Internet Standards/CD2.mdf/ccitt/1992/i/i413.asc

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INTERNATIONAL  TELECOMMUNICATION  UNION





CCITT    I.413

THE  INTERNATIONAL

TELEGRAPH  AND  TELEPHONE

CONSULTATIVE  COMMITTEE







INTEGRATED  SERVICES

DIGITAL  NETWORK  (ISDN)

OVERALL  NETWORK  ASPECTS  AND  FUNCTIONS,

ISDN  USER-NETWORK  INTERFACES







B-ISDN  USER-NETWORK  INTERFACE











Recommendation  I.413











Geneva, 1991













































































Printed in Switzerland

















FOREWORD



    The CCITT (the International Telegraph and Telephone Consultative Committee) is a permanent organ of the Interna-
tional Telecommunication Union (ITU). CCITT is responsible for studying technical, operating and tariff questions and issuing
Recommendations on them with a view to standardizing telecommunications on a worldwide basis.

    The Plenary Assembly of CCITT which meets every four years, establishes the topics for study and approves
Recommendations prepared by its Study Groups. The approval of Recommendations by the members of CCITT
between Plenary Assemblies is covered by the procedure laid down in CCITT Resolution No. 2 (Melbourne, 1988).

    Recommendation I.413 was prepared by Study Group XVIII and was approved under the Resolution No.
2 procedure on the 5th of April 1991.





___________________









CCITT  NOTES



1)    In this Recommendation, the expression "Administration" is used for conciseness to indicate both a telecommunica-
tion Administration and a recognized private operating agency.

2)    A list of abbreviations used in this Recommendation can be found in Annex A.



















aITU1991

All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic or
mechanical, including photocopying and microfilm, without permission in writing from the ITU.





    Preamble to B-ISDN Recommendations

    In 1990, CCITT SG XVIII approved a first set of Recommendations on B-ISDN. These are:

I.113 û Vocabulary of terms for broadband aspects of ISDN

I.121 û Broadband aspects of ISDN

I.150 û B-ISDN asynchronous transfer mode functional characteristics

I.211 û B-ISDN service aspects

I.311 û B-ISDN general network aspects

I.321 û B-ISDN Protocol Reference Model and its application

I.327 û B-ISDN functional architecture

I.361 û B-ISDN ATM Layer specification

I.362 û B-ISDN ATM Adaptation Layer (AAL) functional description

I.363 û B-ISDN ATM Adaptation Layer (AAL) specification

I.413 û B-ISDN user-network interface

I.432 û B-ISDN user-network interface - Physical Layer specification

I.610 û Operation and maintenance principles of B-ISDN access

    These Recommendations address general B-ISDN aspects as well as specific service- and network-ori-
ented issues, the fundamental characteristics of the asynchronous transfer mode (ATM), a first set of relevant
ATM oriented parameters and their application at the user-network interface as well as impact on operation
and maintenance of the B-ISDN access. They are an integral part of the well established I-Series Recommen-
dations. The set of Recommendations are intended to serve as a consolidated basis for ongoing work relative to
B-ISDN both within CCITT and in other organizations. They may also be used as a first basis towards the devel-
opment of network elements.

    CCITT will continue to further develop and complete these Recommendations in areas where there are
unresolved issues and develop additional Recommendations on B-ISDN in the I-Series and other series in the
future.









PAGE BLANCHE



Recommendation I.413

Recommendation I.413



B-ISDN  USER-NETWORK  INTERFACE





1    Introduction

    This Recommendation gives the reference configuration for the B-ISDN user-network interface (UNI) and
examples of physical realizations. It describes Physical Layer information flows according to the B-ISDN Proto-
col Reference Model and identifies interface functions. It also addresses OAM issues as they relate to the refer-
ence configuration at the user access and to the interface specifications.





2    Reference configuration at the user-network interface

2.1    Functional groups and reference points

    The reference configurations defined in Figure 1/I.411 for ISDN basic access and primary access are
considered general enough to be applicable to all aspects of the B-ISDN accesses.

    Figure 1/I.413 shows the B-ISDN reference configurations which contain the following:

û    functional groups: B-NT1, B-NT2, B-TE1, TE2, B-TE2 and B-TA;

û    reference points: TB, SB and R.

    In order to clearly illustrate the broadband aspects, the notations for reference points and for func-
tional groups with broadband capabilities are appended with the letter B (e.g., B-NT1, TB). The broadband func-
tional groups are equivalent to the functional groups defined in Recommendation I.411. Interfaces at the R
reference point may or may not have broadband capabilities.

    Interfaces at reference points SB and TB will be standardized. These interfaces will support all ISDN
services.





Figure 1/I.413  =   8 cm









2.2    Examples of physical realizations

    Figure 2/I.413 gives examples of physical configurations illustrating combinations of physical interfaces at
various reference points. The examples cover configurations that could be supported by standardized interfaces
at reference points SB and TB. Other configurations may also exist. For example, physical configurations of B-
NT2 may be distributed or use shared medium to support local area network (LAN) emulation and other appli-
cations.

    Figure 3/I.413 illustrates possible physical configurations, but does not preclude alternative configu-
rations. Whether a single interface at the SB reference point can cover different configurations as illustrated on
Figure3/I.413 is for further study.

    Figures 2a/I.413 and 2b/I.413 show separate interfaces at the SB and TB reference points; Figures 2c/
I.413 and 2d/I.413 show an interface at SB but not at TB; Figures 2e/I.413 and 2f/I.413 show an interface at TB
but not at SB; Figures 2g/I.413 and 2h/I.413 show separate interfaces at S, SB and TB; Figures 2i/I.413 and 2j/
I.413 show interfaces at SB and TB which are coincident.

    Additionally, Figures 2b/I.413, 2d/I.413, 2f/I.413, 2h/I.413 and 2j/I.413 show an interface at reference
pointR.



2.3    Basic characteristics of the interfaces at TB and SB reference points

2.3.1    Characteristics of the interfaces at 155.520 Mbit/s

2.3.1.1    Interface at TB reference point

    There are two options for the interface at the physical layer: a cell-based physical layer and an SDH-
based physical layer. The ATM layer is common to these two options.

    There is only one interface per B-NT1 at the TB reference point. The operation of the physical medium
is point-to-point in the sense that there is one sink (receiver) in front of one source (transmitter).

    When point-to-multipoint configurations at TB are used as an option at ATM and higher layers, their
implications at these layers and the physical layer have to be studied.

2.3.1.2    Interface at the SB reference point

    One or more SB interfaces per B-NT2 are present. The interface at the SB reference point is point-to-point
at the physical layer in the sense that there is only one sink (receiver) in front of one source (transmitter)
and may be point-to-multipoint at the other layers.

    Further study is required to determine whether it is feasible to have a unique interface at the SB ref-
erence point to achieve terminal interchangeability.





Figure 2/I.413 =  =  Page pleine













Figure 3/I.413 =  =  Page pleine









2.3.1.3    Relationship between interfaces at SB and TB

    Configurations described in Figures 2i/I.413 and 2j/I.413 require that the interface specifications at TB and
SB have a high degree of commonality, in order to ensure that a simple broadband terminal may be connected
directly to the TB interface.

    The feasibility of achieving the needed commonality requires further study.

2.3.2    Characteristics of the interfaces at 622.080 Mbit/s

    For further study.



2.4    Relationship between ISDN interfaces

    Figures 2g/I.413 and 2h/I.413 show configurations where B-ISDN and ISDN interfaces may occur at SB andS
respectively. In this case B-NT2 functionalities have to ensure the interface capabilities for both S and SB.
Other configurations for supporting terminals at the interface at the S reference point may exist.

2.5    Application of B-ISDN model to functional groups

2.5.1    General

    Lists of functions for each functional group are given below. Each particular function is not necessarily
restricted to a single functional group. For example, "interface termination" functions are included in the
function lists of B-NT1, BNT2 and B-TE. The function lists for B-NT1, B-NT2, B-TE and B-TA are not exhaus-
tive. Not all specific functions in a functional group need to be present in all implementations.

    A complete description of the functional groups remains for further study.

2.5.2    Network termination 1 (B-NT1) for B-ISDN

    This functional group includes functions broadly equivalent to layer 1 of the OSI reference model. Examples
of B-NT1 functions are:

û    line transmission termination;

û    transmission interface handling;

û    OAM functions.

    Additional functions specific to the transmission system may be required. The means of powering of
implementations of the B-NT1 is for further study. When the B-NT1 terminates cell-based OAM flows, cell
delineation is required.

2.5.3    Network termination 2 (B-NT2) for B-ISDN

    This functional group includes functions broadly equivalent to layer 1 and higher layers of the Recommen-
dation X.200 reference model. B-NT2 can be null in the case of commonality between TB and SB.

    Examples of B-NT2 functions are:

û    adaptation functions for different media and topologies (MA functions);

û    functions of a distributed B-NT2;

û    cell delineation;

û    concentration;

û    buffering;

û    multiplexing/demultiplexing;

û    resource allocation;

û    usage parameter control;

û    adaptation layer functions for signalling (for internal traffic);

û    interface handling (for the TB and SB interfaces);

û    OAM functions;

û    signalling protocol handling;

û    switching of internal connections.

    B-NT2 implementations may be concentrated or distributed. In a specific access arrangement, the B-
NT2 may consist only of physical connections. When present, implementations of the B-NT2 are locally powered.

2.5.4    Terminal equipment (B-TE) for B-ISDN

    This functional group includes functions broadly belonging to layer 1 and higher layers of the Recommen-
dation X.200 reference model.

    Examples of B-TE functions are:

û    user/user-and-user/machine dialogue and protocol;

û    interface termination and other layer 1 functions;

û    protocol handling for signalling;

û    connection handling to other equipments;

û    OAM functions.

    The possibility of powering the B-TE via the SB interface is for further study.

2.5.4.1    Terminal equipment type 1 (B-TE1) for B-ISDN

    This functional group includes functions belonging to the B-TE functional group with an interface that
complies with the B-ISDN SB and/or TB interface Recommendations.

2.5.4.2    Terminal equipment type 2 (B-TE2) for B-ISDN

    This functional group includes functions belonging to the functional group B-TE but with a broadband
interface that complies with interface Recommendations other than the B-ISDN interface Recommendations or
interfaces not included in CCITT Recommendations.

2.5.5    Terminal adaptor (B-TA) for B-ISDN

    This functional group includes functions broadly belonging to layer 1 and higher layers of the Recommen-
dation X.200 reference model that allow a TE2 or a B-TE2 terminal to be served by a B-ISDN user-network
interface.





3    Physical layer information flows and interface functions

    Physical layer functions and physical layer primitives are defined in Recommendation I.321, _ 4.2. The
present section defines the information flows between the physical medium (PM), the transmission convergence
sublayer (TC) and their adjacent entities (ATM layer and management plane). The information flows identified
here do not imply any physical realization. Information flows identified in this section may not be exhaustive.

3.1    Relation with other sublayers or entities

    The information flows specified in the following subsections will be provided in Recommendation I.321 by
primitives. Further study is required to specify these primitives.

3.1.1    Information exchanged between the PM and the TC sublayers

a)    From the PM sublayer to the TC sublayer:

    The PM sublayer provides at least the following information to the TC sublayer:

û    a flow of logical symbols (e.g., bits),

û    associated timing information.

b)    From the TC sublayer to the PM sublayer:

    The TC sublayer provides at least the following information to the PM sublayer:

û    a flow of logical symbols (e.g., bits),

û    associated timing information.

3.1.2    Information exchanged between the physical layer and the ATM layer

a)    From the physical layer to the ATM layer 1) :

    The physical layer provides at least the following information  to the ATM layer:

û    valid cells (excluding idle cells and physical layer OAM cells),

û    associated timing (e.g., presence of data and clock information).

b)    From the ATM layer to the physical layer:

û    assigned and unassigned cells if any available,

û    associated timing (e.g., presence of data and clock information).

    In case no cells are available, no data are transferred and the physical layer inserts idle cells to build up
the data flow to be transmitted.

3.1.3    Information exchanged between the physical layer and the management plane

a)    From the physical layer to the management plane:

û    loss of incoming signal,

û    indication of received errors or indication of degraded error performance.

    Detection of bit errors may be based on received unexpected code violations or other bit error detecting
schemes.

    In addition, other information may be provided to the management plane. This if for further study.

b)    From the management plane to the physical layer:

    For further study.

3.2    Modes of operation

    Normal mode: "fully active".

    Other modes, e.g., emergency mode in case of power failure or deactivated mode in order to save
power are for further study.



3.3    Interface function

3.3.1    Data transfer

    The user information together with the information for connection related functions (e.g., signalling) are
carried in ATM cells. OAM information related to the physical layer is carried in transmission overheads or PL-
OAM cells, depending on the transmission structure used (SDH-based or cell-based) and on the functional
entity concerned.

3.3.2    Timing

    Bit timing has to be provided according to Recommendation I.432.

3.3.3    Bit sequence independence

    The PM and the associated transmission system payload have to provide bit sequence independence.

3.3.4    Provision of power feeding

    For further study.

3.3.5    Activation/deactivation

    For further study.





4    UNI related OAM functions

    The following OAM functions associated with the UNI have been identified and are described in Recommen-
dation I.610:

1)    transmission and reception of maintenance signals (e.g., alarm indication signal (AIS) and far end receive
failure (FERF));

2)    performance monitoring;

3)    control communication provisions.

    Some overhead capacity has to be allocated to these functions, but the exact implementation depends
on the physical layer option selected, i.e. whether it is SDH-based or cell-based. Implementation of these
maintenance functions is described in Recommendation I.432. The definition of maintenance signals required
for the supervision of cell delineation and header error performance is for further study.

ANNEX  A

(to Recommendation I.413)

Alphabetical list of abbreviations used

in this Recommendation



AIS        Alarm indication signal

B-NT        Network termination for B-ISDN

B-NT1        Network termination 1 for B-ISDN

B-NT2        Network termination 2 for B-ISDN

B-TA        Terminal adaptor for B-ISDN

B-TE        Terminal equipment for B-ISDN

FERF        Far end receive failure

LAN        Local area network

MA        Medium adaptor

TA        Terminal adaptor

TC        Transmission convergence sublayer

UNI        User-network interface