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.rs
.\" Troff code generated by TPS Convert from ITU Original Files
.\" Not Copyright ( c) 1991
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.EN
.nr LL 40.5P
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.po 4P
.rs
\v | 5i'
.LP
\v'36P'
\fBMONTAGE:\ \ \fR Fin de la Rec. I.320 en t\* | te de cette page\fR
.sp 2P
.LP
\fBRecommendation\ I.324\fR
.RT
.sp 2P
.sp 1P
.ce 1000
\fBISDN\ NETWORK\ ARCHITECTURE\fR
.EF '% Fascicle\ III.8\ \(em\ Rec.\ I.324''
.OF '''Fascicle\ III.8\ \(em\ Rec.\ I.324 %'
.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
\fIBasic philosophy\fR
.sp 9p
.RT
.PP
The objective of this Recommendation is to provide a common
understanding of the CCITT studies on the general architecture of an ISDN
from the functional point of view. The model is not intended to require
or exclude any specific implementation of an ISDN, but only to provide
a guide for the
specification of ISDN capabilities.
.bp
.RT
.sp 1P
.LP
1.2
\fIDefinitions\fR
.sp 9p
.RT
.PP
A number of terms used in this Recommendation are described in more detail
in other Recommendations. To assist the understanding of the reader, the
following particular definitions apply in this Recommendation:
.RT
.LP
1)
\fBreference configurations\fR are conceptual configurations which are
useful in identifying various possible arrangements in
an ISDN. The reference configurations are based on
association rules of functional groupings and reference points.
Detailed descriptions of reference configurations for ISDN
connection types are given in other I\(hyseries Recommendations.
For user\(hyto\(hynetwork access they are defined in
Recommendation\ I.411 and for interworking between networks they
are defined in the I.500\(hyseries of Recommendations.
.LP
2)
\fBfunctional groupings\fR are sets of functions which may
be needed in ISDN arrangements. The relationship between
generic functions and specific functions allocated to particular
entities (or functional groupings) in the ISDN are explained in
Recommendation\ I.310.
.LP
3)
\fBreference points\fR are the conceptual points at the
conjunction of two functional groupings. In a particular
example, a reference point may correspond to a physical
interface between pieces of equipment, or in other examples
there may not be any physical interface corresponding to the
reference point. Interfaces will not be defined by CCITT for an
ISDN unless the corresponding reference points have been already
specified.
.sp 2P
.LP
\fB2\fR \fBGeneral architecture of an ISDN\fR
.sp 1P
.RT
.PP
In practical ISDN implementations some of the ISDN functions will be implemented
within the same network elements, whereas other specific ISDN
functions will be dedicated to specialized network elements. Various different
ISDN implementations are likely to be realized depending on national
conditions.
.PP
A basic component of an ISDN is a network for circuit switching of
end\(hyto\(hyend 64\ kbit/s connections. In addition to this connection type,
depending on national conditions and evolution strategies, the ISDN will or
will not support other connection types, such as packet mode connection
types and \fIn\fR \ \(mu\ 64\ kbit/s circuit mode connection types, and
other broadband
connection types.
.RT
.sp 1P
.LP
2.1
\fIBasic architectural model\fR
.sp 9p
.RT
.PP
A basic architectural model of an ISDN is shown in Figure\ 1/I.324. This
shows the seven main switching and signalling functional capabilities of
an ISDN:
.RT
.LP
\(em
ISDN local Connection Related Functions (CRF), see
\(sc\ 4.2.2.1;
.LP
\(em
narrow\(hyband (64 kbit/s) circuit switching functional
entities;
.LP
\(em
narrow\(hyband (64 kbit/s) circuit non\(hyswitched functional
entities. (The identification and definition for\ 8, 16,
32\ kbit/s or non\(hyswitched functional entities is left for
further study.);
.LP
\(em
packet switching functional entities;
.LP
\(em
common channel inter\(hyexchange signalling functional entities,
for example conforming to CCITT Signalling System No.\ 7;
.LP
\(em
switched functional entities at rates greater than
64\ kbit/s;
.LP
\(em
non\(hyswitched functional entities at rates greater than
64\ kbit/s.
.PP
These components need not be provided by distinct networks, but
may be combined as appropriate for a particular implementation.
.PP
Higher layer functions (HLF) which may be implemented within (or
associated with) an ISDN may be accessed by means of any of the above\(hymentioned
functional entities. Those functional entities could be implemented totally
within an ISDN or be provided by dedicated networks or specialized service
providers. Both cases may provide the same ISDN teleservices (see
Recommendation\ I.210) from the user's point of view.
.bp
.RT
.LP
.rs
.sp 38P
.ad r
\fBFigure 1/I.324, (N), p. 1\fR
.sp 1P
.RT
.ad b
.RT
.sp 1P
.LP
2.2
\fIArchitectural components of the ISDN\fR
.sp 9p
.RT
.PP
Recommendation I.310 describes the functions of an ISDN. These
functions are by their nature static (i.e.,\ time\(hyindependent). The relative
distribution and allocation of these functions is the subject of the
architecture of the ISDN and is described in this Recommendation. The dynamic
aspects of these functions are modelled in Recommendation\ I.310 as Executive
Processes.
.PP
Therefore the key components in this architectural model are: what
functions are contained in the ISDN, where they are located, and what is the
relative topology for their distribution in the ISDN.
.RT
.sp 2P
.LP
\fB3\fR \fBAspects of the architecture of the ISDN\fR
.sp 1P
.RT
.PP
The architecture of the ISDN includes low layer capabilities and high layer
capabilities. These capabilities support services both within the ISDN
and via interworking (see \(sc\ 5) to other networks.
.bp
.RT
.sp 1P
.LP
3.1
\fILow layer capabilities\fR
.sp 9p
.RT
.PP
From the main functional capabilities of the ISDN, as shown in
Figure\ 1/I.324, four main functional capabilities require further
description.
.RT
.sp 1P
.LP
3.1.1
\fICircuit switching capabilities\fR
.sp 9p
.RT
.PP
Circuit\(hyswitched connections with information transfer rates up to 64\
kbit/s are carried by B\(hychannels at the ISDN user\(hynetwork interfaces
and
switched at 64\ kbit/s by the circuit\(hyswitching functional entities
of the ISDN. Circuit switching can also be applied to information transfer
rates greater
than 64\ kbit/s.
.PP
Signalling associated with circuit switched connections is carried by the
D\(hychannel at the ISDN user\(hynetwork interface and processed by the
local
CRF (see \(sc\ 4.2.2.1). User\(hyto\(hyuser signalling could be carried
through the
common channel signalling functional entities (in the transit connection
elements).
.PP
User bit rates of less than 64\ kbit/s are rate adapted to 64\ kbit/s,
as described in Recommendation\ I.460, before any switching can take place
in
the ISDN. Multiple information streams from a given user may be multiplexed
together in the same B\(hychannel, but for circuit switching an entire
B\(hychannel will be switched to a single user\(hynetwork interface. This
multiplexing should be in accordance with Recommendation\ I.460. Furthermore,
circuit switched data services with bit rates less than 64\ kbit/s (in
accordance with
Recommendation\ X.1 user classes of service) may be handled by a dedicated
circuit switched public data network to which the user gains access by
means of an ISDN connection.
.PP
The narrow\(hyband ISDN circuit switching capabilities are based on
64\ kbit/s switching. Connection types at higher bit rates could also be
provided on a semi\(hypermanent basis. Switched connections at these bit rates
could also be provided by broadband switching functional entities.
.RT
.sp 1P
.LP
3.1.2
\fIPacket switching capabilities\fR
.sp 9p
.RT
.PP
A number of packet mode bearer services are described in the
I.230\(hyseries of Recommendations. Different network solutions and corresponding
architectures may be adopted in different countries to support these services.
.PP
Recommendations I.310 (functional principles of ISDN), I.462
(definitions of minimum and maximum integration scenarios) and\ Q.513
(description of exchange connections) constitute the basis for the description
of packet switchng functions in an ISDN.
.PP
Two types of functional groupings are involved in the provision of
packet switched bearer services by an ISDN:
.RT
.LP
\(em
packet handling functional groupings
, which contain functions relating to the handling of packet calls within the
ISDN;
.LP
\(em
interworking functional groupings
, which ensure
interworking between ISDN and packet switched data
networks.
.PP
The solutions which could be used to access packet bearer services are:
.LP
\(em
via the B\(hychannel, with the following cases:
.LP
\(em
circuit (switched or semi\(hypermanent) access through
ISDN to an interworking function within a PSPDN,
.LP
\(em
circuit (switched or semi\(hypermanent) access
associated with packet handling functions and/or
interworking functions in the ISDN,
.LP
\(em
circuit (switched or semi\(hypermanent) access
associated with packet handling functions within the
ISDN;
.LP
\(em
via the D\(hychannel, with the following cases:
.LP
\(em
packet handling functions and interworking functions
within the ISDN,
.LP
\(em
packet handling functions in the ISDN (without
interworking functions).
.PP
\fINote\fR \ \(em\ This classification does not preclude a combination of
the solutions described above.
.bp
.PP
Depending on national considerations, the ISDN packet handling and
interworking functions can be centralized or distributed. The following
cases may be encountered:
.RT
.LP
\(em
packet handling and interworking functions are not
integrated in the local CRF (e.g.,\ they are located in
a transit CRF);
.LP
\(em
packet handling functions are integrated in the local CRF;
.LP
\(em
packet handling functions and/or interworking functions are
integrated in the local CRF.
.sp 1P
.LP
3.1.3
\fIOther\fR
\fIswitching capabilities\fR
.sp 9p
.RT
.PP
For the support of broadband connections, other switching
capabilities in addition to the above\(hymentioned switching capabilities
could be employed.
.RT
.sp 1P
.LP
3.1.4
\fITransmission capabilities\fR
.sp 9p
.RT
.PP
In addition to the normal transmission capabilities of the IDN
(Integrated digital network) the following transmission aspects are important
when considering the architecture of the ISDN. Services which do not require
unrestricted digital information transfer capability, such as telephony, may
also employ non\(hytransparent channels (e.g.,\ packetized voice, digital
speech
interpolation). Channels at 8, 16, 32\ kbit/s may be used in the transmission
part of the network; they may be used to support some services
(e.g.,\ voice\(hyband connection types). They may also be used in cases where a
B\(hychannel (at the S or\ T reference point) carries user data streams at bit
rates lower than\ 8, 16, 32\ kbit/s respectively.
.RT
.sp 1P
.LP
3.2
\fIHigh layer capabilities\fR
.sp 9p
.RT
.PP
Normally the high layer functions (HLFs) are involved only in the terminal
equipment, but for the support of some services, provision of HLFs
could be made via special nodes in the ISDN belonging to the public network
or to centres operated by other organizations and accessed via ISDN user\(hynetwork
or inter\(hynetwork interfaces. Some services such as message handling
service
(MHS) may be used on a large scale and the relevant functional entities
could be provided within the ISDN exchanges. For both cases the protocols
used to
activate such services should be identical and integrated with the general
user procedures defined for the activation of ISDN teleservices.
.RT
.sp 2P
.LP
\fB4\fR \fBLocation of \fR \fBfunctions in the ISDN\fR
.sp 1P
.RT
.sp 1P
.LP
4.1
\fIOverall\fR
.sp 9p
.RT
.PP
In considering an ISDN call (i.e. an instance of a
telecommunication service) two major functional areas are
involved:
.RT
.LP
i)
the customer equipment (TE and optional customer network);
.LP
ii)
the public ISDN connection type.
.PP
Recommendation I.411 describes the functional groupings and
reference configurations for the customer network, while Recommendation\
I.412 describes the channel structures to be used at reference points\
S and\ T. The
partitioning of the functions involved in\ ii), the public ISDN connection
type, is described in \(sc\ 4.2 below.
.PP
Figure\ 2/I.234 illustrates this overall division of functions involved
in a communication across the ISDN.
.RT
.sp 1P
.LP
4.2
\fIPartitioning of the \fR \fIISDN connection type\fR
.sp 9p
.RT
.PP
The distribution of functions within the ISDN connection type is
known as the
connection type reference configuration
. The partitions of the connection type to allow this distribution are
described below. The
detailed reference configurations for groups of connection types can be
found in Recommendation\ I.325.
.bp
.RT
.LP
.rs
.sp 14P
.ad r
\fBFigure 2/I.324, (N), p. 2\fR
.sp 1P
.RT
.ad b
.RT
.sp 1P
.LP
4.2.1
\fIConnection elements\fR
.sp 9p
.RT
.PP
The first level of partitioning of the ISDN connection type is the
connection element
. The partitioning is based on the two most critical transitions of a connection:
change of signalling system and the international transmission system(s).
These two points generate three connection elements:
access connection element
,
national transit connection element
, and
international transit connection element
. These three connection
elements allow the description of both the access and transit capabilities
to support services. However, in the case of performance allocation, for
example, the access connection element and the national transit connection
element may be fused into one national connection element. This allows
for the variation in the nature of the local plant and regulatory environments
in different
countries according to national policies.
.PP
The partitioning into connection elements is shown in
Figure\ 3/I.234.
.RT
.LP
.rs
.sp 15P
.ad r
\fBFigure 3/I.324, (N), p.\fR
.sp 1P
.RT
.ad b
.RT
.sp 1P
.LP
4.2.1.1
\fIAccess connection element\fR
.sp 9p
.RT
.PP
The access connection element is bounded by the T reference point at the
customer end and the reference point which marks the transition from the
access signalling system to the common channel signalling system on the
network side.
.bp
.PP
The model for the access connection element in the case of 64\ kbit/s circuit
switched is shown in Figure\ 4/I.234. Depending on the national
situations and on the type of access, a number of different possibilities
are available for this element, in particular with regard to the use of
multiplexer (MPX) or remote switching units (RSU).
.RT
.LP
.rs
.sp 17P
.ad r
\fBFigure 4/I.324, (N), p.\fR
.sp 1P
.RT
.ad b
.RT
.sp 1P
.LP
4.2.1.2
\fINational transit connection element\fR
.sp 9p
.RT
.PP
The national transit connection element is bounded by the
transition from access signalling system to common channel signalling systems
and the \fIfirst\fR | international switching centre. In the case of a
national
connection this would default to a \*Qtransit connection element\*U, i.e.\
between two local CRFs, but could involve network elements from more than
one network operator.
.PP
In some instances, the first international exchange (and the
international CRF) may be in close proximity to the local and national
transit CRF. This is a national matter.
.PP
The model for the national transit connection is shown in
Figure\ 5/I.324.
.RT
.LP
.rs
.sp 19P
.ad r
\fBFigure 5/I.324, (N), p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.sp 1P
.LP
4.2.1.3
\fIInternational connection element\fR
.sp 9p
.RT
.PP
The international connection element is bounded by the
originating and destination International Switching Centre (ISC). A number
of transit international exchanges may be involved to bridge long international
connections. With satellite connections, fewer international transits may be
required.
.PP
Figure 6/I.324 shows an international connection element model.
Figure\ 7/I.324 shows an international connection element model made by a
concatenation of several links and exchanges.
.RT
.LP
.rs
.sp 6P
.ad r
\fBFigure 6/I.324, (N), p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.rs
.sp 11P
.ad r
\fBFigure 7/I.324, (N), p.\fR
.sp 1P
.RT
.ad b
.RT
.sp 1P
.LP
4.2.1.4
\fIFuture additional connection elements\fR
.sp 9p
.RT
.PP
Connection elements for interworking and connection to specialized resources
and services are also required.
.RT
.sp 1P
.LP
4.2.2
\fIBasic connection components\fR
.sp 9p
.RT
.PP
The Basic Connection Components (BCC) allow for the analysis of system
performance. There are three forms of BCC: connection related function,
access links and transit links. Broadly, CRFs cover switching aspects,
and
links cover transmission aspects.
.RT
.sp 1P
.LP
4.2.2.1
\fIConnection related function\fR
.sp 9p
.RT
.PP
The connection related function includes all aspects involved in
establishing and controlling the connections within the particular connection
element. This includes functions such as exchange terminations, switching,
control, network management, operation and maintenance. The specific
capabilities of each CRF are not specified in the general reference model:
this is done in the reference configuration for each group of connection
types.
.RT
.sp 1P
.LP
4.2.2.2
\fIAccess link\fR
.sp 9p
.RT
.PP
The access link includes the NT1 and may include a multiplexer,
along with the required transmission equipment to link the customer network
to the local CRF.
.RT
.sp 1P
.LP
4.2.2.3
\fITransit link\fR
.sp 9p
.RT
.PP
The transit link is a digital link as described in
Recommendations\ G.701 and\ G.801.
.bp
.RT
.sp 1P
.LP
4.2.3
\fIFunctional groupings\fR
.sp 9p
.RT
.PP
Functional groupings are sets of functions which may be needed in the ISDN.
In a particular instance, specific functions in a functional group
may or may not be present. Note that specific functions in a functional
group may be performed in one or more pieces of equipment. Examples of
functional
groupings are Line Termination (LT), Exchange Termination (ET), and Packet
Handling (PH) function. Further study is required on functional groupings
for the public ISDN connection type.
.RT
.sp 1P
.LP
4.2.4
\fIReference points\fR
.sp 9p
.RT
.PP
The other element involved in the description of a reference
configuration is the reference point concept. The I\(hyseries already identifies
reference points\ S and\ T (in Recommendation\ I.411) and K, M, N, P (in
the
present Recommendation). As can be seen from Figure\ 4/I.324, some further
internal reference points need to be identified. Further study is required
to see whether these and any further reference points need to be defined.
.PP
In describing the reference configuration for the public ISDN
connection types, an important consideration vis\(hya\(hyvis the reference
points is the following. In Figure\ 3/I.324 the end points of the overall
connection is
shown as being at the T\ reference point. The reason for this is as follows.
Reference point\ S is identifical to reference point\ T when the NT2 function
is null (cf\ Recommendation\ I.411). When the NT2 function is non\(hyzero,
then the
performance of the overall connection will be made up of the performance
of the ISDN network connection (i.e.\ between the two interfaces at reference
point\ T) and the sum of the performance of the customer network connections
(i.e.\ between the interfaces at reference points\ S and\ T at each end).
Recommendation\ G.801 also uses this approach by defining the areas of the
digital hypothetical reference connection (HRX) as being at the T\ reference
point.
.RT
.sp 2P
.LP
\fB5\fR \fBArchitectural relationship between the ISDN and other networks\fR
\fBincluding ISDN\fR
.sp 1P
.RT
.PP
A key element of service integration for an ISDN is the provision of a
limited set of standard multi\(hypurpose user\(hynetwork interfaces.
.PP
It is important to note that the introduction of ISDN capabilities into
a network requires a massive development effort. Consequently, Administrations
will be introducing various ISDN functions successively over a course of
time. For example, the 64\ kbit/s circuit switched capability may be introduced
initially, followed by provision of packet switching features, and
so\ on.
.PP
An ISDN will therefore have to interwork with a set of various
dedicated networks or terminals in order to:
.RT
.LP
i)
provide ISDN connections to non\(hyISDN terminal equipments
(TE2) through dedicated networks;
.LP
ii)
provide a non\(hyISDN terminal equipment (TE2) connected by
means of a terminal adaptor (TA) with access to non\(hyISDN
services provided by a dedicated services network;
.LP
iii)
ensure that an ISDN terminal connected to ISDN
interworks with a non\(hyISDN terminal connected to a
dedicated network.
.PP
The dedicated networks will offer services (e.g.\ public data
network services) that are either available or not available within an ISDN.
Some of the dedicated networks could be integrated into the ISDN in the
future, depending on national conditions. Connections have to be allowed
between
terminals, both connected to an ISDN, or for terminals where one is connected
to the ISDN and the other is connected to the dedicated network.
.PP
The I.500\(hyseries of Recommendations describe the characteristics of
interworking.
.PP
The I.400\(hyseries of Recommendations describe the characteristics of
user\(hynetwork interfaces for the following cases:
.RT
.LP
1)
access of a single ISDN terminal;
.LP
2)
access of a multiple ISDN terminal installation;
.LP
3)
access of multiservice PABXs,
local area networks
or, more generally, private networks;
.LP
4)
access of non\(hyISDN terminal;
.LP
5)
access of specialized storage and information processing
centres.
.bp
.PP
In addition, considering that the evolution to a comprehensive
ISDN will take place over a long period of time, the connection of non\(hyISDN
customers to an ISDN via analogue lines as well as interworking with existing
networks or other ISDNs will be necessary. These cases include:
.LP
1)
access to the existing telephone network and to dedicated
networks (e.g.\ packet network, telex network);
.LP
2)
access to another ISDN;
.LP
3)
access to service providers outside the ISDN.
.PP
The ISDN user\(hynetwork interfaces or internetwork interfaces may
be used in the above cases. The definition of internetwork interfaces is
necessary for these arrangements for interworking and administrative
requirements.
.PP
Interworking with other networks or other ISDNs requires in some cases
the provision of Interworking Functions (IWF), either within the ISDN or
in
the other network (see Recommendations of the I.500\(hyseries). These functions
would ensure interworking between different protocols and user
procedures.
.PP
Within a country or geographical area, an ISDN connection may be
formed across several interconnected networks, each of which is characterized
by the attributes of one or more ISDN connection types (as defined in
Recommendation\ I.340).
.PP
Figure 8/I.324 depicts the ISDN user\(hynetwork reference points as
defined in the I.400\(hyseries of Recommendations, as well as reference
points at which internetwork interfaces between an ISDN and other networks
(including
other ISDNs) may exist. Whether internetwork interfaces at all of these
reference points will be defined by CCITT Recommendations is for further
study.
.RT
.LP
.rs
.sp 30P
.ad r
\fBFigure 8/I.324, (N), p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.PP
Examples of possible interworking situations are given in
Figures\ 9/I.324, 10/I.324 and 11/I.324.
.PP
Figure 9/I.324 shows cases where some ISDN services are also provided to
subscribers connected to dedicated networks. In these circumstances ISDNs
have to interwork with such networks.
.PP
Figure 10/I.324 primarily shows cases where a dedicated network is
used to carry a given class of ISDN services. As an example, a dedicated
packet switched network providing X.25 services to its subscribers could be
used to set up ISDN packet connections between two ISDN subscribers. From an
ISDN services perspective, this could be viewed as a subset of ISDN.
.PP
The dedicated network may be composed of dedicated transmission and
switching facilities or be restricted to a set of special nodes linked
together via connections, provided through the circuit switched part of
the ISDN
network, as illustrated in Figure\ 11/I.324, for the example of a packet
switched network.
.RT
.LP
.rs
.sp 38P
.ad r
\fBFigure 9/I.324, (N), p. 9\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.LP
.rs
.sp 25P
.ad r
\fBFigure 10/I.324, (N), p. 10\fR
.sp 1P
.RT
.ad b
.RT
.LP
.rs
.sp 23P
.ad r
\fBFigure 11/I.324, (N), p. 11\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.sp 2P
.LP
\fBRecommendation\ I.325\fR
.RT
.sp 2P
.sp 1P
.ce 1000
\fBREFERENCE\ CONFIGURATIONS\ FOR\ ISDN\ CONNECTION\ TYPES\fR
.EF '% Fascicle\ III.8\ \(em\ Rec.\ I.325''
.OF '''Fascicle\ III.8\ \(em\ Rec.\ I.325 %'
.ce 0
.sp 1P
.ce 1000
\fI(Melbourne, 1988)\fR
.sp 9p
.RT
.ce 0
.sp 1P
.LP
\fB1\fR \fBSummary\fR
.sp 1P
.RT
.PP
In order to apply the network performance parameters to the ISDN, some
form of hypothetical reference connections (HRXs) are necessary. These
HRXs should be based on appropriate reference configurations for the connection
types to which the network performance parameters refer. This Recommendation
shows how reference configurations can be developed for the ISDN connection
types and what form such reference configurations should take.
.RT
.sp 2P
.LP
\fB2\fR \fBIntroduction\fR
.sp 1P
.RT
.sp 1P
.LP
2.1
\fIObjective\fR
.sp 9p
.RT
.PP
The general architectural model of the ISDN (see Figure\ 1/I.325) is given
in Recommendation\ I.324. The detailed network capabilities of the ISDN,
as described by connection types in Recommendation\ I.340, are described
topologically by this Recommendation giving reference configurations as
appropriate for (an) ISDN connection type(s). These reference configurations
do not give details on the number of switching nodes, length of connection,
transmission facilities used,\ etc. However, they do give the details on the
reference configuration (or topological configuration) of all matters described
by the connection type to which they refer. Therefore they should include
details on the signalling, existence of switching functions, channels,\ etc.
Based on these reference configurations, appropriate HRXs should be developed
which will be particular to network performance parameters or groups of
network performance (NP) parameters. The details on these HRXs will be
appropriate for the NP parameters in question.
.PP
In order to keep the task of developing reference configurations and the
subsequent HRXs, and the allocation of performance values to these HRXs,
to manageable proportions, it is necessary to have as limited a set as
possible of specific reference configurations. Consequently the ISDN connection
types in
Recommendation\ I.340 need to be arranged in different classes which differ
significantly from each other such that they require a separate reference
configuration model.
.RT
.LP
.rs
.sp 12P
.ad r
\fBFigure 1/I.325, (N), p.\fR
.sp 1P
.RT
.ad b
.RT
.sp 1P
.LP
2.2
\fIRelationship to other I\(hyseries Recommendations\fR
.sp 9p
.RT
.PP
The concept of reference configurations has already been used in a number
of areas of standardization of the ISDN. It is therefore necessary to
consider the concept of connection type reference configurations in the
context of these developments.
.bp
.RT
.sp 1P
.LP
2.2.1
\fIISDN architecturural model\fR
.sp 9p
.RT
.PP
It should be noted that defining a set of reference configurations presupposes
a particular architectural model of an ISDN (see Figure\ 2/I.325). The
architecturural model for the ISDN is contained in Recommendation\ I.324.
In addition, Recommendation\ I.310 on the ISDN network functional principles,
when considered together with Recommendation\ I.324, gives the general
basis of the architecture of the ISDN from which it is possible to develop
reference
configurations for ISDN connection types.
.RT
.LP
.rs
.sp 30P
.ad r
\fBFigure 2/I.325, (N), p.\fR
.sp 1P
.RT
.ad b
.RT
.sp 1P
.LP
2.2.2
\fIISDN user\(hynetwork interfaces\fR
.sp 9p
.RT
.PP
The concept of reference configurations was first used in the ISDN work
to describe the topological association of functional groupings at the
user\(hyto\(hynetwork interface points. Recommendation\ I.411 (ISDN user\(hynetwork
interfaces\ \(em\ Reference configurations) is the complete description
of these
particular reference configurations. The key factors in the definition of
reference configurations in Recommendation\ I.411 are the concepts of functional
groupings and reference points.
.RT
.sp 1P
.LP
2.2.3
\fIRecommendations X.30 and X.31 (I.461 and I.462)\fR
.sp 9p
.RT
.PP
Recommendations\ X.30 and X.32 on the adaption of X.21 and X.25
based DTEs to the ISDN also use the concept of reference configurations to
explain the topological configuration of functional groupings involved
in these kinds of terminals accessing the ISDN.
.bp
.RT
.sp 2P
.LP
\fB3\fR \fBDevelopment of the \fR \fBconcept of reference
configurations\fR
.sp 1P
.RT
.sp 1P
.LP
3.1
\fIDefinitions\fR
.sp 9p
.RT
.PP
As can be inferred from Recommendation I.411, a \fBreference\fR
\fBconfiguration\fR is defined to be \*Qa conceptual configuration based on
association rules of functional groupings and reference
points.\*U
.RT
.sp 1P
.LP
3.2
\fIPrinciples for\fR
\fIdeveloping reference configurations for\fR
\fIISDN connection types\fR
.sp 9p
.RT
.PP
Overall, the concept of the ISDN connection elements, as introduced in
Recommendations\ I.324 and\ I.340, can be effectively used to demarcate
the
different sections of the reference configuration. Because of the complicated
nature and evolutionary potential of the ISDN, it may not be possible to
internationallly specify a detailed end\(hyto\(hyend reference connection
(such as
Recommendation\ X.92 for data networks). Consequently a functional approach
is adopted to specifying the structure of the ISDN connection types and
the
associated ISDN reference configurations. In order to keep the number of
reference configurations manageable, only a restricted list of connection
types and a limited number of models of frequently realized connection
topologies are considered.
.RT
.sp 1P
.LP
3.3
\fIConnection elements\fR
.sp 9p
.RT
.PP
From the concepts of connection elements introduced in
Recommendation\ I.324 a diagram, as shown in Figure\ 3/I.325 can be developed
which can be considered as the general reference configuration of the ISDN.
It is valid for all ISDN connection types. Particular ISDN connections
may be local, national transit, international or international transit
[i.e.\ transit switched through intermediate country(ies)]. In each case
the appropriate parts of the general reference configuration would be involved.
.PP
Recommendation I.324 shows that three types of connection element have
been defined (so far):
.RT
.LP
\(em
access connection element;
.LP
\(em
national transit connection element;
.LP
\(em
international transit connection element.
.LP
.rs
.sp 16P
.ad r
\fBFigure 3/I.325, (N), p.\fR
.sp 1P
.RT
.ad b
.RT
.sp 1P
.LP
3.4
\fIFunctional groupings\fR
.sp 9p
.RT
.PP
As stated in the definition in \(sc\ 3.1 above, in order to define
reference configurations, it is necessary to define certain functional
groupings and also reference points which are the conceptual points dividing
these functional groupings.
.bp
.PP
In the description of the connection type reference configuration,
some of the major functional groupings involved can be considered under the
concept of connection related functions (CRF) as described in \(sc\ 4.2.2.1 of
Recommendation\ I.324. The concept of the CRF includes all the functional
groupings involved in establishing and controlling the connections within
the particular connection element. In the case of the international transit
connection element, two CRFs are shown in Figure\ 3/I.325 in order to retain
the symmetry of the diagram. The specific capabilities of each CRF are
not
specified in the general reference model, this is done in the reference
configuration for each group of connection types. The boundary of the CRF
should not be associated with the boundary of an exchange as these may not
correspond to each other.
.PP
Other functional groupings which are necessary for the complete
description of the connection type reference configuration include line
termination (LT), digital link, packet handling (PH) function and various
functions associated with the signalling network.
.RT
.sp 1P
.LP
3.5
\fIReference points\fR
.sp 9p
.RT
.PP
The other element involved in the description of a reference
configuration is the reference point concept. The I\(hyseries already identifies
reference points\ S and\ T (in Recommendation\ I.411) and K\dX\u, M, N\dX\uand\
P
(in Recommendation\ I.324). As can be seen from Figure\ 3/I.325, some further
internal reference points need to be identified. Further study is required
to see whether these and any further reference points need to be
defined.
.PP
In describing the reference configuration for the ISDN connection
types, an important consideration vis\(hya\(hyvis the reference points is the
following. In Figure\ 3/I.325, and the following diagrams, the end points of
the overall connection is shown as being at the T\ reference point. The
reason for this is as follows. Reference point\ S is identical to reference
point\ T
when the NT2 function is null (cf\ Recommendation\ I.411). When the NT2
function is non\(hyzero, then the performance of the overall connection
will be made up of the performance of the ISDN network connection (i.e.\
between the two interfaces at reference point\ T) and the sum of the performance
of the customer network
connections (i.e.\ between the interfaces at reference points\ S and\ T at each
end). Recommendation\ G.801 also uses this approach by defining the ends
of the digital HRX as being at the T\ reference point.
.RT
.sp 2P
.LP
\fB4\fR \fBSpecific reference configurations\fR
.sp 1P
.RT
.PP
This general reference model needs now to be associated with
specific connection types in order to develop specific reference
configurations. However, Recommendation\ I.340 allows for so many variations
in its different attributes, leading to a very large number of potential
connection types, that is necessary to consider only certain dominant
attributes in order to produce a shorter list of reference configurations.
For an initial analysis, only the first two of the four dominant attributes
listed in Recommendation\ I.340 need to be considered. Therefore the \*Qinformation
transfer mode\*U and \*Qinformation transfer rate\*U will lead to three general
classes of ISDN connection types, viz:
.RT
.LP
\(em
circuit:
.LP
\(em
64\ kbit/s,
.LP
\(em
greater than 64\ kbit/s (broadband);
.LP
\(em
packet.
.PP
The other two dominant attributes (\*Qinformation transfer\*U and
\*Qestablishment of connection\*U) do not require separate reference configurations
but will manifest themselves by different performance values.
.PP
This limited set of connection types is subsequently modelled in the associated
reference configurations taking into account a limited number of
frequently realized connection topologies.
.RT
.sp 1P
.LP
4.1
\fI64\ kbit/s class\fR
.sp 9p
.RT
.PP
This class includes connection types A1 to A12 of Table\ 2/I.340,
i.e.\ unrestricted digital, speech and 3.1\ kHz audio information transfer
susceptances and switched semi\(hypermanent and permanent
establishments.
.PP
The variation of the information transfer capability is determined by the
network performance parameter values allocated to each portion of the
connection. For example, use of digital speech interpolation in the
international connection element would restrict the connection type to
speech or 3.1\ kHz audio. Likewise, the differences between permanent
connection types and switched connection types would manifest themselves in
differences in the value of parameters such as connection establishment
time,\ etc.
.bp
.PP
This approach means that there is a small number of reference
configurations, but that all of the different connection types listed in
Recommendation\ I.340 would need to be tabulated for the allocation of
performance values.
.PP
Figure\ 4/I.325 shows the reference configuration that is proposed for
this class of ISDN connection types.
.RT
.LP
.rs
.sp 38P
.ad r
\fBFigure 4/I.325, (N), p.\fR
.sp 1P
.RT
.ad b
.RT
.sp 1P
.LP
4.2
\fIPacket class\fR
.sp 9p
.RT
.PP
Recommendation X.31 illustrates the scenarios involved in
providing packet switched capability in the ISDN. These are in fact reference
configurations for the access connection element. The possible reference
configurations for the B\(hychannel access packet mode connection type class
are shown in Figures\ 5/I.325 and\ 6/I.325.
.bp
.PP
It should be noted that the Recommendations in the X.130\(hyseries also
use the concepts of national and international portions of the connection
for the purposes of the allocation of the division of network performance
parameter values. In those cases the boundary between the national and
the international portions is in the middle of the International Data Switching
Exchange (IDSE) [or International Switching Centre (ISC)]. Further study
is required to see if this approach should be taken in the ISDN.
.RT
.LP
.rs
.sp 45P
.ad r
\fBFigure 5/I.325, (N), p. 16\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.LP
.rs
.sp 45P
.ad r
\fBFigure 6/I.325, (N), p. 17\fR
.sp 1P
.RT
.ad b
.RT
.sp 1P
.LP
4.3
\fIBroadband class\fR
.sp 9p
.RT
.PP
Further study is required to determine what the salient features of this
class of ISDN connection types are. According to Recommendation\ I.340
it would include permanent and semi\(hypermanent connections at 384, 1536
or\ 1920\ kbit/s.
.bp
.RT
.sp 2P
.LP
\fBRecommendation\ I.326\fR
.RT
.sp 2P
.sp 1P
.ce 1000
\fBREFERENCE\ CONFIGURATION\ FOR\ RELATIVE\ NETWORK\ RESOURCE |
REQUIREMENTS\fR
.EF '% Fascicle\ III.8\ \(em\ Rec.\ I.326''
.OF '''Fascicle\ III.8\ \(em\ Rec.\ I.326 %'
.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 purpose of this Recommendation is to evaluate the relative
network resource requirements associated with the provision of ISDN
telecommunication services to subscribers as they are defined in the
I.200\(hyseries.
.PP
The evaluation of relative network resource requirements and the
definition of reference configuration is the first step in cost evaluation
for ISDN services. Such cost evaluation is not covered in this
Recommendation.
.RT
.sp 2P
.LP
\fB2\fR \fBRelative resource requirements\fR
.sp 1P
.RT
.sp 1P
.LP
2.1
\fIRelation with\fR
\fIservice provision\fR
.sp 9p
.RT
.PP
For each service requested by a user the network has to provide
network resources. These network resources involve switching, signalling and
transmission capabilities. The selection of the appropriate network resource
is part of the routing function.
.PP
The combination of permissible network resources is described by the logical
concept of ISDN connection types. The list of agreed ISDN connection
types can be found in Recommendation\ I.340.
.PP
The network resources described by an ISDN connection type are given in
Figure\ 1/I.326.
.PP
The network resource has an overall scope and may imply several
subnetworks, each having to provide an appropriate part of the overall
network resource.
.RT
.LP
.sp 1
.ce
\fBH.T. [T1.326]\fR
.ce
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
lw(72p) | lw(96p) .
\(em\ Switching capability
.T&
cw(72p) | lw(96p) .
Network resource \(em\ Transmission capability
.T&
cw(72p) | lw(96p) .
\(em\ Signalling capability
_
.T&
cw(228p) .
{
FIGURE\ 1/I.326
\fBNetwork resource components\fR
}
.TE
.nr PS 9
.RT
.ad r
\fBFigure 1/I.326, (comme tableau), [T1.326], p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.sp 2
.sp 1P
.LP
2.2
\fIInformation transfer on\fR
\fInetwork resource usage\fR
.sp 9p
.RT
.PP
Information on ISDN network resources utilized and on resources
utilized of any interworked networks needs to be gathered for charging
or for accounting purposes and conveyed to possibly several points within
the
network(s). Much of this information is likely to be derived from data
carried on the signalling network (e.g.\ information associated with set\(hyup,
clear\(hydown, and/or change of status of connections). It may be passed
in batch\(hymode between Administrations or may be conveyed in real\(hytime.
.bp
.RT
.sp 2P
.LP
\fB3\fR \fBReference configuration for charging\fR
.sp 1P
.RT
.sp 1P
.LP
3.1
\fIDevelopment\fR
.sp 9p
.RT
.PP
Recommendation I.340 and other relevant Recommendations (I.310,
I.324, I.325) are considered as the starting point for the development
of the reference configuration for relative cost evaluation.
.PP
ISDN resources would be represented by network functions, as for
example:
.RT
.LP
\(em
transmission functions (local, transit) using different
techniques (digital, analogue, speech
interpolation,\ etc.);
.LP
\(em
switching functions (local, transit) for circuit\(hymode,
packet\(hymode;
.LP
\(em
interworking functions;
.LP
\(em
high layer functions.
.sp 1P
.LP
3.2
\fISituations\fR
.sp 9p
.RT
.PP
Reference configurations should include a description of the
various situations encountered in international interconnections. This
description should include the originating country, boundary, destination
country, interworking unit location, international transit.
.RT
.sp 1P
.LP
3.3
\fIReference configuration for circuit\(hymode\fR
.sp 9p
.RT
.PP
The reference configuration for circuit\(hymode ISDN connection types is
made of three connection elements:
.RT
.LP
\(em
access connection element;
.LP
\(em
national transit connection element;
.LP
\(em
international transit connection element.
.PP
The minimum relative resource requirements for international
transit connection elements are described in Table\ 1/I.326.
.LP
.sp 2
.ce
\fBH.T. [T2.326]\fR
.ce
TABLE\ 1/I.326
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(72p) | cw(84p) | cw(72p) .
Service request {
Possible resources for an international transit
connection element
} {
Relative resource requirement | ud\d\u)\d
}
_
.T&
lw(72p) | lw(84p) | cw(72p) .
1) 64 kbit/s unrestricted 64 kbit/s 1
_
.T&
lw(72p) | lw(84p) | cw(72p) .
2) Speech {
64 kbit/s, DSI/LRE
gain 5:1 | ua\d\u)\d
A/\(*m, echo control | ub\d\u)\d
} As low as 0.2
_
.T&
lw(72p) | lw(84p) | cw(72p) .
3) 3.1 kHz audio {
64 kbit/s, LRE
gain 2:1 | uc\d\u)\d
A/\(*m, echo control | ub\d\u)\d
} As low as 0.5
.TE
.LP
\ua\d\u)\d
State\(hyof\(hythe\(hyart voice processing technology is capable of
achieving a circuit gain of up to\ 5:1 on speech calls by using a
combination of digital speech interpolation (DSI) and low rate
encoding (LRE) at 32\ kbit/s. Even higher gains are conceivable
in the future with advances in LRE technology.
.LP
\ub\d\u)\d
The need for echo control in end\(hyto\(hyend ISDN connections is
under study.
.LP
\uc\d\u)\d
ISDN services when used to support voice\(hyband data via modems
cannot benefit from DSI gains.
.LP
\ud\d\u)\d
The values mentioned in the third column represent relative
resource requirements (i.e. traffic allowed in terms of bit rate
or bandwidth) and should not be interpreted as cost evaluation.
.nr PS 9
.RT
.ad r
\fBTableau 1/I.326, [T2.326], p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.sp 1P
.LP
3.4
\fIReference configuration for packet\(hymode\fR
.sp 9p
.RT
.PP
For further study.
.RT
.sp 1P
.LP
3.5
\fIReference configuration for high layer functions (HLF)\fR
.sp 9p
.RT
.PP
For further study.
.RT
.sp 1P
.LP
3.6
\fIReference configuration for additional low layer functions (ALLF)\fR
.sp 9p
.RT
.PP
For further study.
.RT
.sp 1P
.LP
3.7
\fIReference configuration for public land mobile telecommunication\fR
\fIservices\fR
.sp 9p
.RT
.PP
Reference configuration for public land mobile telecommunication
systems can be found in Recommendation\ D.93.
.RT
.LP
.rs
.sp 40P
.ad r
BLANC
.ad b
.RT
.LP
.bp
.LP
.rs
.sp 10P
.LP
\fBMONTAGE:\ \ \fR PAGE PAIRE = Blanche
.sp 1P
.RT
.LP
.bp
.sp 1P
.ce 1000
\v'3P'
SECTION\ 3
.ce 0
.sp 1P
.ce 1000
\fBNUMBERING,\ ADDRESSING\ AND\ ROUTING\fR
.ce 0
.sp 1P
.sp 2P
.LP
\fBRecommendation\ I.330\fR
.RT
.sp 2P
.sp 1P
.ce 1000
\fBISDN\ NUMBERING\ AND\ ADDRESSING\ PRINCIPLES\fR
.EF '% Fascicle\ III.8\ \(em\ Rec.\ I.330''
.OF '''Fascicle\ III.8\ \(em\ Rec.\ I.330 %'
.ce 0
.sp 1P
.ce 1000
\fI(Malaga\(hyTorremolinos, 1984; amended at Melbourne 1988)\fR
.sp 9p
.RT
.ce 0
.sp 1P
.LP
\fB1\fR \fBIntroduction\fR
.sp 1P
.RT
.PP
1.1
This Recommendation provides the general concepts, principles, and requirements
for addressing reference points located at subscriber premises,
for addressing other functions, and for allowing communications with
terminals.
.sp 9p
.RT
.PP
1.2
Recommendation\ I.331 (E.164) describes the numbering plan for
the ISDN era. Closely related information is contained in Recommendation
I.332 on numbering principles for interworking between ISDNs and dedicated
networks with different numbering plans. Recommendation I.333 on terminal
selection and Recommendation I.334 on principles relating ISDN numbersB/Fsubaddresses
to the
OSI reference model network layer addresses represent additional sources of
information having direct application to Recommendation\ I.330.
.sp 9p
.RT
.PP
1.3
The following understanding of relevant nomenclature is
established:
.sp 9p
.RT
.LP
a)
an ISDN number is one which relates to an ISDN network and
ISDN numbering plan;
.LP
b)
an ISDN address comprises the ISDN number and the mandatory
andB/For optional additional addressing information;
.LP
c)
private communications facilities are communication
capabilities confined to use by one or more particular
subscribers, as opposed to facilities which are shared by
subscribers of public networks. Examples of private
communications facilities include local area networks
(LANs), PABXs, and other private network
arrangements.
.PP
1.4
Depending on the different cases and stages identifiable
within an addressing process, an ISDN number may be (see
Figure\ 10/I.330):
.sp 9p
.RT
.LP
a)
an international ISDN number;
.LP
b)
a national ISDN number;
.LP
c)
an ISDN subscriber number.
.PP
An ISDN address comprises:
.LP
i)
the ISDN number;
.LP
ii)
mandatory andB/For optional additional addressing
information.
.bp
.PP
1.5
As an objective, all ISDNs should evolve towards a single
numbering plan, namely the ISDN numbering plan. Considering the wide
penetration of the telephone network in the world and existing telephone
network resources, the ISDN numbering plan has been developed by building
from Recommendation\ E.163. Therefore, it is recommended that the telephone
country code (TCC) be used to identify a particular country.
.FS
Country or
geographical area.
.FE
.sp 9p
.RT
.PP
1.6
An existing numbering plan may interwork and thus co\(hyexist with
the ISDN numbering plan. A framework for interworking between an ISDN and
existing numbering plans is given in Recommendation\ I.332.
Recommendations\ E.166 and\ X.122 provide information describing selected
interworking situations which have been considered by appropriate Study
Groups. Preference should be given to single stage selection methods whenever
possible.
.sp 9p
.RT
.PP
1.6.1
It is recognized that some of the present data networks, for
instance, could retain the X.121 numbering structure and interwork with
ISDNs. A critical element of such interworking is numbering plan identification.
Two approaches have been recommended:
.sp 9p
.RT
.LP
1)
the escape code method, now recognized within the format
structures of Recommendations\ E.164 and\ X.121;
.LP
2)
the NPI (Numbering Plan Identifier) method which applies
distinct protocol provisions to distinguish numbering plan
identity from address content.
.PP
Method 1) is intended for near\(hyterm applications while method 2) may
be applied to both near\(hyterm and long\(hyterm interworking, with a view
to
general use of method 2) after year\(hyend 1996.
.PP
1.6.2
It should be understood that call routing at each
switching system is guided by reference to a destination numbering plan
which is identified by either method\ 1) or method\ 2), not both. Method\
1) interprets numbers in terms of the numbering plan incorporated into
the basic operation of the switching system, unless incoming circuit class
logic or an escape code
explicitly overrides that interpretation, substituting a different numbering
plan. Under method\ 2) an explicit numbering plan identifier is presented on
each call.
.sp 9p
.RT
.PP
1.6.3
When transmission of the calling party's number is appropriate,
the numbering plan of the calling party is established in a comparable
manner. For a given direction of transmission, either method 1) is used
for both called and calling numbers or method 2) is applied in both cases.
.sp 9p
.RT
.PP
1.6.4
After a switching system selects an outgoing route, the
logical needs of the next switching system must be considered. Interworking
between numbering plans may occur. The method used to inform the subsequent
switch about applicable numbering plans may need to be adjusted, but numbering
content should not be altered. Preference should be given to method\ 2)
when it is practicable to introduce it since method\ 1) places constraints
on maximum
number length in some circumstances.
.sp 9p
.RT
.sp 2P
.LP
\fB2\fR \fBPrinciples for relating an\fR
\fBISDN number to ISDN user\(hynetwork reference configurations\fR
.sp 1P
.RT
.PP
2.1
An ISDN number shall be able unambiguously to identify (a)
particular:
.sp 9p
.RT
.LP
a)
physical interface at reference point T (see
Figure\ 1/I.330);
.LP
b)
virtual interface at reference point T; i.e.,\ for an
NT2\ +\ NT1 configuration (see Figure\ 2/I.330);
.LP
c)
multiple interfaces (physical or virtual) at reference
point\ T (see Figure\ 3/I.330);
.LP
d)
for point\(hyto\(hypoint configurations, physical interface at
reference point\ S (see Figure\ 4/I.330);
.bp
.LP
e)
for point\(hyto\(hypoint configurations, virtual interface at
reference point\ S (see Figure\ 5/I.330);
.LP
f
)
for point\(hyto\(hypoint configurations, multiple interfaces
(physical or virtual) at reference point\ S (see
Figure\ 6/I.330);
.LP
g)
for multi\(hypoint configurations (e.g. passive bus), all of
the interfaces at reference point\ S (see
Figure\ 7/I.330).
.PP
As a result, from the viewpoint of the network side of the
interface, an ISDN number is associated with one (or a multiple of) D\(hychannels
used to signal to the user.
.PP
2.2
A particular interface, or multiple of interfaces, may be
assigned more than one ISDN number. An example is shown in
Figure\ 8/I.330.
.sp 9p
.RT
.PP
2.3
All ISDNs shall be able to assign an ISDN number to an
interface at reference point\ T or\ S. However, a particular ISDN number
fulfills only one of the functions identified in \(sc\ 2.1.
.sp 9p
.RT
.PP
2.4
For mobile services an ISDN number shall be capable of
unambiguously identifying an interface in the mobile subscriber's premises,
as defined in \(sc\ 2.1 (see Figure\ 9/I.330).
.sp 9p
.RT
.PP
2.5
The ISDN number is not required to identify a particular
connection where, on a particular interface, more than one connection may be
present at a given instant.
.sp 9p
.RT
.PP
2.6
The ISDN number is not required to identify directly a particular channel,
where, within a particular interface, there may be more than one
channel. Indirect identification of particular channels may occur: e.g. when
the ISDN number identifies a particular interface and there is a one\(hyto\(hyone
correspondence between that interface and particular channels.
.sp 9p
.RT
.sp 2P
.LP
\fB3\fR \fBRelationships between ISDN number, transit network/RPOA selection
(when permitted), service indication, and quality of service indication\fR
.sp 1P
.RT
.PP
The establishment of an ISDN connection will require an ISDN
address. In addition separate non\(hyaddress related information may be
necessary for completing a connection.
.RT
.PP
3.1
Routing of ISDN connections shall take into account the
following information, when supplied by the user:
.sp 9p
.RT
.LP
a)
ISDN numbers, including destination network identification
and digits for direct dialling\(hyin (DDI) where
applicable;
.LP
b)
service identification, possibly including requested quality
of service parameters such as transit delay, throughput, and
security;
.LP
c)
multiple transit RPOA/network selection, when permitted by
the originating ISDN.
.LP
\fINote\fR \ \(em\ The need for remote transit RPOA/network selection
by the user of an ISDN which has no local transit
RPOA/network selection is for further study.
.PP
In addition, transit RPOA/network selections by the originating
ISDN, if provided, shall also be evaluated in the routing of a
connection.
.PP
In national networks on a particular connection, the user may choose to
specify some or all of this information, at either subscription time or
connection\(hyestablishment time.
.PP
The ISDN number does not identify the particular nature of the
service, type of connection, or quality of service to be used, nor does it
identify a transit RPOA/network.
.RT
.PP
3.2
In the case where an ISDN number identifies a mobile TE or a TE
served by several interfaces or networks, an ISDN may need to map from the
ISDN number on to a specific interface designation.
.bp
.sp 9p
.RT
.LP
.rs
.sp 31P
.ad r
\fBFigure 1/I.330, (MC), p. 20\fR
.sp 1P
.RT
.ad b
.RT
.LP
.rs
.sp 18P
.ad r
\fBFigure 2/I.330, (MC), p. 21\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.LP
.rs
.sp 24P
.ad r
\fBFigure 3/I.330, (MC), p. 22\fR
.sp 1P
.RT
.ad b
.RT
.LP
.rs
.sp 24P
.ad r
\fBFigure 4/I.330, (MC), p. 23\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.LP
.rs
.sp 24P
.ad r
\fBFigure 5/I.330, (MC), p. 24\fR
.sp 1P
.RT
.ad b
.RT
.LP
.rs
.sp 24P
.ad r
\fBFigure 6/I.330, (MC), p. 25\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.LP
.rs
.sp 24P
.ad r
\fBFigure 7/I.330, (MC), p. 26\fR
.sp 1P
.RT
.ad b
.RT
.LP
.rs
.sp 24P
.ad r
\fBFigure 8/I.330, (MC), p. 27\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.LP
.rs
.sp 16P
.ad r
\fBFigure 9/I.330, (MC), p. 28\fR
.sp 1P
.RT
.ad b
.RT
.sp 2P
.LP
Country or geographical area.
.FE
\fB4\fR \fBISDN number design\fR \fBconsiderations\fR
.sp 1P
.RT
.PP
4.1
Numbering plan design information is covered by
Recommendation\ I.331 (E.164).
.sp 9p
.RT
.PP
4.2
The ISDN number shall include an unambiguous identification of
a particular country
.
.sp 9p
.RT
.PP
The ISDN number is allowed to include an unambiguous
identification of a particular geographic area within a
country
.
.PP
4.3
As an objective, all ISDNs should evolve towards a single
numbering plan. However, an existing numbering plan may interwork and thus
coexist with the ISDN numbering plan.
.sp 9p
.RT
.PP
4.4
When a number of public or private ISDNs exist in a
country
, it shall not be mandatory to integrate the numbering plans of
the ISDNs. Methods for interworking are for further study, with the objective
that connections between the TEs on these various networks can be completed
by using only the ISDN address. See also Recommendatin\ I.332.
.sp 9p
.RT
.PP
4.5
The ISDN number shall be capable of containing an
identification of the ISDN
to which the called user is attached. For a private network which spans
more than one country
, the international ISDN number will cause delivery of a call to the particular
private network in the country specified by the country code.
.sp 9p
.RT
.PP
4.6
The ISDN number shall be capable of providing for interworking
of TEs on ISDNs with \*QTEs\*U on other networks. As an objective, with
respect to the ISDN number, the procedure for interworking should be the
same for all
cases. The single\(hystage method of interworking is the preferred
approach.
.sp 9p
.RT
.sp 2P
.LP
\fB5\fR \fBStructure of the ISDN address\fR
.sp 1P
.RT
.PP
5.1
The structure of the ISDN address is illustrated in
Figure\ 10/I.330. A function marking the end of the ISDN number shall always
be provided if a subaddress is present. The end of number function may
also be
provided even if no subaddress is present. When there is no subaddress
present, the end of number and end of address functions are coincident,
when used.
.sp 9p
.RT
.LP
.sp 2
.bp
.LP
.rs
.sp 14P
.ad r
\fBFigure 10/I.330, (M), p.\fR
.sp 1P
.RT
.ad b
.RT
.PP
5.2
The ISDN address may be of variable length.
.sp 9p
.RT
.sp 2P
.LP
5.3
\fIInternational ISDN number\fR
.sp 1P
.RT
.PP
5.3.1
The structure of the international number and the maximum
number length are as defined in Recommendation\ I.331 (E.164).
.sp 9p
.RT
.PP
5.3.2
In a particular international ISDN number, the exact number of
digits shall be governed by national and international requirements.
.sp 9p
.RT
.PP
5.3.3
The ISDN numbering plan shall provide substantial spare
capacity to accommodate future requirements.
.sp 9p
.RT
.PP
5.3.4
The ISDN number shall be a sequence of decimal digits.
.sp 9p
.RT
.PP
5.3.5
The ISDN number shall include the capability for direct
dialling inward where this facility is offered.
.sp 9p
.RT
.sp 2P
.LP
5.4
\fIISDN subaddress\fR
.sp 1P
.RT
.PP
5.4.1
The subaddress is a sequence of digits, the maximum length of
which shall be 20\ octets (40\ digits).
.sp 9p
.RT
.PP
5.4.2
All ISDNs shall be capable of conveying the ISDN subaddress
transparently and shall not be required to examine or operate on any of the
subaddress information.
.sp 9p
.RT
.PP
5.4.3
Special attention is drawn to the fact that subaddressing is
not to be considered as part of the numbering plan, but constitutes an
intrinsic part of ISDN addressing capabilities. The subaddress shall be
conveyed in a transparent way as a separate entity from both ISDN number and
user\(hyto\(hyuser information. See also Recommendation\ I.334.
.sp 9p
.RT
.sp 2P
.LP
\fB6\fR \fBRepresentation of ISDN address\fR
.sp 1P
.RT
.PP
6.1
At the person\(hymachine interface, the objective is to establish
one method of distinguishing between abbreviated and complete representations
of an ISDN number. This method is for further study. Internationally
recommended methods will be chosen.
.sp 9p
.RT
.PP
6.2
The method of distinguishing between an ISDN number and a
number from another numbering plan shall be by separate identification
of the applicable numbering plan. If such methods are required, internationally
recommended procedures will be chosen.
.bp
.sp 9p
.RT
.sp 2P
.LP
\fBRecommendation\ I.331\fR
.RT
.sp 2P
.sp 1P
.ce 1000
\fBNUMBERING\ PLAN\ FOR\ THE\ ISDN\ AREA\fR
.EF '% Fascicle\ III.8\ \(em\ Rec.\ I.331''
.OF '''Fascicle\ III.8\ \(em\ Rec.\ I.331 %'
.ce 0
.sp 1P
.ce 1000
\fI(Malaga\(hyTorremolinos, 1984; amended at Melbourne, 1988)\fR
.sp 9p
.RT
.ce 0
.sp 1P
.PP
See Recommendation E.164, Volume\ II, Fascicle II.2.
\v'6p'
.sp 1P
.RT
.sp 2P
.LP
\fBRecommendation\ I.332\fR
.RT
.sp 2P
.ce 1000
\fBNUMBERING\ PRINCIPLES\ FOR\ INTERWORKING\ BETWEEN\ ISDNs\fR
.EF '% Fascicle\ III.8\ \(em\ Rec.\ I.332''
.OF '''Fascicle\ III.8\ \(em\ Rec.\ I.332 %'
.ce 0
.sp 1P
.ce 1000
\fBAND\ DEDICATED\ NETWORKS\ WITH\ DIFFERENT\ NUMBERING\ PLANS\fR
.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
Different public networks currently make use of different numbering plans.
Single\(hystage interworking between ISDNs and dedicated networks as
recommended in Recommendation\ I.330 requires adoption of solutions which
make it possible to convey the addressing needs from one network to another.
.PP
This Recommendation represents a framework by which progress on
numbering plan interworking within the various CCITT Study Groups may be
coordinated. Detailed recommendations for numbering plan interworking are
contained in Recommendations\ E.166 and\ X.122.
.PP
The ISDN international number exceeds the addressing capability of
present dedicated public networks. Therefore, these networks may not be
able to reach subscribers' terminals connected to an ISDN if these terminals
make use of the 15\ digits allowed in ISDN.
.PP
In order to support numbering plan interworking between ISDNs and
present dedicated networks, procedures have to be identified which offer
single\(hystage interworking solutions for the near term, while recognizing
that other solutions supporting the 15\ digits capability of the ISDN number
will
have to be supported in the future.
.PP
One of the major objectives of introducing the concept of Time \fIT\fR |
(given in Recommendation\ E.165), is to provide a target date by which the
long\(hyterm numbering plan interworking solutions will be in place.
.RT
.sp 2P
.LP
\fB2\fR \fBPrinciples for Time T\fR
.sp 1P
.RT
.PP
ISDNs are expected to interwork with dedicated networks. However, due to
the different addressing capabilities between the ISDN and existing
numbering plans some temporary constraints need to be imposed on the number
length and digit analysis required to access the user network interfaces
of the ISDNs, before Time\ \fIT\fR .
.RT
.sp 2P
.LP
2.1
\fINumbering constraints before Time T\fR
.sp 1P
.RT
.sp 1P
.LP
2.1.1
\fIISDNs interworking with dedicated networks\fR
.sp 9p
.RT
.PP
To allow numbering plan interworking with dedicated networks before Time\
\fIT\fR , an ISDN will not assign international\ E.164 (I.331) numbers
longer
than 12\ digits to its user network interfaces capable of receiving calls
from dedicated networks.
.bp
.RT
.sp 1P
.LP
2.1.2
\fIISDNs which do not interwork with dedicated networks\fR
.sp 9p
.RT
.PP
These ISDNs are allowed to assign numbers to user network
interfaces according to the full capability of the numbering plan for the
ISDN era.
.RT
.sp 1P
.LP
2.2
\fIEvolution after Time T\fR
.sp 9p
.RT
.PP
After Time \fIT\fR , ISDNs and PSTNs can make use of the full capability
of E.164 numbers to identify their user network interfaces and terminals
respectively.
.RT
.sp 1P
.LP
2.3
\fIEvolution up to Time T\fR
.sp 9p
.RT
.PP
Between now and Time \fIT\fR , any new network or user equipment, in
ISDNs, or networks intending to interwork with ISDNs, should be installed
with the identified relevant post\(hy\fIT\fR capability(ies).
.RT
.sp 2P
.LP
\fB3\fR \fBSingle\(hystage interworking between ISDNs and dedicated
networks\fR
.sp 1P
.RT
.PP
3.1
Numbering plan interworking procedures for short\(hyterm and for
long\(hyterm will be required between:
.sp 9p
.RT
.LP
i)
ISDN (E.164) to/from PSPDN (X.121)
.LP
ii)
ISDN (E.164) to/from CSPDN (X.121)
.LP
\fINote\fR \ \(em\ Requirements for Telex (F.69) are inc
luded in
Recommendation\ U.202.
.PP
As defined in Recommendation\ I.451\ (Q.931).
.FE
3.2
The recommended long\(hyterm numbering plan interworking solution is based
on the NPI/TON field in the ISDN call set\(hyup message.
The NPI elements is the numbering plan identifier
(e.g.\ Recommendations\ E.164/E.163, X.121, F.69), whereas the TON indicates
the type of number (e.g.\ local, national, international). This
NPI/TON field
will be carried as part of the call set\(hyup message to
the originating exchange, which will use this information to route the call.
The NPI element will also be available within the network as part of the
Initial Address Message in Recommendation\ Q.763.
.sp 9p
.RT
.PP
An equivalent NPI/TON feature in Recommendations\ X.25/X.75 will
also be available to support long\(hyterm numbering plan interworking between
ISDNs and PSPDNs, employing X.31 procedures.
.PP
3.3
The short\(hyterm, single\(hystage interworking arrangements will use
prefixes and escape codes to indicate the type of number and the numbering
plan of the destination network, respectively. Definitions of prefixes
and escape
codes are provided in Annex\ A. As indicated in Annex\ A, prefixes are
not part of the number and are not signalled over internetwork or international
boundaries to that they are not subject to international standards. Escape
codes however, may be carried forward through the originating network and
across internetwork and international boundaries Therefore, the values of
escape codes need to be standardized.
.sp 9p
.RT
.PP
\fINote\fR \ \(em\ The details on short\(hyterm interworking using escape
codes are included in Recommendations\ E.166 and\ X.122.
.PP
3.4
Table\ 1/I.332 illustrates numbering considerations for
single\(hystage interworking using the example of interworking between
an ISDN and\ PDN.
.bp
.sp 9p
.RT
.sp 1P
.LP
3.5
\fIPrinciples for\fR
\fIconsistent interworking\fR
.sp 9p
.RT
.PP
When considering Table\ 1/I.332, the following points should be
taken into account:
.RT
.LP
1)
It should be noted that X.25 procedures (containing E.164
numbers) may be used on ISDN subscriber\(hyto\(hyISDN subscriber
calls where no PDN is used. The choice of method for
X.25/X.75 should allow this application.
.LP
2)
During the interim period (pre\(hy\fIT\fR ), ISDN interfaces
not interworking with any existing dedicated networks may be
assigned E.164 numbers up to 15\ digits in length. (Other
ISDN subscribers would be assigned\ E.164 numbers according
to Table\ 1/I.332).
.LP
3)
The treatment of various addresses during call interworking,
as outlined in Table\ 1/I.332, should apply to all
kinds of addresses, e.g.\ calling party,
redirecting,\ etc.
.ce
\fBH.T. [T1.332]\fR
.ce
TABLE\ 1/I.332
.ce
\fBAccommodation of numbers during ISDN/PDN
.ce
interworking\fR
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(30p) | cw(42p) | cw(78p) | cw(78p) .
Call type Man machine selection User\(hynetwork interface Gatenay between networks
_
.T&
lw(30p) | lw(42p) | lw(78p) | lw(78p) .
ISDN to PDN Terminal specific {
\fIInterim\fR
\fR
Recs. E.166 and X.122
or
long\(hyterm solution
\fIBy time T\fR
Numbering plan\ = Rec. X.121
Number = DNIC (DCC + NN)
+ NTN
Type of number:
international (DNIC present),
national (DNIC omitted),
or network specific
} {
\fIInterim\fR
Recs. E.166 and X.122
or
long\(hyterm solution
\fIBy time T\fR
Numbering plan\ = Rec. X.121
Number = DNIC (DCC + NN)
+ NTN
Type of number:
international (DNIC present),
national (DNIC omitted),
or network specific
}
_
.T&
lw(30p) | lw(42p) | lw(78p) | lw(78p) .
PDN to ISDN e.g. Request for PAD {
e.g Recs. X.25/X.31, X.21/X.30
} e.g Recs. X.75, X.71
.T&
lw(30p) | lw(42p) | lw(78p) | lw(78p) .
{
PAD/DTE implementation specific for
support of user\(hynetwork interface
} {
\fIInterim\fR
Modified X\(hySeries to
support Rec.\ I.330 principles
Numbering plan\ = Rec. E.164
(CC\ +\ NDC\ +\ SN) \(=\ 12 digits
\fIBy time T\fR
Modified Recs. X.25 and I.451
to support long\(hyterm interworking
solution
Numbering plan\ = Rec. E.164
(CC\ +\ NDC\ +\ SN) \(=\ 15 digits
} {
\fIInterim\fR
Modified X\(hySeries to support
Rec. I.330
principles
Numbering plan\ = Rec. E.164
(CC\ +\ NDC\ +\ SN) \(=\ 12 digits
\fIBy time T\fR
Modified Recs. X.25, X.75 and Q.763
to support long\(hyterm interworking
solution
Numbering plan\ = Rec. E.164
(CC\ +\ NDC\ +\ SN) \(=\ 15 digits
}
_
.T&
lw(18p) | lw(102p) | lw(18p) | lw(90p) .
CC Country code NDC National destination code
.T&
lw(18p) | lw(102p) | lw(18p) | lw(90p) .
SN Subscriber number DNIC {
Data network identification code
}
.T&
lw(18p) | lw(102p) | lw(18p) | lw(90p) .
DCC Data country code NN National number
.T&
lw(18p) | lw(102p) | lw(18p) | lw(90p) .
NTN Network terminal number
.TE
.LP
\fINote\ 1\fR
\ \(em\ Numbering plan interworking between ISDNs and between ISDN
and PSTN is not required since a common numbering plan is used.
.LP
\fINote\ 2\fR
\ \(em\ Other solutions at particular interfaces may \fIalso\fR
be supported
by some networks. Such solutions should not conflict with the use of the
indicated method. The method indicated should be supported by all
networks.
.RT
.ad r
\fBTableau 1/I.332 [T1.332], p. \fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.sp 2P
.LP
\fB4\fR \fBRequirements by Time T\fR
.sp 1P
.RT
.PP
4.1
By Time \fIT\fR | the numbering plan identifier and type of number
(NPI/TON)
capability should be exploited for calls within the ISDN and
between ISDN and a dedicated network (e.g.\ PSPDN
.FS
Introduction of NPI may
take place prior to Time\ \fIT\fR , provided that no burden is placed on
networks not supporting the NPI when interworking unless bilaterally agreed.
.FE
in the
following cases:
.sp 9p
.RT
.LP
i)
NPI/TON must be used across internetwork and international
boundaries where Signalling System No.\ 7 ISUP is used;
.LP
ii)
the NPI/TON equivalent feature in the X.25 packet layer
must be used when interworking from ISDN to a PSPDN
employing X.31 procedures. (Reference
Table\ 1/I.332)
.PP
4.2
Where ISDN is provided such that there is a mixture of PSTN and
ISDN customers and traffic on a local exchange, the manner in which NPI/TON
is used in the network is at the discretion of the Administration, taking
due
account of prevailing commercial, technical and regulatory considerations.
Although Time\ \fIT\fR is not directly relevant to this decision, networks
not fully exploiting the NPI/TON capability after \fIT\fR shall place no
burden on those
that do.
.sp 9p
.RT
.PP
4.3
In those parts of a PSTN where inter\(hyexchange signalling is
other than Signalling System No.\ 7 ISUP, prefixes/escape digits may have to
continue to be used.
\v'1P'
.sp 9p
.RT
.ce 1000
ANNEX\ A
.ce 0
.ce 1000
(to Recommendation I.332)
.sp 9p
.RT
.ce 0
.ce 1000
\fBPrefixes and escape codes for numbering plan interworking\fR
.sp 1P
.RT
.ce 0
.LP
A.1.
\fIPrefix\fR
.sp 1P
.RT
.PP
The prefix is an indicator consisting of one or more digits,
allowing the selection of different types of address formats (e.g.\ local,
national, or international address formats), transit network and/or service
selection. Prefixes are not part of the number and are not signalled over
internetwork or international boundaries.
.PP
\fINote\fR \ \(em\ When prefixes are used, they are always entered by the
user or automatic calling equipment.
.RT
.sp 1P
.LP
A.2
\fIEscape code\fR
.sp 9p
.RT
.PP
An escape code is an indicator consisting of one or more digits.
The indicator is defined in a given numbering plan, and is used to indicate
that the following digits are a number from a different numbering plan.
Escape codes are currently established within the\ X.121 and\ E.164 numbering
plans.
.PP
An escape code may be carried forward through the originating network and
can be carried across internetwork and international boundaries. Therefore,
the digits for escape codes should be standardized.
.PP
\fINote\fR \ \(em\ There may be cases when a standardized escape code may be
numerically equal to a prefix already in use in the network. In this case a
different digit (special prefix) other than the standardized escape code
may be used, and the translation from the \*Qspecial prefix\*U to the standardized
escape code is performed by the network.
.RT
.LP
.sp 1
.bp