C:\WINWORD\CCITTREC.DOT



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.





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CCITT  NOTE

	In this Recommendation, the expression “Administration” is used for 
brevity to indicate both a telecommunication Administration and a 
recognized private operating agency.



















ăITU1990

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:

—	G.781	Structure of Recommendations on multiplexing equipment 
for the Synchronous Digital Hierarchy (SDH)

—	G.782	Types and general characteristics of Synchronous Digital 
Hierarchy (SDH) multiplexing equipment

—	G.783	Characteristics of Synchronous Digital Hierarchy (SDH) 
multiplexing equipment functional blocks

—	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:

—	single network operator's domain, even when using a single suppli-
er's implementation of SDHequipment;

—	single network operator's domain, when using multiple suppliers' 
implementations;

—	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