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InfoMagic Standards 1994 January
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1988
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.\" Troff code generated by TPS Convert from ITU Original Files
.\" Not Copyright ( c) 1991
.\"
.\" Assumes tbl, eqn, MS macros, and lots of luck.
.TA 1c 2c 3c 4c 5c 6c 7c 8c
.ds CH
.ds CF
.EQ
delim @@
.EN
.nr LL 40.5P
.nr ll 40.5P
.nr HM 3P
.nr FM 6P
.nr PO 4P
.nr PD 9p
.po 4P
.rs
\v | 5i'
.sp 1P
.ce 1000
\v'12P'
\s12PART\ V
\v'4P'
.RT
.ce 0
.sp 1P
.ce 1000
\fBI.500\(hySeries Recommendations\fR \v'2P'
.ce 0
.sp 1P
.ce 1000
\fBINTERNETWORK\ INTERFACES\fR
.ce 0
.sp 1P
.LP
.rs
.sp 31P
.ad r
Blanc
.ad b
.RT
.LP
.bp
.LP
\fBMONTAGE: PAGE 2 = PAGE BLANCHE\fR
.sp 1P
.RT
.LP
.EF '% Fascicle\ III.9\ \(em\ Rec.\ I.500''
.OF '''Fascicle\ III.9\ \(em\ Rec.\ I.500 %'
.LP
.bp
.sp 2P
.LP
\fBRecommendation\ I.500\fR
.RT
.sp 2P
.sp 1P
.ce 1000
\fBGENERAL\ STRUCTURE\ OF\ THE\ ISDN\ INTERWORKING\ RECOMMENDATIONS\fR
.EF '% Fascicle\ III.9\ \(em\ Rec.\ I.500''
.OF '''Fascicle\ III.9\ \(em\ Rec.\ I.500 %'
.ce 0
.sp 1P
.ce 1000
\fI(Melbourne, 1988)\fR
.sp 9p
.RT
.ce 0
.sp 1P
.LP
\fB1\fR \fBIntroduction\fR
.sp 1P
.RT
.PP
An ISDN is a network, in general evolving from a telephony
Integrated Digital Network, that provides end\(hyto\(hyend digital connectivity
to
support a wide range of services, including voice and non\(hyvoice services, to
which users have access by a limited set of standard multi\(hypurpose user
network interfaces. In contrast, existing dedicated networks have always
been developed for specific (types of) services. Therefore, especially
in the initial phase, the ISDN may support many services which in principle
are still existent in
dedicated networks. Thus, it is necessary to provide interworking between
ISDN and dedicated networks to allow communication between terminals belonging
to equivalent services offered through different networks.
.PP
There will be a need for interworking functions (IWF) between ISDN and
dedicated networks to cope with the different environments given by the
various networks. The structure of these IWFs showing the functions necessary
for the mapping should be uniform to permit, if possible, a common use
of
functional parts in several IWFs. Detailed description of these IWFs, which
(as far as is possible), should permit conveyance of ISDN features through
existing networks, is given in the I.500\(hySeries of Recommendations.
.PP
The I.500\(hySeries of Recommendations deal with network aspects of
interworking.
.RT
.sp 2P
.LP
\fB2\fR \fBOrganization of ISDN interworking Recommendations\fR
.sp 1P
.RT
.PP
Figure\ 1/I.500 shows the organization of the ISDN interworking
Recommendations contained in the I.500\(hySeries Recommendations, and the
relationship with other Recommendations. The Recommendations in Figure\
1/I.500 have been grouped by level of detail into:
.RT
.LP
\(em
general level;
.LP
\(em
scenario level;
.LP
\(em
functional level;
.LP
\(em
protocol level.
.sp 1P
.LP
2.1
\fIGeneral level\fR
.sp 9p
.RT
.PP
Recommendations I.500 and I.510 form the general level, i.e., the basis
for Recommendations in the scenario and functional levels.
.PP
Recommendation I.500 describes the organization of the (ISDN
interworking) Recommendations and the structure of the I.500\(hySeries of
Recommendations, whilst I.510 sets out the ISDN interworking
principles.
.RT
.sp 1P
.LP
2.2
\fIScenario level\fR
.sp 9p
.RT
.PP
The scenario level of Recommendations describes the general
arrangements for interworking between ISDN and ISDN, and between ISDN and
dedicated networks. Recommendation\ I.515 specifying the parameter exchange
which may be necessary for interworking situations, is also located at the
scenario level.
.RT
.sp 1P
.LP
2.3
\fIFunctional level\fR
.sp 9p
.RT
.PP
The detailed level is formed by those Recommendations that are
specifying the interworking functional requirements of the interworking
scenarios shown in the scenario level Recommendations.
.RT
.sp 1P
.LP
2.4
\fIProtocol level\fR
.sp 9p
.RT
.PP
In the protocol level, the protocols listed are those that appear at the
reference points K\dx\uand\ N\dx\u.
.PP
\fINote\fR \ \(em\ ISDN interworking related subjects that correspond to the
above four levels are also dealt with in the Recommendations\ I.310, I.324,
I.340, X.300 and\ X.301. Recommendation\ I.310 defines the interworking
reference points and an outline description of IWF.
.bp
.PP
Recommendation I.340 defines ISDN Connection Types.
.PP
Recommendations\ X.300 and X.301 give the guiding principles and
functions for interworking between networks offering data services described
in Recommendations\ X.1 and\ X.10.
.RT
.PP
2.5
Recommendations which relate to interworking are shown in
Figure\ 1/I.500 and are assigned to the levels listed in \(sc\ 2. As the
contents of some Recommendations cover more than one level, these Recommendations
appear at each level to which they relate.
.sp 9p
.RT
.LP
.rs
.sp 30P
.ad r
\fBFigure 1/I.500, (N), p.\fR
.sp 1P
.RT
.ad b
.RT
.sp 2P
.LP
\fB3\fR \fBReferences\fR
.sp 1P
.RT
.PP
The references are general to all I.500 Recommendations and are to be read
in conjunction with Figure\ 1/I.500, where the organization of ISDN
interworking Recommendations is shown.
.RT
.sp 1P
.LP
3.1
\fIInterworking\fR
.sp 9p
.RT
.PP
X.300\(hySeries
Interworking between public networks, and
between public networks and other networks for the provision
of data transmission services
.RT
.LP
I.324
ISDN architecture functional model
.LP
I.340
Connection types/elements for ISDN\(hyISDN
interworking
.LP
X.31
Support of packet\(hymode terminal equipment by
an ISDN
.LP
X.81
Interworking between an ISDN circuit switched and a
circuit switched public data network
(CSPDN)
.bp
.sp 1P
.LP
3.2
\fIServices and network capabilities\fR
.sp 9p
.RT
.PP
X.1
International user classes of service in public data
networks and integrated services digital networks
(ISDNs)
.RT
.LP
X.2
International data transmission services and
optional user facilities in public data networks
and ISDNs
.LP
X.10
Categories of access for data terminal equipment
(DTE) to public data transmission services
.LP
I.122
Framework for providing additional packet\(hymode
bearer services
.LP
I.200\(hySeries
Service aspects supported by an ISDN
.LP
I.310
ISDN \(em Network functional principles
.LP
I.320
ISDN protocol reference model
.LP
I.325
Reference configurations for ISDN connection types
.LP
I.411
ISDN user\(hynetwork interfaces \(em reference
configurations
.LP
I.412
ISDN user\(hynetwork interfaces \(em
Interface structures and access capabilities
.LP
I.420
Basic rate user\(hynetwork interface
.LP
I.421
Primary rate user\(hynetwork interface
.LP
I.441
.LP
(Q.921)
\-v'10p'
ISDN user\(hynetwork interface data link
layer specification
\v'10p'
.LP
I.451
.LP
(Q.931)
\-v'10p'
ISDN user\(hynetwork interface
layer\ 3 specification
\v'10p'
.sp 1P
.LP
3.3
\fISignalling\fR
.sp 9p
.RT
.PP
Q.700
Network protocols (MTP, ISUP, etc.)
.RT
.LP
Q.120\(hyQ.180
Specification of Signalling Systems No.\ 4
and No.\ 5
.LP
Q.251\(hyQ.300
Specification of Signalling System No.\ 6
.LP
Q.310\(hyQ.490
Specification of Signalling Systems R1
and R2
.LP
X.25
Interface between data terminal equipment (DTE) and
data circuit equipment (DCE) for terminals operating in
the packet\(hymode and connected to public data networks
by dedicated circuits
.LP
X.71
Decentralized terminal and transit control signalling
system on international circuits between synchronous
data networks
.LP
X.75
Packet switched signalling system between public
networks providing data transmission
services
.LP
U.12
Terminal and transit control signalling system for telex
and similar services on international circuits (type\ D
signalling)
.sp 1P
.LP
3.4
\fIRate adaptation\fR
.sp 9p
.RT
.PP
I.460
Multiplexing, rate adaptation and support of existing
interfaces
.RT
.LP
I.461
.LP
(X.30)
\-v'10p'
Support of X.21, X.21 | fIbis\fR | and
X.20 | fIbis\fR | based DTEs by an ISDN
\v'10p'
.LP
I.462
.LP
(X.31)
\-v'10p'
Support of packet\(hymode terminal
equipment by an ISDN
\v'10p'
.LP
I.463
.LP
(V.110)
\-v'10p'
Support of DTEs with V\(hySeries
type interfaces by an ISDN
\v'10p'
.LP
I.464
Multiplexing, rate adaptation and support of
existing interfaces for restricted 64\ kbit/s
transfer capability
.LP
I.465
.LP
(V.120)
\-v'10p'
Support by ISDN of DTEs with V\(hySeries
type interfaces with provision for statistical
multiplexing
.bp
.sp 1P
.LP
3.5
\fINumbering\fR
.sp 9p
.RT
.PP
X.121
International numbering plan for public data
networks
.RT
.LP
X.122
Numbering plan interworking between a Packet Switched
Public Data Network (PSPDN) and an Integrated Services
Digital Network (ISDN) or Public Switched Telephone Network
(PSTN) in the short\(hyterm
.LP
I.331
.LP
(E.164)
\-v'10p'
Numbering plan for the ISDN era
\v'10p'
.LP
E.166
Numbering plan interworking in the ISDN era
.LP
I.330
ISDN numbering and addressing principles
.LP
I.332
Numbering principles for interworking between
ISDNs and dedicated networks with different numbering
plans
.LP
F.69
Plan for telex destination codes
.sp 2P
.LP
\fBRecommendation\ I.510\fR
.RT
.sp 2P
.sp 1P
.ce 1000
\fBDEFINITIONS\ AND\ GENERAL\ PRINCIPLES\ FOR\ ISDN\ INTERWORKING\fR
.EF '% Fascicle\ III.9\ \(em\ Rec.\ I.510''
.OF '''Fascicle\ III.9\ \(em\ Rec.\ I.510 %'
.ce 0
.sp 1P
.ce 1000
\fI(Melbourne, 1988)\fR
.sp 9p
.RT
.ce 0
.sp 1P
.LP
\fB1\fR \fBIntroduction\fR
.sp 1P
.RT
.PP
This Recommendation sets forth the general principles for
interworking between ISDNs, between ISDNs and other networks, and internal
to an ISDN. The need for interworking stems from the coexistence of existing
dedicated networks with ISDNs and from the use of different, yet compatible,
bearer services or teleservices for the provision of an end\(hyto\(hyend
telecommunication service. When ISDNs are introduced, it is to be expected
that most users will need to interwork with the users of other networks,
especially public switched telephone networks (PSTNs), public land mobile
networks (PLMNs) and dedicated data networks.
.PP
Normally, each instance of communication within an ISDN will take
place between the users of services with identical attribute values. However,
communication may also take place between users of services with non\(hyidentical
attribute values. In these cases interworking functions (IWFs) will be
required. In general, when an ISDN user communicates with the user of another
network, if the service perceived by the user of that other network were
to be defined by the attribute method, the values would not be identical
to those of the ISDN user.
.PP
The purpose of interworking is to enable the users of \*Qdifferent\*U
services on an ISDN to establish a useful communication or for an ISDN
user to establish a useful communication with a user of another network
and vice\(hyversa. The term \*Qservice\*U in this Recommendation implies
a telecommunication service as defined in Recommendation\ I.210.
.PP
To permit interworking, interworking capabilities, making use of
IWFs, may be required in one or more of the following:
.RT
.LP
\(em
the ISDN,
.LP
\(em
any other network involved,
.LP
\(em
customer equipment.
.sp 2P
.LP
\fB2\fR \fBScope\fR
.sp 1P
.RT
.PP
This Recommendation contains the definitions and general principles to
be applied in instances of ISDN interworking, which include interworking
between ISDNs, between ISDNs and other networks, and internal to
an\ ISDN.
.bp
.PP
The ISDN interworking configurations to be considered within the scope
of this Recommendation include the interconnection of two networks where
at
least one network is an ISDN, the concatenation of more than two networks
where an ISDN interconnects other networks (as a transit network), or the
interconnection of two ISDNs by one or more other networks.
.PP
ISDN interworking, as defined in this Recommendation, is
considered to take place whenever end\(hyto\(hyend communication has to be
provided:
.RT
.LP
a)
between different networks where at least one network
is an ISDN, or
.LP
b)
between telecommunication services with different lower or
higher layer attributes or both, where at least one of the
interworking telecommunication service is supported by the
ISDN, or
.LP
c)
between different networks and between telecommunication
services with different lower or higher layer service
attributes, or both.
.PP
ISDN interworking, as defined in this Recommendation, is intended to cover
both voice and non\(hyvoice applications.
.PP
\fINote\fR \ \(em\ Interworking at layers above layer\ 3 of the OSI model
is not generally specified within this Recommendation and is for further
study.
.RT
.sp 2P
.LP
\fB3\fR \fBAbbreviations\fR
.sp 1P
.RT
.PP
CCSN
Common channel signalling network
(SS\ No.7)
.RT
.LP
CE
Connection element
.LP
CS
Circuit switched
.LP
CSPDN
Circuit switched public data network
.LP
DTE
Data terminal equipment
.LP
ISDN
Integrated Services Digital Network
.LP
IWF
Interworking function
.LP
OSI
Open Systems Interconnection
.LP
PDN
Public data network
.LP
PH
Packet handler
.LP
PLMN
Public land mobile network
.LP
PS
Packet switched
.LP
PSPDN
Packet switched public data network
.LP
PSTN
Public switched telephone network
.LP
SS\ No.7
Signalling System No.\ 7
.LP
TA
Terminal adaptor
.LP
TE
Terminal equipment
.sp 2P
.LP
\fB4\fR \fBDefinitions\fR
.sp 1P
.RT
.sp 1P
.LP
4.1
\fIDefinitions related to services and network capabilities\fR
.sp 9p
.RT
.PP
The definitions which follow are related to services and to
network capabilities. In those instances where terms already are
defined in other Recommendations, appropriate references are made to such
Recommendations.
.PP
The following definitions apply to ISDN interworking:
.PP
\fITelecommunication service\fR , as defined in Recommendation I.210.
.PP
\fIBearer service in the ISDN\fR , as defined in Recommendation I.210 and
in the I.230\(hySeries.
.PP
\fITeleservice\fR , as defined in Recommendation\ I.210 and in the
I.240\(hySeries, provides the full capacity for communication through
terminal and network lower and higher layer functions.
.PP
\fIBearer service in dedicated networks:\fR | The term \fIbearer service\fR
| in dedicated networks is characterized by a set of lower layer attributes
(e.g.\ data transmission services, as defined in Recommendation\ X.1, for
use in public data networks) and corresponds to the term \fIbearer service\fR
in an ISDN. Examples of \fIbearer services\fR in dedicated networks are
data transmission over a data network and data transmission over the telephone
network.
.bp
.PP
\fISupplementary service\fR , as defined in Recommendation I.210 and in
the I.250 Series.
.PP
\fIBearer capability\fR , as defined in Recommendation I.210, specifies
the technical features of a \fIbearer service\fR in an ISDN as these appear
to a user at the access point (S/T\ reference point). The term \fIbearer
capability\fR also
may be used with respect to dedicated networks. A \fIbearer capability\fR
does not include any terminal functions.
.RT
.sp 1P
.LP
4.2
\fIDefinitions related to general ISDN interworking configurations\fR
.sp 9p
.RT
.PP
This section provides concepts and definitions of terms relevant to the
general ISDN interworking configuration. Figure\ 1/I.510 depicts the scope
of application of several key terms.
.RT
.LP
.rs
.sp 25P
.ad r
\fBFigure 1/I.510, (N), p.\fR
.sp 1P
.RT
.ad b
.RT
.PP
In accordance with Figure 1/I.510, the following terms are
defined:
.sp 1P
.LP
\fBinterworking\fR
.sp 9p
.RT
.PP
Within the scope of the I.500\(hySeries of Recommendations, the term \fIinterworking\fR
| is used to express interactions between networks, between end systems,
or between parts thereof, with the aim of providing a functional
entity capable of supporting an end\(hyto\(hyend communication. The interactions
required to provide a functional entity rely on functions and on the means
to select these functions.
.RT
.sp 1P
.LP
\fBinterworking functions (IWFs)\fR
.sp 9p
.RT
.PP
The functions referred to in the Interworking definition above,
which include the conversion of physical and electrical states and the
mapping of protocols. An IWF may be implemented in the ISDN, in the other
network(s), at the user's premises, through a third\(hyparty service provider,
or in some
combination of these.
.bp
.PP
The IWFs needed as a result of a service requirement for
interworking are categorized as
connection\(hydependent IWFs
or
communication\(hydependent IWFs
. The relationships among these
terms and definitions for connection\(hydependent IWFs and for
communication\(hydependent IWFs are contained in
Figure\ 2/I.510.
.RT
.LP
.rs
.sp 25P
.ad r
\fBFigure 2/I.510, (N), p.\fR
.sp 1P
.RT
.ad b
.RT
.sp 2P
.LP
\fB5\fR \fBTelecommunication services to be supported by ISDN\fR
\fBinterworking configurations\fR
.sp 1P
.RT
.PP
This section contains a list of telecommunication services that are supported
by interconnections between ISDNs and between ISDNs and other
networks and defines the types of interworking functions required.
The concept of \(sc\ 5 take into account:
.RT
.LP
a)
the definitions as outlined in \(sc\ 4;
.LP
b)
existing networks to be interconnected with ISDN
(ISDNs, PSTNs, CSPDNs, PSPDNs, others);
.LP
c)
services to be offered with the ISDN and through
interworking with ISDN.
.PP
End\(hyto\(hyend communication
may require:
.LP
i)
interworking at lower layers;
.LP
ii)
interworking at higher layers;
.LP
iii)
interworking at both lower and higher
layers.
.PP
Table 1/I.510 displays the networks that support telecommunication services
which are also supported by an ISDN and which are candidates,
therefore, for interworking with an ISDN in the provision of one of those
telecommunication services. Furthermore, Table\ 1/I.510 depicts the type of
interworking functions that may be required for each interworking
configuration. Note that the table does not indicate the possibility for
interworking between different telecommunication services
(e.g.\ telex\(hyto\(hyTeletex).
.bp
.ce
\fBH.T. [T1.510]\fR
.ce
TABLE\ 1/I.510
.ce
\fBNetwork support of telecommunication services\fR
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(90p) | cw(18p) sw(18p) sw(18p) sw(18p) sw(18p) sw(48p) , ^ | c | c | c | c | c | c.
{
Telecommunication services
supported by the ISDN
} ISDN interconnected with
ISDN PSTN CSPDN PSPDN Telex Other dedicated networks
_
.T&
lw(90p) | cw(18p) | cw(18p) | cw(18p) | cw(18p) | cw(18p) | cw(48p) .
Telephony 0 N \(em \(em \(em N
_
.T&
lw(90p) | cw(18p) | cw(18p) | cw(18p) | cw(18p) | cw(18p) | cw(48p) .
{
Data transmission (see Note 2)
} (L) N, | N, | L) N, | L) \(em N, | L)
_
.T&
lw(90p) | cw(18p) | cw(18p) | cw(18p) | cw(18p) | cw(18p) | cw(48p) .
Telex 0 \(em \(em \(em N, | N, |
_
.T&
lw(90p) | cw(18p) | cw(18p) | cw(18p) | cw(18p) | cw(18p) | cw(48p) .
Teletex 0 N, | N, | N, | \(em N, | , |
_
.T&
lw(90p) | cw(18p) | cw(18p) | cw(18p) | cw(18p) | cw(18p) | cw(48p) .
Fascimile 0 N, | N, | N, | \(em N, |
.TE
.LP
0
No interworking functions foreseen
.LP
N
Connection\(hydependent interworking needed
.LP
L
Lower layer communication\(hydependent interworking
needed
.LP
H
Higher layer communication\(hydependent interworking
needed
.LP
(\ )
N/L/H may be needed
.LP
\fINote\ 1\fR
\ \(em\ The list of services in Table 1/I.510 is not
exhaustive and is therefore for further study. In particular,
bearer services must be included.
.LP
\fINote\ 2\fR
\ \(em\ See Recommendation X.1 for a description of data
transmission services.
.LP
\fINote\ 3\fR
\ \(em\ It is assumed for Table 1/I.510 that, for the cases
of ISDN\(hyto\(hyISDN interworking, the telecommunication services
listed above are supported in both ISDNs by the same bearer,
no interworking functions are therefore required. ISDN\(hyto\(hyISDN
interworking situations that involve different bearers, as
an extension of Table\ 1/I.510, are for further
study.
.nr PS 9
.RT
.ad r
\fBTableau 1/I.510 [T1.510], p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.sp 1
.sp 2P
.LP
\fB6\fR \fBISDN interworking configurations\fR
.sp 1P
.RT
.PP
This section contains the general interworking reference
configurations that form the basis of all possible ISDN interworking
configurations covered by the I.500\(hySeries of Recommendations.
.PP
The configurations are entirely functional and do not serve any aspect
of the interworking function(s) needed in any specific instance of
interworking. The complexities of specific cases are considered in the
Recommendations that deal at a scenario level of detail with the individual
types of networks with which an ISDN may be interconnected,
i.e.\ Recommendations\ I.520, I.530,\ etc.
.PP
The network interworking reference point is the K\dx\uor \dx\ureference
point when the network directly interconnected to the ISDN is a
non\(hyISDN or an ISDN, respectively.
.RT
.sp 1P
.LP
6.1
\fIReference points for network interconnections\fR
.sp 9p
.RT
.PP
The protocol reference model for ISDN interworking is outlined in \(sc\
5 of Recommendation\ I.320.
.PP
The reference points K\dx\uand N\dx\ufor network interconnections are defined
in Recommendation\ I.324, \(sc\ 4.2.4.
.bp
.PP
According to Note 1 to Figure\ 8/I.324 the value x\ =\ 1 signifies that
interworking functions exist in the ISDN. The value x\ =\ 2 signifies that
no
interworking functions are required in the ISDN. No assumption is made
regarding interworking functions outside the ISDN. Regardless of the value
of x, the possibility of interworking functions in the other networks,
between the networks, or of some combination of these situations, is kept
open. The case of N\d1\ucovers the situation when interworking functions
are split between the
two ISDNs involved.
.RT
.sp 1P
.LP
6.1.1
\fIInterworking using one\(hystage selection (one\(hystage\fR
\fIinterworking)\fR
.sp 9p
.RT
.PP
Interworking using one\(hystage selection is possible when the
interconnection of networks takes place by interconnecting trunk lines.
It is also possible when the networks are physically inseparable [for example,
see
b) of Figure\ 6/I.510, and associated text]. In this type of interworking,
each of the terminals involved in a communication has assigned to it a
directory
number from the numbering plan of the network to which it is connected. For
call establishment, one\(hystage selection is assumed. An example of this
type of interworking is the interconnection of a CSPDN using X.71 interexchange
signalling and an ISDN using SS\ No.\ 7 interexchange signalling.
.PP
For interworking by one\(hystage selection, the interconnection of
networks takes place at reference points K\dx\uor \dx\u(see
Figure\ 3/I.510).
.PP
The application of existing interfaces and the specification of new
interfaces at the K\dx\uand N\dx\ureference points for interworking by
one\(hystage selection needs further study.
.PP
\fINote\fR \ \(em\ In Recommendation X.300 this category of interworking is
defined as \*Qinterworking by call control mapping\*U (see \(sc\ 6.2.1 of
Recommendation\ X.300).
.RT
.LP
.rs
.sp 9P
.ad r
\fBFigure 3/I.510, (N), p.\fR
.sp 1P
.RT
.ad b
.RT
.sp 1P
.LP
6.1.2
\fIInterworking using two\(hystage selection\fR \fI(two\(hystage\fR
\fIinterworking)\fR
.sp 9p
.RT
.PP
Interworking using two\(hystage selection is sometimes required,
e.g.\ access to a PSPDN through an ISDN according to case\ A of
Recommendation\ X.31. In this example, each of the terminals involved in a
communication has assigned to it a directory number from the numbering
plan of the PSPDN. For call establishment, two\(hystage selection is assumed:
first, a
connection is established through the ISDN to the appropriate PSPDN port;
second, a connection is established through the PSPDN to the called
terminal.
.PP
The logical appearance of interworking by two\(hystage selection at
reference point\ K\d2\u(see Note\ 1) may be that of a customer access (see
Figure\ 4/I.510).
.PP
The application of existing interfaces and the specification of
new interfaces at the K\d2\u\ reference point for interworking by two\(hystage
selection is for further study.
.PP
\fINote\ 1\fR \ \(em\ Since, in the case of interworking using two\(hystage
selection depicted in Figure\ 4/I.510, no IWFs are required in the ISDN, only
reference point\ K\d2\uis relevant.
.PP
\fINote\ 2\fR \ \(em\ In Recommendation X.300, examples of this category of
interworking are defined as \*Qinterworking by port access\*U (see \(sc\
6.2.2 of
Recommendation\ X.300).
.bp
.RT
.LP
.rs
.sp 9P
.ad r
\fBFigure 4/I.510, (N), p.\fR
.sp 1P
.RT
.ad b
.RT
.sp 2P
.LP
6.2
\fIISDN\(hyto\(hyISDN interconnection\fR
.sp 1P
.RT
.sp 1P
.LP
6.2.1
\fIReference configuration\fR
.sp 9p
.RT
.PP
With regard to ISDN\(hyto\(hyISDN interworking in the context of the
I.500\(hySeries of Recommendations, the functionality required for bearer
service interworking is contained in ISDN\(hyto\(hyISDN internetwork interfaces.
.PP
Figure\
5/I.510 shows a reference configuration for ISDN\(hyto\(hyISDN
interworking. The services offered at the endpoints may be different.
.PP
ISDN\(hyto\(hyISDN interworking may involve the functionality required
for interworking to take place between ISDNs operated by, for instance,
different Administrations.
.RT
.LP
.rs
.sp 14P
.ad r
\fBFigure 5/I.510, (N), p.\fR
.sp 1P
.RT
.ad b
.RT
.sp 1P
.LP
6.2.2
\fIConnection types\fR
.sp 9p
.RT
.PP
Applicable Recommendation: I.520.
.RT
.LP
a)
ISDN circuit mode | (hy | SDN circuit mode (both ISDNs supporting
a circuit\(hyswitched bearer service);
.LP
b)
ISDN packet mode | (hy | SDN packet mode (both ISDNs supporting
the ISDN virtual circuit bearer service defined in
Recommendation\ X.31 under case\ b);
.LP
c)
ISDN packet mode | (hy | SDN circuit mode (interworking where
a packet switched bearer is requested by one ISDN and a
circuit switched bearer by the other ISDN);
.LP
d)
ISDN packet mode | (hy | SDN circuit mode (interworking,
where a circuit switched bearer is requested in one ISDN
to obtain access to the packet handler of another ISDN for
communication over an ISDN virtual circuit bearer
service).
.bp
.sp 2P
.LP
6.3
\fIInterworking between ISDNs and other networks\fR
.sp 1P
.RT
.sp 1P
.LP
6.3.1
\fIReference configurations\fR
.sp 9p
.RT
.PP
Network interworking is required whenever an ISDN and a non\(hyISDN
are interconnected to provide an end\(hyto\(hyend connection.
.PP
Network interworking functions typically would contain the
functionality needed for conversion of physical and electrical interface
characteristics and for mapping of layer\ 2 and layer\ 3 network protocols.
Examples of such network interworking functions are: signalling conversions,
information transfer, protocol conversions, analogue\(hyto\(hydigital (and
\fIvice\fR
\fIversa\fR ) conversions, and interworking between different numbering
and charging plans.
.PP
Two reference configurations for network interworking are shown
in Figure\ 6/I.510. The services offered at the endpoints may be
different.
.PP
The separation between an ISDN and a non\(hyISDN may not always be
obvious. A local exchange may, for example, support both traditional telephony
service and ISDN services. The physical network components supporting these
services may be inseparable. From a functional perspective, such a case
might be covered by a) of Figure\ 6/I.510, while b) of Figure\ 6/I.510
might be more
appropriate from an implementation point of view.
.RT
.LP
.rs
.sp 16P
.ad r
\fBFigure 6/I.510, (N), p.\fR
.sp 1P
.RT
.ad b
.RT
.sp 2P
.LP
6.3.2
\fIConnection types\fR
.sp 1P
.RT
.sp 1P
.LP
6.3.2.1
\fIISDN\(hyPSTN\fR
.sp 9p
.RT
.PP
Applicable Recommendation: I.530.
.RT
.LP
a)
ISDN circuit mode\(hyPSTN
.LP
\(em
speech
.LP
\(em
3.1 kHz
.LP
\(em
64 kbit/s unrestricted
.LP
b)
ISDN packet mode, X.31 case b)\(hyPSTN.
.sp 1P
.LP
6.3.2.2
\fIISDN\(hyCSPDN\fR
.sp 9p
.RT
.PP
Applicable Recommendation: I.540.
.RT
.LP
a)
ISDN circuit mode\(hyCSPDN;
.LP
b)
ISDN packet mode, X.31 case b)\(hyCSPDN
.bp
.sp 1P
.LP
6.3.2.3
\fIISDN\(hyPSPDN\fR
.sp 9p
.RT
.PP
Applicable Recommendation: I.550.
.RT
.LP
a)
ISDN circuit mode\(hyPSPDN;
.LP
b)
ISDN circuit mode, to provide interworking port access
to a PSPDN, X.31, case\ a);
.LP
c)
ISDN packet mode, X.31 case b)\(hyPSPDN.
.sp 1P
.LP
6.3.2.4
\fIISDN\(hyTelex\fR
.sp 9p
.RT
.PP
Applicable Recommendation: I.560.
.RT
.LP
a)
ISDN circuit mode\(hyTelex
.LP
b)
ISDN packet mode\(hyTelex
.sp 1P
.LP
6.3.2.5
\fIISDN\(hyPrivate networks\fR
.sp 9p
.RT
.PP
Interworking between ISDNs and private networks may occur at
reference points S/T; other reference points, if required, need to be
specified.
.RT
.sp 1P
.LP
6.4
\fIISDN internal interworking\fR
.sp 9p
.RT
.PP
Internal ISDN interworking involves the capabilities required for interworking
between different connection elements within an ISDN, as well as the capabilities
required to support other interworking requirements within an ISDN.
.PP
A reference configuration is given in Figure\ 7/I.510. The services
offered at the endpoints may be different.
.PP
Not all aspects of internal ISDN interworking may be subject to
standardization. The existence and functionality of such interworking,
however, may have an impact on the required functionality of network interworking
or
ISDN\(hyto\(hyISDN interworking.
.RT
.LP
.rs
.sp 15P
.ad r
\fBFigure 7/I.510, (N), p.\fR
.sp 1P
.RT
.ad b
.RT
.sp 1P
.LP
6.5
\fINetwork concatenation configurations\fR
.sp 9p
.RT
.PP
\fINote\ 1\fR \ \(em\ The impact of network concatenation configurations
(i.e.\ cascaded networks) on ISDN and existing networks and on the mechanisms
and functionalities for the realization of these networks is for further
study.
.PP
\fINote\ 2\fR \ \(em\ In the case of cascaded (concatenated) networks,
other than ISDN networks, a requirement may exist for interworking functions
between pairs of such networks.
.bp
.RT
.sp 1P
.LP
6.5.1
\fIReference configurations\fR
.sp 9p
.RT
.PP
See Figure 8/I.510.
.RT
.LP
.rs
.sp 18P
.ad r
\fBFigure 8/I.510, (N), p.\fR
.sp 1P
.RT
.ad b
.RT
.sp 2P
.LP
6.5.2
\fIConnection types\fR
.sp 1P
.RT
.sp 1P
.LP
6.5.2.1
\fIISDN\(hyPSTN\(hyISDN\fR
.sp 9p
.RT
.PP
Applicable alternatives at reference points K\dx\uare described in \(sc\
6.3.2.1 and in Recommendation\ I.520.
.RT
.sp 1P
.LP
6.5.2.2
\fIISDN\(hyPSPDN\(hyISDN\fR
.sp 9p
.RT
.PP
Applicable alternatives at reference points K\dx\uare described in \(sc\
6.3.2.3 and in Recommendation\ I.520.
.RT
.sp 1P
.LP
6.5.2.3
\fIISDN\(hyCSPDN\(hyISDN\fR
.sp 9p
.RT
.PP
Applicable alternatives at reference points K\dx\uare described in \(sc\
6.3.2.2 and in Recommendation\ I.520.
.RT
.sp 1P
.LP
6.5.2.4
\fIISDN\(hyPSPDN\(hyPSTN\fR
.sp 9p
.RT
.PP
Applicable alternatives at reference points K\dx\uare described in \(sc\
6.3.2.3.
.RT
.sp 1P
.LP
6.5.2.5
\fIISDN\(hyPSPDN\(hyCSPDN\fR
.sp 9p
.RT
.PP
Applicable alternatives at reference points K\dx\uare described in \(sc\
6.3.2.3.
.RT
.sp 1P
.LP
6.5.2.6
\fIISDN\(hyPSPDN\(hyTelex\fR
.sp 9p
.RT
.PP
Applicable alternatives at reference points K\dx\uare described in \(sc\
6.3.2.3.
.RT
.sp 1P
.LP
6.5.2.7
\fIISDN\(hyCSPDN\(hyPSPDN\fR
.sp 9p
.RT
.PP
Applicable alternatives at reference points K\dx\uare described in \(sc\
6.3.2.2.
.bp
.RT
.sp 2P
.LP
\fB7\fR \fBInterworking functional requirements \(em General aspects\fR
.sp 1P
.RT
.sp 1P
.LP
7.1
\fICategories of interworking functions\fR
.sp 9p
.RT
.PP
The following network\(hyrelated characteristics and protocols depend on
the network type (ISDN circuit\(hyswitched, ISDN packet\(hyswitched, PSTN,
CSPDN, PSPDN,\ etc.) and may be identified at the point of network interworking
for
conversion or mapping:
.RT
.LP
a)
network characteristics related to the connection type,
such as interface characteristics, switching mode, bit rate,
transfer mode,\ etc., and non\(hyprotocol conversion\(hyrelated
characteristics such as numbering plan and special
routing;
.LP
b)
network\(hyto\(hynetwork protocols used for call establishment
interexchange signalling, such as SS No.\ 7, X.71, X.75,\ etc.
(e.g.\ SS No.\ 7 ISUP to another User Part of SS No.\ 7, SS No.7 to
non\(hyISDN signalling system, D\(hychannel signalling to non\(hyISDN
user access signalling systems based on national
standards);
.LP
c)
protocols used for the support of those supplementary
services and service signals which have network\(hyto\(hynetwork
relevance, as in the case, for example, of the closed user
group facility;
.LP
d)
signals due to network operation and
maintenance;
.LP
e)
inband protocol conversion IWFs such as rate adaption,
modem pools, and generation of inband tones and
announcements.
.PP
The definition of the conversion or mapping functions is
the subject of specific interworking Recommendations which address ISDN
interworking at a functional level of detail (see
Recommendation\ I.500).
.PP
Interworking functional must take into account the mapping of
protocols (protocol elements) dedicated to the support of OSI network layer
service characteristics. These requirements should be formulated with the
recognition that the networks involved in ISDN interworking may support the
OSI network layer service as defined in Recommendation\ X.213 in different
ways and to different extents (see Recommendation\ X.300,\ \(sc\ 6).
.RT
.sp 1P
.LP
7.2
\fIMapping principles\fR
.sp 9p
.RT
.PP
Interworking implies the transfer of information between two
different entities across an interface. This transfer may imply the need to
map different protocols with respect to coding, sequencing, and timing.
Ideally, no information content should be lost in mapping. This objective
may not be achievable in all circumstances. Three different cases are
identified:
.RT
.LP
a)
one\(hyto\(hyone mapping, where the information is transferred
across the interface without any loss;
.LP
b)
mapping with degraded information transfer, where parts of
information are lost when crossing the interface;
.LP
c)
no meaningful mapping possible, due to the fact that
crucial parts of one protocol cannot be represented in the
other protocol.
.PP
In these cases, appropriate actions have to be taken at the
interworking point with respect to one or both of the communicating
entities.
.sp 1P
.LP
7.3
\fIGuidelines on the description of mapping functions\fR
.sp 9p
.RT
.PP
For further study.
.RT
.sp 1P
.LP
7.4
\fIFunctional requirements for lower layer service interworking\fR
.sp 9p
.RT
.PP
(For example, mapping of layer\ 2 and layer\ 3 protocols by end
systems in support of end\(hyto\(hyend communication).
.PP
For further study.
.RT
.sp 1P
.LP
7.5
\fIFunctional requirements for higher layer service interworking\fR
.sp 9p
.RT
.PP
For further study.
.bp
.RT
.sp 2P
.LP
\fB8\fR \fBGeneral aspects of \fR \fBselection mechanisms for interworking\fR
\fBfunctions\fR
.sp 1P
.RT
.PP
ISDN interworking will involve sets of different functional
elements dedicated to the various cases of network interworking. For each
call where interworking is required, specific interworking functions have
to be
selected (see Figure\ 9/I.510).
.RT
.LP
.rs
.sp 22P
.ad r
\fBFigure 9/I.510, (N), p.\fR
.sp 1P
.RT
.ad b
.RT
.PP
When the IWF is not an addressed entity, the following concept for the
selection of interworking functions is therefore defined:
.LP
a)
Connection\(hydependent interworking functions are selected
by evaluation of user\(hynetwork and network\(hynetwork
signalling information. Relevant information includes:
.LP
\(em
bearer capability,
.LP
\(em
low layer compatibility,
.LP
\(em
service indication,
.LP
\(em
routing information (address information, transit
network information),
.LP
\(em
information on supplementary services (facilities),
if applicable;
.LP
b)
Network\(hyprovided communication\(hydependent interworking
functions are selected by evaluation of user\(hynetwork and
network\(hynetwork signalling information. Relevant information
includes:
.LP
\(em
service indication,
.LP
\(em
lower and higher layer compatibility
information,
.LP
\(em
information on supplementary services (facilities),
if applicable;
.LP
c)
End\(hysystem\(hyprovided communication\(hydependent interworking
functions, if available, are activated by one of the
following approaches:
.LP
\(em
by evaluation of user\(hynetwork signalling information
during the call establishment phase (service
indication and lower/higher compatibility
information),
.LP
\(em
by evaluation of user\(hyto\(hyuser compatibility
information during the parameter exchange
phase.
.PP
\fINote\fR \ \(em\ Examination of these information elements requires
further study.
.bp
.sp 2P
.LP
\fBRecommendation\ I.511\fR
.RT
.sp 2P
.sp 1P
.ce 1000
\fBISDN\(hyTO\(hyISDN\ LAYER\ 1\ INTERNETWORK\ INTERFACE\fR
.EF '% Fascicle\ III.9\ \(em\ Rec.\ I.511''
.OF '''Fascicle\ III.9\ \(em\ Rec.\ I.511 %'
.ce 0
.sp 1P
.ce 1000
\fI(Melbourne, 1988)\fR
.sp 9p
.RT
.ce 0
.sp 1P
.LP
\fB1\fR \fBGeneral\fR
.sp 1P
.RT
.PP
The objective of this Recommendation is to define the layer 1
aspects of the ISDN interworking, including reference configuration and
interworking functions.
.PP
\fINote\fR \ \(em\ For the international interworking between networks
based on different digital hierarchies and speech encoding laws, see
Recommendation\ G.802.
.RT
.sp 2P
.LP
\fB2\fR \fBReference configuration\fR
.sp 1P
.RT
.PP
General reference configuration and logically defined reference
points for ISDN interworking with other networks or other\ ISDNs are given in
Figure\ 4/I.310, where\ K, M and\ N are defined as logical reference points
for interworking. However, from the viewpoint of physical interworking, the
digital sections and digital links defined in Rec.\ G.701 are shared among
the logically different networks of the same network provider. Therefore,
the
commonly designated reference point for layer\ 1 interworking should be
established so that it can be used as the common layer\ 1 specification
for the logically different reference points\ K, M and\ N.
.RT
.sp 1P
.LP
2.1
\fILayer 1 reference configuration\fR
.sp 9p
.RT
.PP
Figure 1/I.511 shows the layer 1 reference configuration and
layer\ 1 reference point\ Q.
.PP
Figure 1/I.511 reflects the interworking between different network
providers each of which has logically different networks or special facilities.
The number of logically different networks which a network provider has
is one or more; however, at least one network provider should contain
an\ ISDN.
.PP
The internetwork termination\ (IT) is a functional grouping
associated with the proper physical and electromagnetic termination of the
network as well as section, link and/or circuit termination of the network.
Note that specific functions of IT may be performed with one or more pieces
of equipment.
.PP
Reference point Q should be one of the equipment interfaces listed
in Recs.\ G.702 and\ G.707. The specification of\ Q can be used as the common
description of the layer\ 1 specification for the different logical
interfaces\ K, M and\ N.
.PP
The digital link of each network should be terminated at\ Q.
.RT
.sp 1P
.LP
2.2
\fIPhysical realizations of reference configuration\fR
.sp 9p
.RT
.PP
Figure 2/I.511 gives examples of configurations made up of
combinations of physical interfaces at reference point\ Q; Figure\ 2a/I.511
shows an interface without transmission section (line or radio); and
Figures\ 2b/I.511 and\ 2c/I.511 show interfaces with transmission
sections.
.PP
In every case,
reference point\ Q
should appear as the
equipment interface.
.PP
The mandatory functions of IT described in \(sc\ 3 are the same in each
application, while the optional functions may be different according to the
following cases, if interworking:
.RT
.LP
\(em
with or without transmission sections,
.LP
\(em
with or without master\(hyslave relation, such as master\(hyslave
synchronization and remote maintenance between two network
providers.
.sp 2P
.LP
\fB3\fR \fBLayer 1 interworking functions\fR
.sp 1P
.RT
.PP
Layer\ 1 interworking functions at Q, which may be performed
by the IT, should be classified into mandatory and optional
functions.
.bp
.RT
.LP
.rs
.sp 47P
.ad r
\fBFigure 1/I.511, (N), p. 11\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.LP
.rs
.sp 47P
.ad r
\fBFigure 2/I.511, (N), p. 12\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.sp 1P
.LP
3.1
\fIMandatory functions\fR
.sp 9p
.RT
.PP
Every item related to mandatory functions should always
be carried out in order be classified into mandatory and optional
functions.
.RT
.sp 1P
.LP
3.1.1
\fIProviding standardized equipment interfaces\fR
.sp 9p
.RT
.PP
Reference point Q should be applied to one of the equipment
interfaces standardized in the G.700\(hyG.900\ Series Recommendations for
digital networks, transmission systems and multiplexing equipment.
.PP
Items to be standardized are as follows:
.RT
.LP
1)
\fIInterface bit rate\fR
.LP
Interface bit rate at Q should be selected from among the
hierarchical bit rates defined in Recs.\ G.702
and\ G.707.
.LP
It should be noted that the interworking hierarchy be
applied to the international interworking as defined in
Rec.\ G.802 when interconnection based on an asynchronous
hierarchy is adopted.
.LP
2)
\fIPhysical/electrical characteristics\fR
.LP
Physical/electrical characteristics at Q should conform to
the relevant part of G.700\(hyG.900\ Series
Recommendations.
.LP
3)
\fIFunctional characteristics\fR
.LP
Functional characteristics at Q should conform to the
relevant part of G.700\(hyG.900\ Series
Recommendations.
.LP
4)
\fITime slot assignment\fR
.LP
There are two methods for assigning time slots in the frame
structure to various channels: the fixed format method and
the variable format method. A set of examples of both
methods is described in Figure\ 3/I.511.
.LP
\fIFixed format\fR \ \(em\ Time slots for interworking information
channels are pre\(hyassigned in a fixed manner in the
interworking frame structure by bilateral
negotiation.
.LP
\fIVariable format\fR \ \(em\ A flexible time slot is allocated to any
information channel on a demand assignment basis.
.LP
5)
\fITime slot sequence integrity\fR
.LP
Time slot sequence integrity should be performed.
Furthermore, it is preferable to perform time slot sequence
integrity with 8\ kHz integrity.
.LP
\fI\fR .rs
.sp 20P
.ad r
\fBFigure 3/I.511, (N), p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.sp 1P
.LP
3.1.2
\fIProviding layer 1 maintenance capability\fR
.sp 9p
.RT
.PP
Reference point Q should meet the maintenance requirements defined in the
relevant part of the M\(hySeries and N\(hySeries Recommendations.
.PP
Items to be standardized are as follows:
.RT
.LP
1)
\fITermination of the digital link\fR
.LP
Termination of the digital link should conform
to the relevant part of the M\(hySeries
Recommendations.
.LP
2)
\fITermination of the digital circuit\fR
.LP
Termination of the digital circuit should conform
to the relevant part of the M\(hySeries Recommendations and is
deferred for further study.
.sp 1P
.LP
3.2
\fIOptional functions\fR
.sp 9p
.RT
.PP
Not all of the items of the optional functions can be achieved at reference
point\ Q. Only some of them are selected according to the features of each
connection type or differences in the relationship between network
providers.
.RT
.sp 1P
.LP
3.2.1
\fIProviding interworking between different connection types\fR
\fIin layer\ 1\fR
.sp 9p
.RT
.PP
In some applications, connection types which are different in
layer\ 1 items can be successfully interconnected over reference point\ Q by
using the optional capabilities listed below.
.PP
Items to be standardized are as follows:
.RT
.LP
1)
\fICoding rule conversion\fR
.LP
i)
\(*m\(hyA law coding rule conversion should be performed
according to Rec.\ G.802 in the case of speech and
3.1\ kHz audio services;
.LP
ii)
Unrestricted 64\ kbit/s digital service shall not be
subject to network provided conversion.
.LP
2)
\fIInterconnection among connection types with different\fR \fIlayer\
1 attributes\fR
.LP
Rate adaption should be performed according to
Recs.\ I.460, I.461, I.462, I.463
and\ I.464.
.sp 1P
.LP
3.2.2
\fIProviding network synchronization clock\fR
.sp 9p
.RT
.PP
If network synchronization is performed over reference point Q by other
methods than the plesiochronous method, the clock should meet the
requirement defined in Rec.\ G.812.
.RT
.sp 2P
.LP
\fBRecommendation\ I.515\fR
.RT
.sp 2P
.sp 1P
.ce 1000
\fBPARAMETER\ EXCHANGE\ FOR\ ISDN\ INTERWORKING\fR
.EF '% Fascicle\ III.9\ \(em\ Rec.\ I.515''
.OF '''Fascicle\ III.9\ \(em\ Rec.\ I.515 %'
.ce 0
.sp 1P
.ce 1000
\fI(Melbourne, 1988)\fR
.sp 9p
.RT
.ce 0
.sp 1P
.LP
\fB1\fR \fBGeneral\fR
.sp 1P
.RT
.sp 1P
.LP
1.1
\fIScope\fR
.sp 9p
.RT
.PP
The objective of this Recommendation is to provide overall
parameter exchange principles and functional descriptions for ISDN
interworking. This Recommendation describes the principles for parameter
exchange mechanisms. It is recognized that depending on the available
(end\(hyto\(hyend) signalling capability, the exchange of parameters may
use either out\(hy or in\(hyband procedures.
.PP
Parameter exchange may be necessary to establish compatible
interworking functions for a variety of applications. Typical examples where
parameter exchange takes place include, terminal adaption compatibility
establishment, modem type selection and voice encoding compatibility
establishment. This does not imply, however, any requirement for an ISDN to
support network based modem interworking.
.bp
.PP
Figure 1/I.515 illustrates several voice and data applications,
supported by different networks and mechanisms. Parameter exchange may be
necessary where interworking between different terminals or networks (as per
other Recommendations) is required.
.PP
\fINote\fR \ \(em\ Where interworking procedures exist, the appropriate
references are made herein.
.RT
.LP
.rs
.sp 47P
.ad r
\fBFigure 1/I.515, (N), p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.sp 1P
.LP
1.2
\fIDefinitions and abbreviations\fR
.sp 9p
.RT
.PP
Use is made of the following terms within this Recommendation.
These terms do not necessarily refer to any existing protocol structure,
rather they define information requirements in the context of this
Recommendation.
.RT
.LP
\(em
\fBbearer capability information\fR
.LP
Specific information defining the lower layer
characteristics of the network.
.LP
\(em
\fBlow layer compatibility information\fR
.LP
Information defining the lower layer characteristics of a
TE or TA.
.LP
\(em
\fBhigh layer compatibility information\fR
.LP
Information defining the higher layer characteristics of a
terminal.
.LP
\(em
\fBprotocol identifier\fR
.LP
Information defining the specific protocols used by a
terminal to support data transfer.
.LP
\(em
\fBprogress indicator\fR
.LP
Information supplied to indicate to the ISDN terminal that
interworking has occurred.
.LP
\(em
\fBout\(hyband parameter exchange\fR
.LP
Information exchanged via signalling channels which are not
within the channel used for user information
transfer.
.LP
\(em
\fBin\(hyband parameter exchange\fR
.LP
Information exchanged using the same information channel as
that used for the user information transfer.
.sp 2P
.LP
\fB2\fR \fBPrinciples\fR
.sp 1P
.RT
.sp 1P
.LP
2.1
\fITypes of parameter exchanges\fR
.sp 9p
.RT
.PP
Three types of parameter exchange need to be
considered:
.RT
.LP
i)
end\(hyto\(hyend, out\(hyband as shown in Figure\ 2/I.515. Parameter
exchange is accomplished via the D\(hychannel and Signalling
Systems\ No.\ 7;
.LP
ii)
end\(hyto\(hyend, in\(hyband as shown in Figure\ 3/I.515.
.LP
iii)
Parameter exchange to select IWFs as shown in
Figure\ 4/I.515.
.PP
The in\(hyband parameter exchange occurs after the establishment of an
end\(hyto\(hyend connection and may provide for establishment of compatibility
between the endpoints, based on characteristics such as protocol, rate
adaption scheme and modem type.
.sp 1P
.LP
2.2
\fIRelationship of\fR
\fIparameter exchange\fR \fIto\fR
\fIcall\fR
\fIestablishment\fR
.sp 9p
.RT
.PP
Parameter exchange may occur:
.RT
.LP
i)
prior to call establishment (call negotiation). In this
case parameter exchange will occur using out\(hyband
techniques;
.LP
ii)
after call establishment, prior to information transfer.
In this case parameter exchange may occur using either
in\(hyband or out\(hyband techniques;
.LP
iii)
during the information transfer phase of the call. In this
case parameter exchange will occur using either in\(hyband or
out\(hyband techniques.
.sp 1P
.LP
2.2.1
\fIParameter exchange prior to call establishment (call\fR
\fInegotiation)\fR
.sp 9p
.RT
.PP
Call negotiation
may be used to satisfy a number of basic call requirements in ISDN. In
addition, call negotiation may be necessary for interworking as described
in\ I.510 (between terminals, services and networks) for:
.RT
.LP
a)
terminal section (see Recs.\ I.333, Q.931, Q.932);
.LP
b)
selection of interworking requirements when interworking
between ISDN and other dedicated networks is identified
(e.g. modem type);
.LP
c)
the appropriate selection of network (ISDN or other
network) functions to support the service required
(e.g. use of call progress indicator);
.LP
d)
the selection of network functions when interworking between
incompatible terminals is identified or when interworking of
different services is required.
.PP
Each of the requirements a) through d) above are necessary during the call
establishment phase. Therefore, call or service negotiation mechanisms
should be included within basic call establishment procedures. Further
study is required.
.bp
.LP
.rs
.sp 9P
.ad r
\fBFigure 2/I.515, (N), p. 15\fR
.sp 1P
.RT
.ad b
.RT
.LP
.rs
.sp 21P
.ad r
\fBFigure 3/I.515, (N), p. 16\fR
.sp 1P
.RT
.ad b
.RT
.LP
.rs
.sp 9P
.ad r
\fBFigure 4/I.515, (N), p. 17\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.sp 1P
.LP
2.2.1.1
\fICall negotiation types\fR
.sp 9p
.RT
.PP
Three types of call negotiation are currently
envisaged:
.RT
.LP
\(em
user to network,
.LP
\(em
network to user,
.LP
\(em
user to user.
.PP
The relationship between user\(hyto\(hyuser call negotiation and
network\(hyto\(hyuser call negotiation required further study.
.PP
Call negotiation in each of the above cases may involve the forwarding
of parameters to the destination, may involve forwarding of parameters
on
request, or may involve forward and backward negotiation to establish
compatible terminal and network parameters.
.RT
.sp 1P
.LP
2.2.1.2
\fIInformation elements available for call negotiation\fR
.sp 9p
.RT
.PP
Three information elements are currently associated with call
negotiation (see note):
.RT
.LP
\(em
bearer capability (BC);
.LP
\(em
low layer compatibility (LLC);
.LP
\(em
high layer compatibility (HLC).
.PP
The relationship of these information elements to parameter
exchange functions is for further study.
.PP
\fINote\fR \ \(em\ BC, LLC, HLC are information elements defined in
Recommendation\ Q.931.
.RT
.sp 1P
.LP
2.2.1.3
\fITransfer of information\fR
.sp 9p
.RT
.PP
The transfer of information associated with call negotiation is
illustrated in figure\ 5/I.515.
.RT
.LP
.rs
.sp 30P
.ad r
\fBFigure 5/I.515, (N), p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.sp 1P
.LP
2.2.2
\fIParameter exchange after call establishment and prior to\fR
\fIinformation transfer phase\fR
.sp 9p
.RT
.PP
This parameter exchange may be necessary when signalling to allow adequate
compatibility checking during the call set\(hyup phase is not available,
or when additional capability checking is required due to characteristics
of
the terminals which are not defined in call establishment procedures.
.PP
When out\(hyband parameter exchange is used refer to
\(sc\ 3.1.2.
.PP
When in\(hyband paramaeter exchange is used refer to
\(sc\ 3.2.1.
.RT
.sp 1P
.LP
2.2.3
\fIParameter exchange during information transfer phase\fR
.sp 9p
.RT
.PP
This parameter exchange may be necessary when configurations change during
the information transfer phase (e.g. maintenance, sub\(hychannel
information). Detailed aspects are for further study.
.RT
.LP
\fB3\fR \fBParameter exchange procedures\fR
.sp 1P
.RT
.sp 2P
.LP
3.1
\fIOut\(hyband parameter exchange\fR
.sp 1P
.RT
.sp 1P
.LP
3.1.1
\fIPrior to call establishment\fR
.sp 9p
.RT
.PP
Refer to Recs.\ Q.931 and Q.\ 764. Other protocols are for further
study.
.RT
.sp 1P
.LP
3.1.2
\fIAfter call establishment and prior to information transfer phase\fR
.sp 9p
.RT
.PP
Refer to Recs.\ Q.931 and\ Q.764.
.RT
.sp 1P
.LP
3.1.3
\fIDuring information transfer phase\fR
.sp 9p
.RT
.PP
Refer to Recs.\ Q.931 and\ Q.764.
.RT
.sp 2P
.LP
3.2
\fIIn\(hyband parameter exchange\fR
.sp 1P
.RT
.sp 1P
.LP
3.2.1
\fIAfter call establishment and prior to information transfer\fR
.sp 9p
.RT
.PP
The following parameter exchange sequence identifies one method of establishment
compatibility during interworking between an ISDN and existing
networks and between ISDNs:
.RT
.LP
\(em
call establishment phase (e.g. refer to Recs.\ Q.931
and\ Q.764);
.LP
\(em
originating terminal changes from idle condition to busy
condition;
.LP
\(em
connection enters paramters exchange phase;
.LP
\(em
connection enters information transfer
phase.
.sp 1P
.LP
3.2.1.1
\fIVoice services\fR
.sp 9p
.RT
.PP
Refers to Recommendation G.725.
.RT
.sp 1P
.LP
3.2.1.2
\fIParameter exchange mechanism for terminal adaption protocol\fR
\fIidentification\fR
.sp 9p
.RT
.PP
Some In\(hyband Parameter Exchange (IPE) procedures are in
existence, e.g.\ Appendix\ I of Recommendation\ V.110. Two circuit mode
terminal adaption procedures are emerging within CCITT (i.e.\ I.463/V.110
and
I.465/V.120). In many countries, the Terminal Adaptor\ (TA) desing may not be
controlled by the administration/RPOAs so that special forms of terminal
adaption may be deployed. To support multiple forms of terminal adaption
in a mixed ISDN/non\(hyISDN network, terminal adaption implementations
which support
multiple terminal adaption protocols will be required. For use with such
implementations, a method is needed for some applications to identify the
specific terminal adaption protocol to be used by the multifunctional
adaptor\ (MTA) devices. This will allow the terminal equipment (or appropriate
network component), to release the call where compatibility cannot be achieved,
or to request the network to provide an appropriate interworking function.
.bp
.PP
It should be noted that it is good practice to design data terminals, for
circuit\(hymode applications, which can automatically answer or originate
calls, automatically establish compatibility if possible and, if necessary,
to disconnect when connected to an incompatible terminal.
.PP
Though it is recognized that out\(hyband procedures are preferable where
applicable (i.e., intra\(hyISDN situations), for interworking with dedicated
networks, in\(hyband parameter exchange procedures may be required.
.PP
Alternative methods exist for distinguishing between terminal
adapttion protocols. One satisfactory method is the use of self identification
by examining the incoming bit stream. The method would be sed on the need
to
provide, in any TA or TE1, the ability to determine when it is connected
to an incompatible TE1 or TA/TE2 or, through an IWF, with an incompatible
terminal or another network. Appendix\ II describes one such procedure.
.PP
An alternative satisfactory method is to use protocol identification (PID)
procedure. Appendix\ I presents an in\(hyband parameter exchange procedure
for establishing a common terminal adaption\ (TA) protocol between
communicating\ TA devices.
.RT
.sp 1P
.LP
3.2.2
\fIDuring the information transfer phase\fR
.sp 9p
.RT
.PP
For further study.
.RT
.sp 2P
.LP
\fB4\fR \fBParameter exchange functions\fR
.sp 1P
.RT
.PP
Parameters exchanged to support interworking may be divided into
the following three categories. These parameters may be exchanged end\(hyto\(hyend
or between an endpoint and an IWF. The list of parameters presented here
are
examples; for any given instances of communication, different parameters
may be required.
.RT
.sp 1P
.LP
4.1
\fINumbering parameters\fR
.sp 9p
.RT
.LP
\(em
subscriber number;
.LP
\(em
sub\(hyaddress;
.LP
\(em
terminal selection
(see Recommendation\ I.333).
.sp 1P
.LP
4.2
\fIProtocol control parameters\fR
.sp 9p
.RT
.PP
Protocol control parameters can be used to identify the protocol
supported. An example is the terminal adaption protocol supported, such
as V.110, V.120.
.RT
.sp 1P
.LP
4.3
\fIDTE/DCE configuration parameters\fR
.sp 9p
.RT
.PP
DTE/DCE configuration parameters are used to identify specific
transmission or communication capabilities of the called DTE. The following
is a list of such configuration parameters:
.RT
.LP
\(em
modem type (e.g., V\(hySeries number)
.LP
\(em
data rate (e.g., 9.6 kbit/s, 56 kbit/s)
.LP
\(em
synchronization (e.g., synchronous or
asynchronous)
.LP
\(em
parity (odd, even or no parity)
.LP
\(em
transmission mode (e.g., half or full duplex)
.LP
\(em
number of start/stop bits (e.g., 1\ or\ 2)
.LP
\(em
terminal clock source (e.g., network provided, network
independent)
.LP
\(em
terminal interface signals (e.g., 106, 108)
.LP
\(em
sub\(hychannel information.
.sp 1P
.LP
4.4
\fIOperations and maintenance parameters\fR
.sp 9p
.RT
.PP
Operations and maintenance parameters are used to convey/monitor
the status of the DTE/DCE at the terminating points. Status monitored may
include:
.RT
.LP
\(em
terminal power (ON or OFF)
.LP
\(em
terminal presence (connected or disconnected)
.LP
\(em
terminal interface signals status (e.g., 106, 108)
.LP
\(em
terminal clock source (e.g., network provided, network
independent)
.LP
\(em
loopback status (e.g., ON or OFF)
.bp
.sp 2P
.LP
\fB5\fR \fBParameter exchange for selection of IWF\fR
.sp 1P
.RT
.PP
When an IWF is involved in a connection, parameters can be
exchanged to establish compatibility.
.PP
There are a variety of techniques that can be used to provide
compatibility of functions in an interworking environment. These can be
categorized into two types. A single stage approach in which the network
automatically inserts the IWF, and a two\(hystage approach in which the user
must provide additional information to complete the interworking
connection.
.PP
\fINote\fR \ \(em\ For examples of interworking configurations, refer to the
appropriate I.500\(hySeries Recommendations. Appendix\ III details examples of
parameter exchange for the selection of IWFs in the case of ISDN\(hyPSTN
interworking for data.
.RT
.sp 1P
.LP
5.1
\fISingle stage\fR
.sp 9p
.RT
.PP
In a single stage approach, the interworking function is handled
automatically by the network. In order to ensure compatibility of the
parameters the following techniques may be used:
.RT
.LP
i)
parameter registration (
service profile
)\ \(em\ the
DTE/DCE parameters are registered with
the ISDN;
.LP
ii)
parameter negotiation\ \(em\ parameter negotiation may be
possible between networks and end\(hyusers or between
networks or between users to determine parameter
compatibility where suitable signalling exists. The
signalling capabilities and parameters required
may vary and are for further study. For example, see
Appendix\ I of\ V.110;
.LP
iii)
default parameter
identification\ \(em\ the network
provides an interworking function with common parameters.
Any DCE must conform to the IWF common parameters;
.LP
iv)
parameter adaption
\ \(em\ the interworking function
recognizes and adapts to the end\(hyuser's parameters. For
example, for ISDN\(hyPSTN the interworking function may adapt
to the modulation standard of the modem (see
Appendix\ III).
.sp 1P
.LP
5.2
\fITwo stages\fR
.sp 9p
.RT
.PP
In the two\(hystage approach, during the first stage the user accesses
the IWF and establishes the required parameters. In the second stage of
the
call the IWF uses the parameters to complete the end\(hyto\(hyend
connection.
.RT
.sp 2P
.LP
\fB6\fR \fBReference\fR
.sp 1P
.RT
.PP
See Recommendation\ I.500.
.RT
.ce 1000
APPENDIX\ I
.ce 0
.ce 1000
(to Recommendation I.515)
.sp 9p
.RT
.ce 0
.ce 1000
\fBProtocol for identification of terminal adaption protocols\fR
.sp 1P
.RT
.ce 0
.PP
I.1
As shown in Figure I\(hy1/I.515 the total in\(hyband parameter exchange
consists of two distinct phases. These are:
.sp 1P
.RT
.LP
a)
Phase\ 1\ \(em
the protocol identification (PID) phase,
which occurs at the bearer rate (64\ kbit/s);
.LP
b)
Phase\ 2\ \(em
the in\(hyband parameter exchange (IPE) which
is part of the rate adaption (RA) protocol used
during the call.
.PP
Both these phases are optional and may or may not be implemented depending
on the particular situation.
.LP
1)
Phase\ 1\ \(em
PID: after call establishment PID phase
begins.
.LP
2)
Phase\ 2\ \(em
IPE: the IPE is imbedded within the TA
protocol. It is the responsibility of the RA
protocol designers to create an IPE that is
applicable to the services and requirements of a
particular TA protocol. An example is Appendix\ I to
Rec.\ V.110 in which a complete IPE is specified
for\ V.110.
.LP
\(em
The IPE allows parameters to be exchanged between TA
devices to ensure end\(hyto\(hyend compatibility before
entering the data (information) phase.
.LP
\(em
In the case of a successful IPE the protocol enters the
data (information) phase.
.LP
\(em
In the case of unresolvable differences between the TA
devices, the IPE will provide a call progress message
that can be used to take further action or clear the
call.
.bp
.LP
.rs
.sp 40P
.ad r
\fBFigure I\(hy1/I.515, (N), p.\fR
.sp 1P
.RT
.ad b
.RT
.sp 1P
.LP
I.2
\fIIdentification procedure\fR
.sp 9p
.RT
.PP
All TA devices that follow this procedure shall start with the
simple protocol identification technique described here before entering
the TA protocol phase. The method is designed especially for digital
networks.
.PP
The
protocol identification
is performed during the following three steps after the call is placed
by using the normal call establishment
procedures:
.RT
.LP
1)
end\(hyto\(hyend synchronization;
.LP
2)
passing the Protocol Identifier (PI);
.LP
3)
making a decision regarding the type of TA to use for the
call.
.bp
.PP
For the case of a device with a PID and one without a PID which
interwork, a timer value (\fIN\fR\d\fIp\fR\\d\fIi\fR\\d\fId\fR\u) should
be set in the PID for defaulting to the preferred terminal adaption protocol.
\fIN\fR\d\fIp\fR\\d\fIi\fR\\d\fId\fR\umust be long enough to allow for
initial line settling and short enough to prevent the PID from causing
the terminal adaption protocol to time out and clear its call. The value
of timer \fIN\fR\d\fIp\fR\\d\fIi\fR\\d\fId\fR\ushould be set to allow for
long delay
connections (e.g. satellites).
.PP
Refer to Figure\ I\(hy2/I.515 for the timer sequence diagram of a
successful protocol identification procedure. The sequence and acronyms in
Figure\ I\(hy2/I.515 are described in \(sc\(sc\ I.3 to\ I.5.
.RT
.LP
.rs
.sp 45P
.ad r
\fBFigure I\(hy2/I.515, (N), p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.sp 1P
.LP
I.3
\fIEnd\(hyto\(hyend synchronization\fR
.sp 9p
.RT
.PP
After the physical call has been established, the originating end sends
continuous ready bytes (5Fhex) waiting to detect the answering
end. The answering end sends continuous sync bytes (57hex). (See
Figure\ I\(hy3/I.515).
.PP
When the originating end sees at least 32 contiguous sync bytes
(57hex) it is in sync and starts sending continuous sync bytes (57hex).
.PP
When the answering end sees 32 contiguous sync bytes it is in
sync.
.PP
The receivers at each end wait for at least 32 contiguous
occurrences (4\ ms) of the sync byte to be received without corruption before
initiating the protocol. The sequence can then proceed to the next
step.
.PP
The synchronization method described in this section allows
for:
.RT
.LP
1)
settling of the physical circuit;
.LP
2)
notice in the network;
.LP
3)
positive identification of the fact that TA devices are
present at both ends;
.LP
4)
transmission on restricted 64 kbit/s links and through
networks that use bit\ 8 for signalling; and
.LP
5)
simple implementation.
.ce
\fBH.T. [T1.515]\fR
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
lw(36p) | cw(18p) sw(18p) sw(18p) sw(18p) sw(18p) sw(18p) sw(18p) sw(18p) sw(36p) , ^ | c | c | c | c | c | c | c | c | l.
Initialization bytes
B1 B2 B3 B4 B5 B6 B7 B8
_
.T&
lw(36p) | cw(18p) | cw(18p) | cw(18p) | cw(18p) | cw(18p) | cw(18p) | cw(18p) | cw(18p) | cw(36p) .
Originating end 0 1 0 1 1 1 1 1 (5F in hexadecimal)
_
.T&
lw(36p) | cw(18p) | cw(18p) | cw(18p) | cw(18p) | cw(18p) | cw(18p) | cw(18p) | cw(18p) | cw(36p) .
Answering end 0 1 0 1 0 1 1 1 {
(57 in
hexadecimal)
}
.TE
.LP
\fINote\ 1\fR
\ \(em\ B1 is transmitted and received first.
.LP
\fINote\ 2\fR
\ \(em\ B8 is set to 1 for transmission and ignored
on reception.
.LP
FIGURE\ I\(hy3/I.515
.nr PS 9
.RT
.ad r
\fBFigure I\(hy3/I.515 (comme tableau) [T1.515], p.\fR
.sp 1P
.RT
.ad b
.RT
.sp 1P
.LP
I.4
\fIPassing the protocol identifier\fR \fI(PI)\fR
.sp 9p
.RT
.PP
This is the critical information that is to be passed and therefore a special
technique is used to provide robustness in the face of noise, and yet maintain
simplicity.
.PP
The PI is split into two bytes and three identical pairs are sent
(refer to Figure\ I\(hy4/I.515).
.RT
.PP
The PI passing technique described in this section:
.LP
1)
provides positive identification of the protocol bytes
(low and high byte codes);
.LP
2)
provides redundant pairs of byte codes which allows for a
technique to determine the protocol identification in the
presence of noise (i.e. repeated three times);
.LP
3)
allows all eight bits of the PI to be used even on networks
that use bit\ 8 for signalling; and
.LP
4)
allows for operation on restricted 64\ kbit/s networks and
networks that use bit\ 8 for signalling (i.e. guarantees
one's density, bit\ 8 set to\ 1).
.sp 1P
.LP
I.5
\fITA decision\fR
.sp 9p
.RT
.PP
After the answering end has received 32 contiguous sync\(hybytes
(\(sc\ I.3), it then sends its PI. The protocols supported by the answering
end are coded in the PI byte (see Figure\ I\(hy5/I.515) and transmitted
to the originating end. The originating end will check the PI and decide
which (if any) TA
protocol it wishes to support.
.bp
.RT
.LP
.rs
.sp 19P
.ad r
\fBFigure I\(hy4/I.515, (N), p. 22\fR
.sp 1P
.RT
.ad b
.RT
.ce
\fBH.T. [T2.515]\fR
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(24p) | cw(24p) | cw(24p) | cw(24p) | cw(24p) | cw(24p) | cw(24p) | cw(24p) .
P7 P6 P5 P4 P3 P2 P1 P0
_
.T&
cw(24p) | cw(24p) | cw(24p) | cw(24p) | cw(24p) | cw(24p) | cw(24p) | cw(24p) .
V.110 V.120 X.30 X.31 res. res. res. res. | ua\d\u)\d
.TE
.LP
Example:\ 11000000 supports V.110 and V.120 protocols.
.LP
\fINote\fR
\ \(em\ Bits marked \*Qres.\*U are set to 0, pending
future allocation.
.LP
\ua\d\u)\d\ Use of P0 as an extension bit is for further
study.
.LP
FIGURE\ I\(hy5/I.515
\fBPI interpretation\fR
.nr PS 9
.RT
.ad r
\fBFigure I\(hy5/I.515 (comme tableau) [T2.515], p. 23\fR
.sp 1P
.RT
.ad b
.RT
.PP
After the answering end has sent its PI, it sends a distinct \*Qidle byte\*U
(see Figure\ I\(hy6/I.515) continuous and waits for the matching PI from
the originating end.
.ce
\fBH.T. [T3.515]\fR
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(18p) | cw(18p) | cw(18p) | cw(18p) | cw(18p) | cw(18p) | cw(18p) | cw(18p) | lw(48p) .
B1 B2 B3 B4 B5 B6 B7 B8
_
.T&
cw(18p) | cw(18p) | cw(18p) | cw(18p) | cw(18p) | cw(18p) | cw(18p) | cw(18p) | cw(48p) .
0 1 1 1 1 1 1 1 (7F in hexadecimal)
.TE
.LP
\fINote\ 1\fR
\ \(em\ B1 is transmitted and received first.
.LP
\fINote\ 2\fR
\ \(em\ B8 is set to 1 for transmission and ignored
on reception.
.LP
FIGURE I\(hy6/I.515
\fBIdle byte\fR
.nr PS 9
.RT
.ad r
\fBFigure I\(hy6/I.515 (comme tableau) [T3.515], p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.PP
The originating end then sends back its PI with only the bit that corresponds
to the desired TA protocol set to\ 1.
.PP
If the originating end cannot support any of the answering end's TA
protocols, it sends back a null PI byte (Figure\ I\(hy7/I.515), and then
terminates the call using normal call disconnection procedures.
.RT
.ce
\fBH.T. [T4.515]\fR
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(18p) | cw(18p) | cw(18p) | cw(18p) | cw(18p) | cw(18p) | cw(18p) | cw(18p) | lw(48p) .
P0 P1 P2 P3 P4 P5 P6 P7
_
.T&
cw(18p) | cw(18p) | cw(18p) | cw(18p) | cw(18p) | cw(18p) | cw(18p) | cw(18p) | cw(48p) .
0 0 0 0 0 0 0 0 {
(00 in hexadecimal)
FIGURE\ I\(hy7/I.515
\fBNull PI byte\fR
}
_
.TE
.nr PS 9
.RT
.ad r
\fBFigure I\(hy7/I.515 (comme tableau) [T4.515], p.\fR
.sp 1P
.RT
.ad b
.RT
.PP
The method described in this section:
.LP
a)
supports various CCITT recognized forms of TA
schemes;
.LP
b)
allows for future TA schemes;
.LP
c)
limits the proliferation of TA schemes;
.LP
d)
allows the originating end to control the selection of the
common TA protocol; and
.LP
e)
provides a positive indication of a failed
call.
.ce 1000
APPENDIX\ II
.ce 0
.ce 1000
(to Recommendation I.515)
.sp 9p
.RT
.ce 0
.ce 1000
\fBTA protocol self identification\fR
.sp 1P
.RT
.ce 0
.PP
This appendix discusses guidelines for self\(hyidentification
procedures that may be used by multi\(hyprotocol terminal adaptor (MTA)
implementations in selecting the protocol to be used on an individual
connection. It is assumed that the multi\(hyprotocol terminal adaptor supports
the procedures of Recs.\ I.463 (V.110) and I.465\ (V.120). Where out\(hyband
signalling is available, multi\(hyprotocol terminal adaptors should function
in accordance
with the protocol negotiated during call set\(hyup. Self\(hyidentification
procedures are only applicable where such signalling capabilities are not
available.
.sp 1P
.RT
.sp 1P
.LP
II.1
\fIMTAs intended to interwork with uni\(hyprotocol TAs\fR
.sp 9p
.RT
.PP
The MTA may initiate transmission as if it were a uni\(hyprotocol TA conforming
to any of the capabilities provided. The received signals would be examined
by the MTA and the MTA should revert to transmission in accordance
with the procedures of the protocol of the uni\(hyprotocol TA as indicated
by the received signals. If compatibility is not achieved it would provide
a
disconnect.
.PP
It is noted that there is a range of capabilities that may be
implemented in TAs conforming to either Rec.\ I.463 (V.110) or Rec.\ I.465
(V.120). For distinguishing the capabilities of the different TA protocols,
an MTA should follow the procedures specified in the individual
Recommendations.
.RT
.sp 1P
.LP
II.2
\fIMTAs intended to interwork with other MTAs\fR
.sp 9p
.RT
.PP
The MTA should initiate transmission, following the connect
indication, in accordance with Rec.\ I.465\ (V.120).
.PP
\fINote\fR \ \(em\ Self identification can be extended to accommodate multiple
protocols. It is only necessry to define the priority for the use of each
protocol and a retry procedure. The general rule would be that an MTA would
always initiate transmission assuming the protocol of the highest priority
suported that has not been tried. The MTA would always delay disconnect,
when the received signal is not recognized, for a period long enough for
the
necessary number of retries [this is protocol and implementation
dependent\ \(em\ see, for example, Recs.\ I.463 (V.110) and
I.465\ (V.120)].
.bp
.RT
.ce 1000
APPENDIX\ III
.ce 0
.ce 1000
(to Recommendation I.515)
.sp 9p
.RT
.ce 0
.ce 1000
\fBParameter exchange for selection of IWFs\fR
.sp 1P
.RT
.ce 0
.ce 1000
\fBin the case of ISDN\(hyPSTN data interworking\fR
.ce 0
.LP
III.1
\fIMechanisms for modem selection\ \(em\ General options\fR
.sp 1P
.RT
.PP
The IWF would have to cooperate with the user to establish the
appropriate modem selection. The interworking function may also be required
to convert the signalling format, and negotiate the required data signalling
rate (modem rate).
.PP
There are two general categories of modem selection
techniques:
.RT
.LP
a)
mechanisms which do not require the ISDN user to have prior\fR knowledge
of the modem characteristics of the PSTN
user;
.LP
b)
mechanisms which may require the ISDN user to have prior\fR knowledge
of the modem characteristics of the PSTN
user.
.PP
\fINote\fR \ \(em\ The preferred methods for modem selection for ISDN\(hyPSTN
calls are for further study.
.sp 2P
.LP
III.1.1
\fIMechanisms which do not require the ISDN user to have prior\fR \fIknowledge
of the modem characteristics of the PSTN user\fR
.sp 1P
.RT
.sp 1P
.LP
III.1.1.1
\fIUse of a multi\(hystandard modem at the IWF\fR
.sp 9p
.RT
.PP
The modem in the IWF recognizes and adapts to the end\(hyuser
modulation standard. The number of, and choices of, modulation standards
that would be supported in the IWF is for further study and would normally
be a
service provider option. For examples of possible implementation see
Recs.\ V.100 and\ V.32.
.RT
.sp 1P
.LP
III.1.1.2
\fINegotiation\fR
.sp 9p
.RT
.PP
Negotiation between end\(hyuser and network or between networks or
between users to determine compatible modem characteristics may be possible
where suitable signalling methods exist. The signalling capabilities and
parameters required are for further study, and would normally be a service
provider option.
.RT
.sp 1P
.LP
III.1.1.3
\fIRegistration\fR
.sp 9p
.RT
.PP
The DTE/DCE characteristics of the PSTN user are registered with
the ISDN.
.RT
.sp 2P
.LP
III.1.2
\fIMechanisms which may require the ISDN user to have prior\fR
\fIknowledge of modem characteristics of the PSTN user\fR
.sp 1P
.RT
.sp 1P
.LP
III.1.2.1
\fIDefault identification\fR
.sp 9p
.RT
.PP
Any DTE uses the same default modem characteristics.
.RT
.sp 1P
.LP
III.1.2.2
\fISelection by ISDN user of the modem dynamically\fR
.sp 9p
.RT
.PP
Using available parameter exchange mechanisms (i.e. SN,
LLC/BC, IPE) the user selects specific TA/modem characteristics at
the\ IWF.
.RT
.sp 2P
.LP
III.2
\fIISDN bearer capabilities for interworking\fR
.sp 1P
.RT
.sp 1P
.LP
III.2.1
\fI3.1 kHz ISDN bearer capability\fR
.sp 9p
.RT
.PP
See Figure III\(hy1/I.515.
.PP
In the scenario the following cases are considered:
.RT
.LP
\(em
terminal is connected to ISDN access via a modem and uses a
3.1\ kHz audio bearer through TA;
.LP
\(em
terminal selection in ISDN is made by means of multiple
subscribers numbers.
.bp
.PP
The PSTN user uses only the number corresponding to the
appropriate terminal in ISDN for a call to that terminal. ISDN user does the
same for calls to other terminals in ISDN or PSTN.
.LP
.rs
.sp 8P
.ad r
\fBFigure III\(hy1/I.515, (N), p.\fR
.sp 1P
.RT
.ad b
.RT
.sp 1P
.LP
III.2.2
\fI64 kbit/s ISDN bearer capability\fR
.sp 9p
.RT
.PP
The following modem selection procedures apply to ISDN\(hyPSTN
interworking (see Figure\ III\(hy2/I.515) since the ISDN and PSTN will share
network transmission and switching facilities. These modem selection procedures
assume that the modem interworking point will be the originating (for ISDN
to PSTN calls) or terminating (for PSTN to ISDN calls) ISDN exchange, i.e.
modem pools are available at each ISDN exchange.
.PP
The modems in the modem pool at each ISDN exchange can be grouped
by their speeds; suitable codes and/or full Subscriber Numbers (SNs) can
be assigned to each group of modems.
.RT
.LP
.rs
.sp 12P
.ad r
\fBFigure III\(hy2/I.515, (N), p.\fR
.sp 1P
.RT
.ad b
.RT
.sp 1P
.LP
III.3
\fIOptions for modem selection\fR
.sp 9p
.RT
.PP
The modem selection procedures outlined in this section are
provided as potential options, which Administrations may choose, with
modifications as required, to suit their own operating environment and
applications.
.RT
.sp 2P
.LP
III.3.1
\fIISDN\(hyPSTN calls (bidirectional)\fR
.sp 1P
.RT
.sp 1P
.LP
III.3.1.1
\fIOption 1 (example of the method detailed in \(sc\ III.1.1.1)\fR
.sp 9p
.RT
.PP
This is a single stage modem selection procedure which relies upon the
following system requirements:
.RT
.LP
\(em
data terminals on the ISDN have separate SNs;
.LP
\(em
the ISDN exchange can distinguish whether any incoming call
is from the PSTN and can distinguish that an outgoing call is
destined for the PSTN.
.bp
.PP
For a voice\(hyband data call originated by a PSTN terminal, and
intended for a data terminal on the ISDN, the terminating ISDN exchange will
intercept the call and direct the call to an IWF. At the IWF, a modem will
be inserted into the path, and the modem will recognize and adapt to the
modulation standard used by the PSTN user. The IWF may pass parameters
(e.g.\ LLC) to the called user when establishing the ISDN portion of
the call.
.PP
For a data call originated in the ISDN intended for a data terminal
on the PSTN, the ISDN exchange will intercept the call and direct the call
to the IWF. The IWF will use the requested service (BC/LLC) on the ISDN
portion
of the call. At the IWF, a modem will be inserted into the path, and the
modem will recognize and adapt to the modulation standard used by the
PSTN user.
.RT
.sp 1P
.LP
III.3.1.2
\fIOption 2 (example of the method detailed in III.1.1.3)\fR
.sp 9p
.RT
.PP
This is a single stage modem selection procedure which relies on
the following system requirements:
.RT
.LP
\(em
circuit data terminals on ISDN loops have
separate SNs;
.LP
\(em
a call progress indicator that PSTN to ISDN, or ISDN to PSTN
interworking has occurred; and
.LP
\(em
service profiles of destination terminals are available at
the ISDN exchange (data \fIvs\fR speech terminals, pre\(hysubscribed
modem type).
.sp 1P
.LP
III.3.1.2.1
\fIPSTN\(hyto\(hyISDN call\fR
.sp 9p
.RT
.PP
The terminating ISDN exchange recognizes that:
.RT
.LP
\(em
the call is from the PSTN (from the call progress
indicator);
.LP
\(em
the call is for a data terminal (from service profile);
and
.LP
\(em
the modem type subscribed to (from service
profile).
.PP
The terminating exchange will insert the pre\(hysubscribed modem
type from the pool.
.sp 1P
.LP
III.3.1.2.2
\fIISDN\(hyto\(hyPSTN call\fR
.sp 9p
.RT
.PP
The ISDN terminal will initiate the callas a 64\ kbit/s, rate
adapted digital data call for all calls to both ISDN and PSTN destinations.
On the receipt of the progress indicator (ISDN/PSTN interworking), the local
exchange will insert the pre\(hysubscribed modem type in the path.
.PP
If the calling ISDN terminal knows \fIa priori\fR | that the called
terminal in on a PSTN analogue loop, it may indicate in the \fIset\(hyup\fR
message
the pre\(hysubscribed modem type to be inserted.
.RT
.sp 2P
.LP
III.3.2
\fIISDN\(hyto\(hyPSTN calls\fR
.sp 1P
.RT
.sp 1P
.LP
III.3.2.1
\fIOption 3 (example of the method detailed in III.1.2.2)\fR
.sp 9p
.RT
.PP
For a data call originated by a data terminal on the ISDN, the
modem selection is done by using some appropriate information elements
in the Q.931 \fIset\(hyup\fR message. Modem selection by the calling party
is dependent upon the calling party's prior knowledge of the modulation
standard used by the
called party on the PSTN or upon the user of a multi\(hystandard modem
at the IWF. The appropriate modem is inserted in the end\(hyto\(hyend path.
.RT
.sp 2P
.LP
III.3.3
\fIPSTN\(hyto\(hyISDN calls\fR
.sp 1P
.RT
.sp 1P
.LP
III.3.3.1
\fIOption 4 (example of the method detailed in III.1.2.2 using\fR \fIsubscriber
number.)\fR
.sp 9p
.RT
.PP
This is a two\(hystage method in which the modem pools at each
exchange are grouped according to modulation standard and/or speed and each
group is assigned a full subscriber number\ (SN). The first stage selects an
appropriate modem and the second stage completes the connection to the
desired terminal through the selected modem. Separate SNs for the data
terminals on the ISDN digital loop are not needed because it is the responsibility
of the PSTN subscriber to request a modem from the pool when he needs a
data connection;
the IWF will generate the appropriate bearer capability. However, the PSTN
terminal equipment should have the capability to input a second set of
digits, i.e.\ the called number (e.g. using V.25 | fIbis\fR protocol).
.bp
.PP
Therefore for a PSTN\(hyto\(hyISDN data call, the PSTN user first dials
the address of the appropriate group of modems at the terminating exchange.
Once
this connection is established the PSTN user dials the address of the called
ISDN subscriber. This set of digits is used by the signalling conversion
functionality (part of the IWF at the terminating exchange) to set\ up the
connection from the modem to the called ISDN terminal. The exchange of call
progress tones for this case needs further study.
.RT
.sp 1P
.LP
III.3.3.2
\fIOption 5 (example of the method detailed in III.1.1.2)\fR
.sp 9p
.RT
.PP
This is a single\(hystage modem selection procedure which relies upon the
following system requirements:
.RT
.LP
\(em
circuit data terminals on ISDN loops have separate SNs;
.LP
\(em
PSTN terminals have suitable signalling capabilities to
indicate the modem speed/type in response to a request from
the terminating exchange;
.LP
\(em
the ISDN exchange can distinguish whether an incoming call is
from the PSTN or the ISDN (using call progress indicator);
and
.LP
\(em
the ISDN exchange maintains a data base on service profiles
of terminals served by the exchange (analog\ \fIvs\fR digital,
and speech\ \fIvs\fR data in case of digital
subscribers).
.PP
The user must be aware of any special operational
requirements.
.PP
For a voice\(hyband data call originated by a PSTN terminal, and intended
for a digital data terminal on the ISDN, the terminating ISDN exchange
will
recognize that:
.RT
.LP
\(em
the call is coming from the PSTN; and
.LP
\(em
the call is intended for a digital data terminal on the
ISDN.
.PP
The terminating ISDN exchange will intercept the call and send a suitable
tone/signal back to the originating PSTN subscriber. Using some
suitable signalling capability, the PSTN subscriber will indicate the code
for modem selection, which will be used by the terminating exchange to
attach a
suitable modem and complete the path to the digital data terminal.
.LP
.rs
.sp 27P
.sp 2P
.LP
\fBMONTAGE: RECOMMANDATION I.520 SUR LE RESTE DE CETTE PAGE\fR
.sp 1P
.RT
.LP
.bp