Internet Standards/CD2.mdf/ccitt/1992/i/i464.asc

Text File | 1994-01-30 | 7KB | 273 lines

         INTERNATIONAL  TELECOMMUNICATION  UNION







         CCITT                                               I.464

         THE  INTERNATIONAL
         TELEGRAPH  AND  TELEPHONE
         CONSULTATIVE  COMMITTEE







         INTEGRATED  SERVICES
         DIGITAL  NETWORK  (ISDN)

         OVERALL  NETWORK  ASPECTS
         AND  FUNCTIONS,
         ISDN  USER-NETWORK  INTERFACES


         MULTIPLEXING,  RATE  ADAPTION
         AND  SUPPORT  OF  EXISTING
         INTERFACES  FOR  RESTRICTED
         64  kbit/s  TRANSFER  CAPABILITY


         Recommendation  I.464




         Geneva, 1991









































































                                             Printed in Switzerland










                             FOREWORD

       The   CCITT  (the  International  Telegraph  and   Telephone
Consultative  Committee) is a permanent organ of the  International
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.464 was prepared by Study Group XVIII and was
approved  under  the  Resolution No. 2 procedure  on  the  25th  of
October 1991.





                        ___________________






                            CCITT  NOTE

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



















                           π  ITU  1991

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.



PAGE BLANCHE



Recommendation I.464
Recommendation I.464

     MULTIPLEXING,  RATE  ADAPTION  AND  SUPPORT  OF  EXISTING
   INTERFACES  FOR  RESTRICTED  64  kbit/s  TRANSFER  CAPABILITY

   (Malaga-Torremolinos 1984: amended at Melbourne, 1988 and in
                           Geneva, 1991)

      Restricted  64 kbit/s transfer capability is defined  as  ô64
kbit/s octet-structured capability with the restriction that an all-
zero octet is not permittedö.

      The  procedures given in Recommendations I.460,  I.461(X.30),
I.462(X.31),  I.463(V.110)  and  I.465(V.120)  for  rate  adaption,
multiplexing and support of existing interfaces for 64 kbit/s,  are
fully  compatible with the restricted 64 kbit/s transfer capability
except for the following limitations:
     i)For  time  division  multiplexing, the eighth  bit  of  each
        octet of the 64 kbit/s stream will be set to binary 1. This
        procedure  is  the  same  as that used  for  time  division
        multiplexing  into an unrestricted 64 kbit/s channel  where
        the full 64 kbit/s is not utilized.
     ii)   For  adapting  X.25 DTEs as described in  Recommendation
        I.462(X.31)  where rate adaption (º 7.3.2 of Recommendation
        X.31)  is accomplished by "flag stuffing" or adapting  DTEs
        for   circuit   mode   as   described   in   Recommendation
        I.465(V.120),  for use with restricted 64  kbit/s  transfer
        capabilities, the data is first rate adapted to a 56 kbit/s
        rate  and  the  resulting  bit  stream  is  placed  into  a
        64  kbit/s channel using the first seven bits of each  byte
        with  the  eighth bit of each byte set to a  binary  1.  An
        alternative  approach,  which  uses  the  full  64   kbit/s
        capacity of the transport capability and which may be  used
        by mutual agreement, is described in Appendix I.

      The  procedures in Recommendation I.462(X.31) apply  only  to
synchronous terminals.

      The  procedures  in  Recommendations I.460,  I.461(X.30)  and
I.463(V.110)  apply to both synchronous and asychronous terminals.

       The  procedures  in  Recommendation  I.465(V.120)  apply  to
synchronous   HDLC   based,  synchronous   bit   transparent,   and
asynchronous terminals.



                            APPENDIX I

                     (to Recommendation I.464)

     HDLC inverted mode for restricted transport capabilities



      Inverted  HDLC  is  adequate for  the  transmission  of  data
sequences using HDLC based protocols (i.e. Recommendations X.25 and
V.120)  over  B-channel  connections independent  of  whether  such
connection is restricted or unrestricted. In the inverted  mode,  a
binary  1 is sent as a pulse and a binary 0 is sent as the  absence
of  a  pulse. An "abort" must be restricted to a sequence of  seven
consecutive  binary 1s and on all binary 1s idle must  be  sent  as
repeated transmission of a sequence of seven consecutive binary  1s
followed  by  a binary 0. The all 1s idle appears as  a  string  of
continuous  aborts.  A  receiver, which must  distinguish  the  all
binary  1s idle, shall interpret two or more consecutive aborts  as
idle. Where continuous aborts cause difficulties, the receiver must
include  the capability of converting continuous aborts to  an  all
binary 1s idle.

      For  basic  access, when the used B-channel is not connected,
the  TE  must send all 1s. When the B-channel is connected, the  TE
shall  initiate  the transmission of interframe time  fill  (flags)
immediately.