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FOREWORD
The CCITT (the International Telegraph and Telephone Consultative
Committee) is the permanent organ of the International Telecommu-
nication 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 pre-
pared 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 G.781 was prepared by Study Group XV and was
approved under the Resolution No. 2 procedure on the 14 of December
1990.
___________________
CCITT NOTE
In this Recommendation, the expression ôAdministrationö is used for
brevity to indicate both a telecommunication Administration and a
recognized private operating agency.
πITU1990
All rights reserved. No part of this publication may be reproduced or uti-
lized in any form or by any means, electronic or mechanical, including pho-
tocopying and microfilm, without permission in writing from the ITU.
PAGE BLANCHE
Recommendation G.781
Recommendation G.781
STRUCTURE OF RECOMMENDATIONS ON MULTIPLEXING
EQUIPMENT FOR THE SYNCHRONOUS DIGITAL HIERARCHY
(SDH)
1 General
Recommendations G.707, G.708 and G.709 provide details of the bit
rate, format, multiplexing structure and payload mappings for the Synchro-
nous Digital Hierarchy (SDH).
Recommendations giving the characteristics of multiplexing equip-
ment for the SDH are structured to take into consideration the following:
i) in order not to constrain equipment design, there is a need to
describe equipment characteristics in terms of functions in such a
way as to avoid specifying particular implementations of those
functions;
ii) multiplexing equipment functionality can be usefully partitioned
into a number of areas and the Recommendation structure reflects
this partitioning;
iii) some functions specified for multiplexing equipment may also be
applicable to Recommendations on other SDH equipments and
these latter Recommendations may make reference to Recommen-
dations on multiplexing equipment, thus avoiding duplication of
text and ensuring consistency of specification over a number of
different equipments.
2 Structure of Recommendations
Taking into account the above points, the structure of Recommenda-
tions for synchronous multiplexing equipment is as follows:
ù G.781 Structure of Recommendations on multiplexing equipment
for the Synchronous Digital Hierarchy (SDH)
ù G.782 Types and general characteristics of Synchronous Digital
Hierarchy (SDH) multiplexing equipment
ù G.783 Characteristics of Synchronous Digital Hierarchy (SDH)
multiplexing equipment functional blocks
ù G.784 Synchronous Digital Hierarchy (SDH) management
3 Options
Information and guidance on optional features contained in SDH Rec-
ommendations is given in the AnnexA.
ANNEX A
(to Recommendation G.781)
Considerations relating to the selection of optional features
The Recommendations on SDH (G.707, G.708, G.709, G.781, G.782,
G.783, G.784, G.957, G.958) provide a foundation towards ensuring a high
degree of harmonization, and therefore inter-operability potential, between
different practical implementations of the functions described in the Recom-
mendations. However, it is important to note that the Recommendations
contain a number of optional features, some of which are important to con-
sider carefully in order to ensure inter-operability.
In selecting a consistent set of optional features, the following situations
will need to be taken into account:
ù single network operator's domain, even when using a single suppli-
er's implementation of SDHequipment;
ù single network operator's domain, when using multiple suppliers'
implementations;
ù inter-operation between different network operators' domains.
In the detailed design, implementation and operation of their net-
works, it is important that network operators make appropriate selections of
optional features, and reach an understanding with their equipment suppliers
and with other network operators to ensure that an appropriate level of inter-
operability is achieved.
In terms of suppliers, it will be essentially a commercial judgement
whether they choose to offer a particular option. In order to limit the number
of variations, when an optional feature is provided, it should be in accor-
dance with the recommended approach.
INTERNATIONAL TELECOMMUNICATION UNION
CCITT G.781
THE INTERNATIONAL
TELEGRAPH AND TELEPHONE
CONSULTATIVE COMMITTEE
GENERAL ASPECTS OF DIGITAL
TRANSMISSION SYSTEMS
TERMINAL EQUIPMENTS
STRUCTURE OF RECOMMENDATIONS ON MULTI-
PLEXING EQUIPMENT FOR
THE SYNCHRONOUS DIGITAL
HIERARCHY (SDH)
Recommendation G.781
Geneva, 1990