.3.3  cr

     cr is a boolean variable having the following values:

     cr = true:     A collision of release requests is detected.

      cr  =  false:     There has not been a collision  of  release
requests or the collision has been resolved.

     cr is set as follows:

       a)  cr  is  set  false  during  the  presentation-connection
establishment phase, or when rl is true and a P-RELEASE response or
confirm service primitive is issued;

      b)  cr  is set true if rl is true and a P-RELEASE request  or
indication service primitive is issued.

A.6  Relationship to session-service

       In   general,   the  behaviour  of  the  PPM  is   specified
independently  of  the  behaviour  of  the  session-service.   That
invocations  of presentation-service primitives are  acceptable  to
the   PPM   does  not  imply  that  the  resulting  session-service
primitives will be acceptable to the session-service-provider.

     Events shown in the Tables as generated by the session-service-
provider  or issued to the session-service-provider are  implicitly
conditional on the appropriate session functional unit being agreed
at session-connection establishment.
                          TABLE A-1/X.226
                        Incoming Event List

Abbreviated  Category        Name and Description
    Name

AC           PPDU       ALTER CONTEXT
ACA          PPDU       ALTER CONTEXT ACKNOWLEDGE
ARP          PPDU       PROVIDER ABORT
ARU          PPDU       USER ABORT
CP           PPDU       PRESENTATION CONNECT
CPA          PPDU       PRESENTATION CONNECT ACCEPT
CPR          PPDU       PRESENTATION CONNECT REJECT
P-ACTDreq    PS         P-ACTIVITY-DISCARD request
             primitiv
             e
P-ACTDrsp    PS         P-ACTIVITY-DISCARD response
             primitiv
             e
P-ACTEreq    PS         P-ACTIVITY-END request
             primitiv
             e
P-ACTErsp    PS         P-ACTIVITY-END response
             primitiv
             e
P-ACTIreq    PS         P-ACTIVITY-INTERRUPT request
             primitiv
             e
P-ACTIrsp    PS         P-ACTIVITY-INTERRUPT response
             primitiv
             e
P-ACTRreq    PS         P-ACTIVITY-RESUME request
             primitiv
             e
P-ACTSreq    PS         P-ACTIVITY-START request
             primitiv
             e
P-ALTERreq   PS         P-ALTER-CONTEXT request
             primitiv
             e
P-ALTERrsp   PS         P-ALTER-CONTEXT response
             primitiv
             e
P-CDreq      PS         P-CAPABILITY-DATA request
             primitiv
             e
P-CDrsp      PS         P-CAPABILITY-DATA response
             primitiv
             e
P-CGreq      PS         P-CONTROL-GIVE request
             primitiv
             e
P-CONreq     PS         P-CONNECT request
             primitiv
             e
P-CONrsp+    PS         P-CONNECT response accept
             primitiv
             e
P-CONrsp-    PS         P-CONNECT response reject
             primitiv
             e
P-DTreq      PS         P-DATA request
             primitiv
             e
P-EXreq      PS         P-EXPEDITED-DATA request
             primitiv
             e
P-GTreq      PS         P-TOKEN-GIVE request
             primitiv
             e
P-PTreq      PS         P-TOKEN-PLEASE request
             primitiv
             e
P-RELreq     PS         P-RELEASE request
             primitiv
             e
P-RELrsp+    PS         P-RELEASE response accept
             primitiv
             e
P-RELrsp-    PS         P-RELEASE response reject
             primitiv
             e
P-RSYNreq    PS         P-RESYNCHRONIZE request
             primitiv
             e
P-RSYNrsp    PS         P-RESYNCHRONIZE response
             primitiv
             e
P-SYNMreq    PS         P-SYNC-MAJOR request
             primitiv
             e
P-SYNMrsp    PS         P-SYNC-MAJOR response
             primitiv
             e
P-SYNmreq    PS         P-SYNC-MINOR request
             primitiv
             e
P-SYNmrsp    PS         P-SYNC-MINOR response
             primitiv
             e
P-TDreq      PS         P-TYPED-DATA request
             primitiv
             e
P-UABreq     PS         P-U-ABORT request
             primitiv
             e
P-UERreq     PS         P-U-EXCEPTION-REPORT request
             primitiv
             e


                    TABLE A-1/X.226 (continued)
                        Incoming Event List

Abbreviated  Category        Name and Description
    Name

RS           PPDU       RESYNCHRONIZE
RSA          PPDU       RESYNCHRONIZE ACKNOWLEDGE
S-ACTDcnf    SS         S-ACTIVITY-DISCARD confirm
             primitiv
             e
S-ACTDind    SS         S-ACTIVITY-DISCARD indication
             primitiv
             e
S-ACTEcnf    SS         S-ACTIVITY-END confirm
             primitiv
             e
S-ACTEind    SS         S-ACTIVITY-END indication
             primitiv
             e
S-ACTIcnf    SS         S-ACTIVITY-INTERRUPT confirm
             primitiv
             e
S-ACTIind    SS         S-ACTIVITY-INTERRUPT
             primitiv   indication
             e
S-ACTRind    SS         S-ACTIVITY-RESUME indication
             primitiv
             e
S-ACTSind    SS         S-ACTIVITY-START indication
             primitiv
             e
S-CGind      SS         S-CONTROL-GIVE indication
             primitiv
             e
S-CONcnf-    SS         S-CONNECT confirm reject
             primitiv   (provider)
             e
S-GTind      SS         S-TOKEN-GIVE indication
             primitiv
             e
S-P-ABind    SS         S-P-ABORT indication
             primitiv
             e
S-PERind     SS         S-P-EXCEPTION-REPORT
             primitiv   indication
             e
S-PTind      SS         S-TOKEN-PLEASE indication
             primitiv
             e
S-RELcnf+    SS         S-RELEASE confirm accept
             primitiv
             e
S-RELcnf-    SS         S-RELEASE confirm reject
             primitiv
             e
S-RELind     SS         S-RELEASE indication
             primitiv
             e
S-RSYNcnf    SS         S-RESYNCHRONIZE confirm
             primitiv
             e
S-RSYNind    SS         S-RESYNCHRONIZE indication
             primitiv
             e
S-SYNMcnf    SS         S-SYNC-MAJOR confirm
             primitiv
             e
S-SYNMind    SS         S-SYNC-MAJOR indication
             primitiv
             e
S-SYNmcnf    SS         S-SYNC-MINOR confirm
             primitiv
             e
S-SYNmind    SS         S-SYNC-MINOR indication
             primitiv
             e
S-UERind     SS         S-U-EXCEPTION-REPORT
             primitiv   indication
             e
TC           PPDU       CAPABILITY DATA
TCC          PPDU       CAPABILITY DATA ACKNOWLEDGE
TD           PPDU       DATA
TE           PPDU       EXPEDITED DATA
TTD          PPDU       TYPED DATA


                          TABLE A-2/X.226
                              States

Abbrevi            Name and Description
 ated
 Name


STAI0   idle - no connection


STAI1   await CPA PPDU


STAI2   await P-CONNECT response


STAt0   connected - data transfer


STAac0  await ACA PPDU


STAac1  await P-ALTER-CONTEXT response


STAac2  await ACA PPDU or P-ALTER-CONTEXT
        response



                          TABLE A-3/X.226
                        Outgoing Event List

Abbreviate  Category             Name and Description
  d Name

AC          PPDU      ALTER CONTEXT
ACA         PPDU      ALTER CONTEXT ACKNOWLEDGE
ARP         PPDU      PROVIDER ABORT
ARU         PPDU      USER ABORT
CP          PPDU      PRESENTATION CONNECT
CPA         PPDU      PRESENTATION CONNECT ACCEPT
CPR         PPDU      PRESENTATION CONNECT REJECT
P-ACTDcnf   PS        P-ACTIVITY-DISCARD confirm
            primitiv
            e
P-ACTDind   PS        P-ACTIVITY-DISCARD indication
            primitiv
            e
P-ACTEcnf   PS        P-ACTIVITY-END confirm
            primitiv
            e
P-ACTEind   PS        P-ACTIVITY-END indication
            primitiv
            e
P-ACTIcnf   PS        P-ACTIVITY-INTERRUPT confirm
            primitiv
            e
P-ACTIind   PS        P-ACTIVITY-INTERRUPT indication
            primitiv
            e
P-ACTRind   PS        P-ACTIVITY-RESUME indication
            primitiv
            e
P-ACTSind   PS        P-ACTIVITY-START indication
            primitiv
            e
P-ALTERcnf  PS        P-ALTER-CONTEXT confirm
            primitiv
            e
P-ALTERind  PS        P-ALTER-CONTEXT indication
            primitiv
            e
P-CDcnf     PS        P-CAPABILITY-DATA confirm
            primitiv
            e
P-CDind     PS        P-CAPABILITY-DATA indication
            primitiv
            e
P-CGind     PS        P-CONTROL-GIVE indication
            primitiv
            e
P-CONcnf+   PS        P-CONNECT confirm accept
            primitiv
            e
P-CONcnf-   PS        P-CONNECT confirm reject
            primitiv
            e
P-CONind    PS        P-CONNECT indication
            primitiv
            e
P-DTind     PS        P-DATA indication
            primitiv
            e
P-EXind     PS        P-EXPEDITED-DATA indication
            primitiv
            e
P-GTind     PS        P-TOKEN-GIVE indication
            primitiv
            e
P-PABind    PS        P-P-ABORT indication
            primitiv
            e
P-PERind    PS        P-P-EXCEPTION-REPORT indication
            primitiv
            e
P-PTind     PS        P-TOKEN-PLEASE indication
            primitiv
            e
P-RELcnf+   PS        P-RELEASE confirm accept
            primitiv
            e
P-RELcnf~   PS        P-RELEASE confirm reject
            primitiv
            e
P-RELind    PS        P-RELEASE indication
            primitiv
            e
P-RSYNcnf   PS        P-RESYNCHRONIZE confirm
            primitiv
            e
P-RSYNind   PS        P-RESYNCHRONIZE indication
            primitiv
            e
P-SYNMcnf   PS        P-SYNC-MAJOR confirm
            primitiv
            e
P-SYNMind   PS        P-SYNC-MAJOR indication
            primitiv
            e
P-SYNmcnf   PS        P-SYNC-MINOR confirm
            primitiv
            e
P-SYNmind   PS        P-SYNC-MINOR indication
            primitiv
            e
P-TDind     PS        P-TYPED-DATA indication
            primitiv
            e
P-UABind    PS        P-U-ABORT indication
            primitiv
            e
P-UERind    PS        P-U-EXCEPTION-REPORT indication
            primitiv
            e


                    TABLE A-3/X.226 (continued)
                        Outgoing Event List

Abbreviate  Category             Name and Description
  d Name

RS          PPDU      RESYNCHRONIZE
RSA         PPDU      RESYNCHRONIZE acknowledge
S-ACTDreq   SS        S-ACTIVITY-DISCARD request
            primitiv
            e
S-ACTDrsp   SS        S-ACTIVITY-DISCARD response
            primitiv
            e
S-ACTEreq   SS        S-ACTIVITY-END request
            primitiv
            e
S-ACTErsp   SS        S-ACTIVITY-END response
            primitiv
            e
S-ACTIreq   SS        S-ACTIVITY-INTERRUPT request
            primitiv
            e
S-ACTIrsp   SS        S-ACTIVITY-INTERRUPT response
            primitiv
            e
S-ACTRreq   SS        S-ACTIVITY-RESUME request
            primitiv
            e
S-ACTSreq   SS        S-ACTIVITY-START request
            primitiv
            e
S-CGreq     SS        S-CONTROL-GIVE request
            primitiv
            e
S-GTreq     SS        S-TOKEN-GIVE request
            primitiv
            e
S-PTreq     SS        S-TOKEN-PLEASE request
            primitiv
            e
S-RELreq    SS        S-RELEASE request
            primitiv
            e
S-RELrsp+   SS        S-RELEASE response accept
            primitiv
            e
S-RELrsp-   SS        S-RELEASE response reject
            primitiv
            e
S-RSYNreq   SS        S-RESYNCHRONIZE request
            primitiv
            e
S-RSYNrsp   SS        S-RESYNCHRONIZE response
            primitiv
            e
S-SYNMreq   SS        S-SYNCHRONIZE-MAJOR request
            primitiv
            e
S-SYNMrsp   SS        S-SYNCHRONIZE-MAJOR response
            primitiv
            e
S-SYNmreq   SS        S-SYNCHRONIZE-MINOR request
            primitiv
            e
S-SYNmrsp   SS        S-SYNCHRONIZE-MINOR response
            primitiv
            e
S-UERreq    SS        S-U-EXCEPTION-REPORT request
            primitiv
            e
TC          PPDU      CAPABILITY DATA
TTC         PPDU      CAPABILITY DATA ACKNOWLEDGE
TD          PPDU      DATA
TE          PPDU      EXPEDITED DATA
TTD         PPDU      P-TYPED DATA


                          TABLE A-4/X.226
                         Specific Actions

Code                            Action

[01]  Mark presentation contexts proposed for definition which
      provider cannot support as ╥provider-rejection╙.
[02]  Set cr and rl to FALSE.
[03]  Record abstract and transfer syntaxes for the
      presentation contexts of the agreed DCS and for the
      default context.
[04]  Propose at least one transfer syntax for each
      presentation context.
[05]  Propose a transfer syntax for the default context if one
      is named in the request service primitive.
[06]  Select one transfer syntax for each presentation context
      agreed for definition and include the agreed presentation
      contexts in the DCS.
[07]  Set rl to TRUE.
[08]  If rl is TRUE then set cr to TRUE.
[09]  If aep is TRUE then:
      a)  set aep to FALSE; and
      b)  if FU(CR) is TRUE then the synchronization points
      associated with the last activity no longer have
      associated DCSs.
[10]  Record selected transfer syntax for each new presentation
      context and include new presentation contexts in the DCS.
[11]  Remove the presentation contexts agreed for deletion from
      the DCS.
[12]  Record FU(f) for f in fu-dom according to the
      presentation requirements in the CPA PPDU.
[13]  If FU(CR) then associate the DCS with the syncpoint
      identifier.
[14]  If FU(CR) and an activity is in progress, set the DCS to
      the inter-activity DCS.
[15]  Set aep to TRUE.
[16]  Set the DCS to that associated with the syncpoint
      identifier.
[17]  If FU(CR) then remember the DCS as the inter-activity
      DCS.
[18]  Set the DCS to that agreed during presentation-connection
      establishment.
[19]  Eliminate any associations between syncpoint serial
      number and the DCS for the current activity.
[20]  Set aep to FALSE.
[21]  Set the DCS as specified by the Presentation context
      identifier list parameter of the PPDU.
[22]  If FU(CR), then eliminate any associations between
      syncpoint identifiers and DCSs.


                          TABLE A-5/X.226
                            Predicates

Code                           Meaning

 p01  The presentation-connection is acceptable to the PPM
      (local matter).
 p02  If present, the named default context can be supported.
 p03  Each presentation data value is from a presentation
      context of the DCS proposed in the presentation-
      connection establishment, or from the default context if
      this DCS is empty.
 p04  Each presentation data value is from presentation
      contexts of the DCS being accepted in the presentation-
      connection establishment, or from the default context if
      this DCS is empty.
 p05  Each presentation data value is from presentation
      contexts of the DCS, or from the default context if the
      DCS is empty.
 p06  Each presentation data value is from presentation
      contexts of the DCS not proposed for deletion from the
      DCS by the peer PPM.
 p07  Each presentation data value is from presentation
      contexts of the DCS not proposed for deletion from the
      DCS by the local PPM.
 p08  The value of cr is TRUE.
 p09  Each presentation data value if from presentation
      contexts of the DCS not accepted for deletion from the
      DCS, or from presentation contexts accepted for addition
      to the DCS, or if no such presentation contexts are
      available, from the default context.
 p11  FU(CM) is TRUE.
 p13  Each presentation data value is from the default context.
 p14  FU(CM) is false, or FU(CM) is true and typed data
      functional unit was selected as a User session
      requirement.
 p15  Each presentation data value is from presentation
      contexts of the DCS which was agreed during presentation-
      connection establishment, or from the default context if
      this DCS is empty.
 p16  Each presentation data value is from presentation
      contexts of the DCS associated with the pair of Old
      activity identifier and Synchronization point serial
      number parameter values or from the default context when
      this DCS is empty.
 p17  FU(CR) is TRUE.
 p18  Each presentation date value is in presentation contexts
      of the DCS associated with the syncpoint identifier or
      from the default context if this DCS is empty.
 p19  Either no syncpoint identifier is associated with a DCS
      or the resync identifier is not associated with a DCS and
      is greater than the lowest syncpoint identifier which has
      an associated DCS.
 p20  The PPDU contains a Presentation context identifier list
      parameter.
 p21  Each presentation data value is from presentation
      contexts specified in the PPDU, or from the default
      context if no presentation contexts are specified in the
      PPDU.
 p22  For each presentation data value, an instance (chosen as
      a local matter) of encoding is supported by the PPM.
 p23  For each presentation data value the encoding is
      supported by the PPM.
 p24  Each presentation data value is from presentation
      contexts of the DCS, or from presentation contexts
      proposed for addition to the DCS by the local PPM, or
      from the default context if either the DCS is empty or
      all presentation contexts of the DCS were proposed for
      deletion by the local PPM.
 p25  Each presentation data value is from presentation
      contexts of the DCS not proposed for deletion by the peer
      PPM or from presentation contexts proposed for addition
      to the DCS by the local PPM.
 p26  The syncpoint identifier has an associated DCS.
 p27  Old session connection identifier parameter present.
 p28  There is a DCS associated with the pair of Old activity
      identifier and Synchronization point serial number
      parameters values.


                          TABLE A-6/X.226
                      Connexion Establishment

               STAI0         STAI1      STAI2
                idle         await      await
           no connection      CPA     P-CONrsp

P-CONreq  p02 & p03
          [04] [05] [02]
          [20]
          CP
          STAI1
CP        p01 & p02 & p03
          & p22
          [01] [02] [20]
          P-CONind
          STAI2
          ^p01 OR ^p02 OR
          ^p22
          [01]
          CPR
          STAI0
P-                                    p04
CONrsp+
                                      [06]
                                      [12]
                                      CPA
                                      STAt0
CPA                        p04
                           [03]
                           [12]
                           P-
                           CONcnf+
                           STAt0
P-CONrsp-                             p04
                                      [06]
                                      CPR
                                      STAI0
CPR                        p04
                           P-CONcnf-
                           STAI0
S-CONcnf-                  P-CONcnf-
                           STAI0


                          TABLE A-7/X.226
                    Connection release (normal)

             STAac0    STAac1     STAac2    STAt0
             await      await   await ACA connected
              ACA    P-ALTERrsp     or      - data
                                P-ALTERrsp transfer

P-RELreq   p07        p05         p07        p05
           [08] [07]  [08] [07]   [08] [07]  [08] [07]
           S-RELreq   S-RELreq    S-RELreq   S-RELreq
           STAac0     STAac1      STAac2     STAt0
S-RELind   p05        p06         p06        p05
           [08] [07]  [08] [07]   [08] [07]  [08] [07]
           P-RELind   P-RELind    P-RELind   P-RELind
           STAac0     STAac1      STAac2     STAt0
P-RELrsp+  p07 & ^p08 p05 & ^p08  p07 & ^p08 p05 & ^p08
           S-RELrsp+  S-RELrsp+   S-RELrsp+  S-RELrsp+
           STAI0      STAI0       STAI0      STAI0
           p07 & p08  p05 & p08   p07 & p08  p05 & p08
           [02]       [02]        [02]       [02]
           S-RELrsp+  S-RELrsp+   S-RELrsp+  S-RELrsp+
           STAt0      STAt0       STAt0      STAt0
S-RELcnf+  p05 & ^p08 p06 & ^p08  p06 & ^p08 p05 & ^p08
           P-RELcnf+  P-RELcnf+   P-RELcnf+  P-RELcnf+
           STAI0      STAI0       STAI0      STAI0
           p05 & p08  p06 & p08   p06 & p08  p05 & p08
           [02]       [02]        [02]       [02]
           P-RELcnf+  P-RELcnf+   P-RELcnf+  P-RELcnf+
           STAt0      STAt0       STAt0      STAt0
P-RELrsp-  p07        p05         p07        p05
           [02]       [02]        [02]       [02]
           S-RELrsp-  S-RELrsp-   S-RELrsp-  S-RELrsp-
           STAac0     STAac1      STAac2     STAt0
S-RELcnf-  p05        p06         p06        p05
           [02]       [02]        [02]       [02]
           P-RELcnf-  P-RELcnf-   P-RELcnf-  P-RELcnf-
           STAac0     STAac1      STAac2     STAt0


                          TABLE A-8/X.226
                    Connection release (abort)

           STAI1    STAI2    STAac0   STAac1   STAac2     STAt0
           await    await     await   await  await ACA  connected
            CPA    P-COMrsp    ACA      P-       or       - data
                                     ALTERrspP-ALTERrsp  transfer

P-UABreq p03       p03        p07       p05      p07        p05
         ARU       ARU        ARU       ARU      ARU        ARU
         STAI0     STAI0      STAI0     STAI0    STAI0      STAI0
ARU      p03 &     p03 & p21  p21 &     p06 &    p21 & p25  p05 & p21
        p21       & p23      p24       p21
         P-UABind  P-UABind   P-UABind  P-UABind P-UABind   P-UABind
         STAI0     STAI0      STAI0     STAI0    STAI0      STAI0
ARP      P-PABind  P-PABind   P-PABind  P-PABind P-PABind   P-PABind
         STAI0     STAI0      STAI0     STAI0    STAI0      STAI0
S-PABind P-PABind  P-PABind   P-PABind  P-PABind P-PABind   P-PABind
         STAI0     STAI0      STAI0     STAI0    STAI0      STAI0


                          TABLE A-9/X.226
                        Context Management

             STAac0    STAac1     STAac2     STAt0
             await      await   await ACA  connected
              ACA    P-ALTERrsp     or      - data
                                P-ALTERrsp transfer

P-ALTERreq            p05                    p05 & p11
                      [04]                   [04]
                      AC                     AC
                      STAac2                 STAac0
AC         p06                               p05 & p11
           [01]                              [01] [09]
           P-ALTERind                        P-ALTERind
           STAac2                            STAac1
P-ALTERrsp            p09         p09
                      [06] [11]   [06] [11]
                      ACA         ACA
                      STAt0       STAac0
ACA        p09                    p09 & p06
           [10] [11]              [10] [11]
           P-ALTERcnf             P-ALTERcnf
           STAt0                  STAac1


                         TABLE A-10/X.226
                           Data Transfer

             STAac0    STAac1     STAac2    STAt0
             await      await   await ACA connected
              ACA    P-ALTERrsp     or      - data
                                P-ALTERrsp transfer

P-DTreq    p07        p05         p07        p05
           TD         TD          TD         TD
           STAac0     STAac1      STAac2     STAt0
TD         p05        p06         p06        p05
           P-DTind    P-DTind     P-DTind    [09]
           STAac0     STAac1      STAac2     P-DTind
                                             STAt0
P-TDreq    p07 & p14  p05 & p14   p07 & p14  p05 & p14
           TTD        TTD         TTD        TTD
           STAac0     STAac1      STAac2     STAt0
TTD        p05 & p14  p06 & p14   p06 & p14  p05 & p14
           P-TDind    P-TDind     P-TDind    [09]
           STAac0     STAac1      STAac2     P-TDind
                                             STAt0
P-EXreq    p13        p13         p13        p13
           TE         TE          TE         TE
           STAac0     STAac1      STAac2     STAt0
TE         p13        p13         p13        p13
           P-EXind    P-EXind     P-EXind    [09]
           STAac0     STAac1      STAac2     P-EXind
                                             STAt0
P-CDreq    p07        p05         p07        p05
           TC         TC          TC         TC
           STAac0     STAac1      STAac2     STAt0
TC         p05        p06         p06        0
           P-CDind    P-CDind     P-CDind    [09]
           STAac0     STAac1      STAac2     P-CDind
                                             STAt0
P-CDrsp    p07        p05         p07        p05
           TCC        TCC         TCC        TCC
           STAac0     STAac1      STAac2     STAt0
TCC        p05        p06         p06        p05
           P-CDcnf    P-CDcnf     P-CDcnf    P-CDcnf
           STAac0     STAac1      STAac2     STAt0


                         TABLE A-11/X.226
                          Token Handling

             STAac0    STAac1     STAac2     STAt0
             await      await   await ACA  connected
              ACA    P-ALTERrsp     or      - data
                                P-ALTERrsp transfer

P-GTreq    S-GTreq    S-GTreq     S-GTreq    S-GTreq
           STAac0     STAac1      STAac2     STAt0
S-GTind    P-GTind    P-GTind     P-GTind    [09]
           STAac0     STAac1      STAac2     P-GTind
                                             STAt0
P-PTreq    p07        p05         p07        p05
           S-PTreq    S-PTreq     S-PTreq    S-PTreq
           STAac0     STAac1      STAac2     STAt0
S-PTind    p05        p06         p06        p05
           P-PTind    P-PTind     P-PTind    [09]
           STAac0     STAac1      STAac2     P-PTind
                                             STAt0
P-CGreq    S-CGreq    S-CGreq     S-CGreq    S-CGreq
           STAac0     STAac1      STAac2     STAt0
S-CGind    P-CGind    P-CGind     P-CGind    [09]
           STAac0     STAac1      STAac2     P-CGind
                                             STAt0


                         TABLE A-12/X.226
                          Synchronization

             STAac0    STAac1     STAac2    STAt0
             await      await   await ACA connected
              ACA    P-ALTERrsp     or      - data
                                P-ALTERrsp transfer

P-SYNmreq  ^p17 & p07 p05         ^p17 & p07 p05
           S-SYNmreq  S-SYNmreq   S-SYNmreq  S-SYNmreq
           STAac0     [13]        STAac2     [13]
                      STAac1                 STAt0
P-SYNmind  p05        ^p17 & p06  ^p17 & p06 p05
           P-SYNmind  P-SYNmind   P-SYNmind  P-SYNmind
           [13]       STAac1      STAac2     [13]
           STAac0                            STAt0
P-SYNmrsp  p07        p05         p07        p05
           S-SYNmrsp  S-SYNmrsp   S-SYNmrsp  S-SYNmrsp
           STAac0     STAac1      STAac2     STAt0
S-SYNmcnf  p05        p06         p06        p05
           P-SYNmcnf  P-SYNmcnf   P-SYNmcnf  P-SYNmcnf
           STAac0     STAac1      STAac2     STAt0
P-SYNMreq  ^p17 & p07 p05         ^p17 & p07 p05
           S-SYNMreq  S-SYNMreq   S-SYNMreq  S-SYNMreq
           STAac0     STAac1      STAac2     STAt0
S-SYNMind  p05        ^p17 & p06  ^p17 & p06 p05
           P-SYNMind  P-SYNMind   P-SYNMind  P-SYNMind
           STAac0     STAac1      STAac2     STAt0
P-SYNMrsp  p07        ^p17 & p05  ^p17 & p07 p05
           S-SYNMrsp  S-SYNMrsp   S-SYNMrsp  S-SYNmrsp
           [22] [13]  STAac1      STAac2     [22] [13]
           STAac0                            STAt0
S-SYNcnf   ^p17 & p05 p06         ^p17 & p06 p05
           P-SYNMcnf  P-SYNMcnf   P-SYNMcnf  P-SYNMcnf
           STAac0     [22] [13]   STAac2     [22] [13]
                      STAac1                 STAt0


                         TABLE A-13/X.226
            Activity Management and Exception Handling

            STAac0           STAac1      STAac2       STAt0
            await            await        await connected - data
             ACA           P-ALTERrsp    ACA or     transfer
                                           P-
                                         ALTERrs
                                            p

P-     ^p17 & p07       p05                ^p17 &  p05
ACTSre                                   p07
q
       S-ACTSreq        [17]               S-      [17]
                                        ACTSreq
       STAac0           S-ACTSreq          STAac2  S-ACTSreq
                        STAac1                     STAt0
S-     p05              ₧p17 & p06         ^p17 &  p05
ACTSin                                   p06
d
       [09] [17]        P-ACTSind          P-      [09] [17]
                                        ACTSind
       P-ACTSind        STAac1             STAac2  P-ACTSind
       STAac0                                      STAt0
P-     ^p17 & p07       p05                ^p17 &  p05
ACTEre                                   p07
q
       S-ACTEreq        S-ACTEreq          S-      S-ACTEreq
                                        ACTEreq
       STAac0           STAac1             STAac2  STAt0
S-     p05              ₧p17 & p06         ^p17 &  p05
ACTEin                                   p06
d
       P-ACTEind        P-ACTEind          P-      P-ACTEind
                                        ACTEind
       STAac0           STAac1             STAac2  STAt0
P-     p07              ^p17 & p05         ^p17 &  p05
ACTErs                                   p07
p
       [14] [15]        S-ACTErsp          S-      [14] [15]
                                        ACTErsp
       S-ACTErsp        STAac1             STAac2  S-ACTErsp
       STAac0                                      STAt0
S-     ^p17 & p05       p06                ^p17 &  p05
ACTEcn                                   p06
f
       P-ACTEcnf        [14] [19]          P-      [14] [19]
                                        ACTEcnf
       STAac0           P-ACTEcnf          STAac2  P-ACTEcnf
                        STAac1                     STAt0
P-     S-ACTIreq        S-ACTIreq          S-      S-ACTIreq
ACTIre                                   ACTIreq
q
       STAt0            STAt0              STAt0   STAt0
S-     [20]             [20]               [20]    [20]
ACTIin
d
       P-ACTIind        P-ACTIind          P-      P-ACTIind
                                        ACTIind
       STAt0            STAt0              STAt0   STAt0
P-                                                 [14]
ACTIrs
p
                                                   S-ACTIrsp
                                                   STAt0
S-                                                 [14]
ACTIcn
f
                                                   P-ACTIcnf
                                                   STAt0
P-     ^p17 & p07       (^p17 OR p27 OR    ^p17 &  (^p17 OR p27 OR
ACTRre                 ₧p28) & p05        p07     ₧p28) & p05
q
       S-ACTRreq        S-ACTRreq          S-      S-ACTRreq
                                        ACTRreq
       STAac0           STAac1             STAac2  STAt0
                        ₧p27 & p28 & p17           ^p27 & p28 & p17
                      & p16                     & p16
                        [17] [16]                  [17] [16]
                        S-ACTRreq                  S-ACTRreq
                        STAac1                     STAt0
S-     (^p17 OR p27 OR  ^p17 & p06         ^p17 &  (^p17 OR p27 OR
ACTRin ₧p28) & p05                        p06     ₧p28) & p05
d
       [09]             P-ACTRind          P-      [09]
                                        ACTRind
       P-ACTRind        STAac1             STAac2  P-ACTRind
       STAac0                                      STAt0
       ^p27 & p28 &                                ^p27 & p28 & p17
      p17 & p16                                 & p16
       [09] [17] [16]                              [09] [17] [16]
       P-ACTRind                                   P-ACTRind
       STAac0                                      STAt0


                   TABLE A-13/X.226 (continued)
            Activity Management and Exception Handling

            STAac0           STAac1      STAac2       STAt0
            await            await        await connected - data
             ACA           P-ALTERrsp    ACA or     transfer
                                           P-
                                         ALTERrs
                                            p

P-     S-ACTDreq        S-ACTDreq          S-      S-ACTDreq
ACTDre                                   ACTDreq
q
       STAt0            STAt0              STAt0   STAt0
S-     [09]             [09]               [09]    [09]
ACTDin
d
       P-ACTDind        P-ACTDind          P-      P-ACTDind
                                        ACTDind
       STAt0            STAt0              STAt0   STAt0
P-                                                 [14] [19]
ACTDrs
p
                                                   S-ACTDrsp
                                                   STAt0
S-                                                 [14] [19]
ACTDcn
f
                                                   P-ACTDcnf
                                                   STAt0
P-     p07              p05                p07     p05
UERreq
       S-UERreq         S-UERreq           S-      S-UERreq
                                        UERreq
       STAt0            STAt0              STAt0   STAt0
S-     p05              p06                p06     p05
UERind
       P-UERind         P-UERind           P-      P-UERind
                                        UERind
       STAt0            STAt0              STAt0   STAt0
S-     P-PERind         P-PERind           P-      P-PERind
PERind                                   PERind
       STAt0            STAt0              STAt0   STAt0


                         TABLE A-14/X.226
                         Resynchronization

           STAac0         STAac1        STAac2           STAt0
            await         await      await ACA or   connected - data
             ACA        P-ALTERrsp    P-ALTERrsp        transfer

P-                                                   ₧p11 & p05
RSYNre
q
                                                     RS
                                                     STAt0
       ^p17 & p07      ^p17 & p05     ^p17 & p07     p11 & ^p17 & p05
       RS              RS              RS            RS
       STAt0           STAt0           STAt0         STAt0
       p17 & p19 &     p17 & p19 &    p17 & p19 &    p11 & p17 & p19 &
      p07             p05            p07            p05
       RS              RS             RS             RS
       STAt0           STAt0          STAt0          STAt0
       p17 & p26 &     p17 & p26 &    p17 & p26 &    p11 & p17 & p26 &
      p18             p18            p18            p18
       RS              RS             RS             RS
       STAt0           STAt0          STAt0          STAt0
       p17 & ^p19 &    p17 & ^p19 &   p17 & ^p19 &   p11 & p17 & ^p19 &
      ^p26 & p15      ^p26 & p15     ^p26 & p15     ^p26 & p15
       [18]            [18]           [18]           [18]
       RS              RS             RS             RS
       STAt0           STAt0          STAt0          STAt0
RS                                                   ^p11 & p05
                                                     P-RSYNind
                                                     STAt0
       ^p17 & p21      ₧p17 & p21     ^p17 & p21     p11 & ^p17 & p21
       [21]                           [21]           P-RSYNind
       P-RSYNind       P-RSYNind      P-RSYNind
       STAt0           STAt0          STAt0          STAt0
       p17 & p19 &     p17 & p19 &    p17 & p19 &    p11 & p17 & p19 &
      p21             p21            p21            p21
       [21]                           [21]           P-RSYNind
       P-RSYNind       P-RSYNind      P-RSYNind
       STAt0           STAt0          STAt0          STAt0
       p17 & p26 &     p17 & p26 &    p17 & p26 &    p11 & p17 & p26 &
      p18             p18            p18            p18
       [16]            [16]           [16]           [16]
       P-RSYNind       P-RSYNind      P-RSYNind      P-RSYNind
       STAt0           STAt0          STAt0          STAt0
       p17 & ^p19 &    p17 & ^p19 &   p17 & ^p19 &   p11 & p17 & ^p19 &
      ^p26 & p15      ^p26 & p15     ^p26 & p15     ^p26 & p15
       [18]            [18]           [18]           [18]
       P-RSYNind       P-RSYNind      P-RSYNind      P-RSYNind
       STAt0           STAt0          STAt0          STAt0
P-                                                   ^p11 & p05
RSYNrs
p
                                                     RSA
                                                     STAt0
                                                     p11 & ^p17 & p05
                                                     RSA
                                                     STAt0
                                                     p11 & p17 & p19 &
                                                  p05
                                                     RSA
                                                     STAt0
                                                     p11 & p17 & p26 &
                                                  p05
                                                     RSA
                                                     STAt0
                                                     p11 & p17 & ^p19 &
                                                  ^p26 & p05
                                                     RSA
                                                     STAt0


                   TABLE A-14/X.226 (continued)
                         Resynchronization

           STAac0         STAac1        STAac2           STAt0
            await         await      await ACA or   connected - data
             ACA        P-ALTERrsp    P-ALTERrsp        transfer

RSA                                                  ^p11 & p05
                                                     P-RSYNcnf
                                                     STAt0
                                                     p11 & ^p17 & p21
                                                     [21]
                                                     P-RSYNcnf
                                                     STAt0
                                                     p11 & p17 & p19 &
                                                  p21
                                                     [21]
                                                     P-RSYNcnf
                                                     STAt0
                                                     p11 & p17 & p26 &
                                                  p05
                                                     P-RSYNcnf
                                                     STAt0
                                                     p11 & p17 & ^p19 &
                                                  ^p26 & p05
                                                     P-RSYNcnf
                                                     STAt0

                            Appendix I

                     (to Recommendation X.226)

             Differences between Recommendation X.226

                and ISO International Standard 8823

I.1   Recommendation  X.226  contains no statement  concerning  the
relative  precedence of any section or annex.  ISO/IEC  JTC  1  has
indicated its intention to add a statement, prior to publication of
ISO 8823, concerning precedence.

Blanc



_______________________________

1 Recommendation X.226 and ISO 8823 [Information processing systems
-  Open  Systems Intrconnection - Connection oriented  presentation
protocol  specification] were developed in close collaboration  and
are  technically  aligned,  except for  the  differences  noted  in
Appendix I

2  The  implementation  and  use of this  Recommendation  for  Open
Systems Interconnection requires the public assignment of values of
ASN.1 type OBJECT IDENTIFIER to specifications of abstract syntaxes
and  transfer syntaxes. Public specification and naming of abstract
syntaxes and transfer syntaxes can occur in ISO standards or  CCITT
Recommendations,  or  under  the  mechanisms  identified   in   the
Registration   Authority   procedures.  A  Registration   Authority
procedures specification is under development.

3 At present at the stage of draft.