Internet Standards/CD2.mdf/ccitt/1992/a/a20.asc

Text File | 1994-01-30 | 8KB | 156 lines

2     Fascicle VIII.2 ù Rec. A.20

                                    Fascicle VIII.2 ù Rec. A.20   1


     PRINCIPLES GOVERNING THE COLLABORATION BETWEEN THE CCITT
        AND OTHER INTERNATIONAL ORGANIZATIONS IN THE STUDY
                      OF DATA COMMUNICATIONS


 Recommendation A.20 published in Volume I is reproduced below for
                                the
    convenience of the reader of the Series X Recommendations.



Recommendation A.20

       COLLABORATION WITH OTHER INTERNATIONAL ORGANIZATIONS
                      OVER DATA TRANSMISSION

          (Geneva, 1964; amended at Mar del Plata, 1968;
      Geneva, 1972, 1976 and 1980; MalagaùTorremolinos, 1984)


     The CCITT,

considering

      (a)    that, according to Article 1 of the agreement  between
the  United Nations and the International Telecommunication  Union,
the  United  Nations recognizes the International Telecommunication
Union  as the specialized agency responsible for taking such action
as   may  be  appropriate  under  its  basic  instrument  for   the
accomplishment of the purposes set forth therein;

      (b)    that  Article 4 of the International Telecommunication
Convention  (Nairobi, 1982) states that the purposes of  the  Union
are:
     ôa)   to maintain and extend international cooperation between
        all  Members of the Union for the improvement and  rational
        use  of  telecommunications of all kinds,  as  well  as  to
        promote  and  to offer technical assistance  to  developing
        countries in the field of telecommunications;
     ôb)   to  promote the development of technical facilities  and
        their most efficient operation with a view to improving the
        efficiency of telecommunication services, increasing  their
        usefulness  and making them, so far as possible,  generally
        available to the public;
     ôc)   to harmonize the actions of nations in the attainment of
        those ends;ö

      (c)    that  Article  40 of the Convention  states  that,  in
furtherance  of  complete  international  coordination  on  matters
affecting   telecommunication,  the  Union  shall  cooperate   with
international   organizations   having   related   interests    and
activities;

      (d)   that in the study of data transmission the CCITT has to
collaborate with the organizations dealing with data processing and
office  equipment  and particularly the International  Organization
for  Standardization  (ISO) and the International  Electrotechnical
Commission (IEC);

      (e)   that this collaboration has to be organized in a manner
that  will  avoid duplication of work and decisions that  would  be
contrary to the principles set out above;

unanimously declares the view

      that international standards for data transmission should  be
established with the following considerations in mind:

      (1)    Clearly it will be the responsibility of the CCITT  to
lay  down standards for transmission channels, i.e. aspects of data
transmission   which  require  a  knowledge  of   telecommunication
networks or affect performance of these networks.

      (2)    The  standardization  of  signal  conversion  terminal
equipment   (modems)   is   the  province   of   the   CCITT;   the
standardization of the junction (interface) between modem  and  the
data  terminal equipment is a matter of agreement between the CCITT
and the ISO or the IEC.

      (3)   Devices designed to detect and (or) correct errors must
take account of:
     ù  the error rate tolerable to the user;
     ù  the line transmission conditions;
     ù  the  code,  which has to meet the exigencies  of  the  data
        alphabet  and the requirements of error control (this  must
        be  such  as  to give an output satisfactory to  the  user)
        together   with   the  requisite  signalling  (synchronism,
        repetition signals, etc.).

      Standardization here may not come wholly within  the  CCITT's
province, but the CCITT has very considerable interests at stake.

      (4)    The alphabet (as defined in Fascicle XI.1 ù Terms  and
Definitions) is a ôtable of correspondence between an agreed set of
characters and the signals which represent themö.

      The  CCITT  and the ISO reached agreement on an alphabet  for
general  (but  not exclusive) use for data and message transmission
and  have  standardized  a  common  alphabet  which  is  known   as
International  Alphabet No. 5 (CCITT Recommendation  T.50  and  ISO
Standard   No.  646ù1983;  ISO  7ùbit  coded  character   set   for
information interchange).

     Complementary study of some control characters of the alphabet
should be effected cooperatively.

      (5)    Coding  (as  defined  in Fascicle  XI.1  ù  Terms  and
Definitions)  is  ôa system of rules and conventions  according  to
which  the telegraph signals forming a message or the data  signals
forming  a  block  should  be  formed,  transmitted,  received  and
processedö. Hence, it consists of a transformation of the format of
the  signals  in  the  alphabet for taking account  of  synchronous
methods,  and  introduction of redundancy in  accordance  with  the
error  control system. This is not a field in which the CCITT alone
may be able to decide; however, no decision should be taken without
reference  to  the Committee, because of the possible  restrictions
which  transmission  and  switching  peculiarities  may  impose  on
coding.

     When the general switched network is used (telephone or telex)
and  when  the  error control devices are subject  to  restrictions
(switching signals ù reserved sequences), it is the CCITT which  is
in   fact   responsible  for  any  necessary   standardization   in
conjunction with other bodies.

      (6)    The limits to be observed for transmission performance
on   the  transmission  path  (modem  included)  fall  within   the
competence   of   the  CCITT;  the  limits  for  the   transmission
performance  of  the sending equipment and the margin  of  terminal
data  equipment  (depending  on  the  terminal  apparatus  and  the
transmission path limits) should be fixed by agreement between  the
ISO and the CCITT.

      (7)    In all instances, the CCITT alone can lay down  manual
and  automatic operating procedures for the settingùup, holding and
clearing of calls for data communications when the general switched
networks  are  used,  including type and  form  of  signals  to  be
interchanged  at the interface between data terminal equipment  and
data circuit terminating equipment.

      (8)    When a public data network is involved, the CCITT  has
the  responsibility  to  provide the Recommendations  which  apply.
Where these Recommendations have an impact on the basic design  and
features  of data processing systems and office equipment [normally
the  Data  Terminal Equipment (DTE)], they shall be the subject  of
consultation  between  CCITT and ISO and in  some  cases  a  mutual
agreement may be desirable. Likewise when the ISO is developing  or
changing  standards that may affect compatibility with  the  public
data network there shall be consultation with the CCITT.