Recommendation B.171) 
                             ADOPTION OF THE CCITT SPECIFICATION AND DESCRIPTION
                                               LANGUAGE (SDL)
               The CCITT,
         considering
               (a) that there is  a  need  for  a  common  method  or  procedure  for  the
         unambiguous specification and description of the behaviour  of  telecommunication
         systems;
               (b) that a specification of a system is the  description  of  its  required
         behaviour;
               (c) that a description of  a  system  is  the  description  of  its  actual
         behaviour;
               (d) that a universal method for specification and description should  bring
         economic benefits;
               (e) that the CCITT has adopted such a method called the  Specification  and
         Description Language (SDL) as described in CCITT Recommendations Z.100 to Z.104,
         recommends
               (1) the adoption within the ITU of the use of the CCITT  Specification  and
         Description Languae  (SDL)  for  unambiguous  specification  and  description  of
         telecommunication systems (see Annex A);
               (2) that the possibilities for  application  of  SDL  in  areas  of  common
         interest for the purposes of standardization be brought to the attention of other
         international bodies (e.g. the IEC and ISO) for their consideration.
                                                   ANNEX A
                                      (to Recommendation B.17)
                                        Introduction to SDL
               The purpose of recommending SDL is to provide a  language  for  unambiguous
         specification and description of the behaviour of telecommunications systems. The
         specifications and descriptions using SDL are intended to be formal in the  sense
         that it is possible to analyse and interpret them unambiguously.
               The terms  specification  and  description  are  used  with  the  following
         meaning:
               -   a specification of  a  system  is  the  description  of  its  required
                  behaviour, and
               -   a description of a system is the description of its actual behaviour.
               SDL  also  provides  structuring  concepts  which  allow  a  system  to  be
         partitioned so that it can be defined, developed and understood  one  part  at  a
         time.
               These concepts are of value both initially in  specifying  a  system,  when
         different aspects can be independently dealt with,  and  later  in  describing  a
         system, when the description structures should match the system structure.
         SDL 
         SDL semantics, they are equivalent from a semantic point of view.
               Objectives
               The general objectives when defining SDL have been to  provide  a  language
         that:
               -   is easy to learn, use and interpret in relation to  the  needs  of  an
                  operating organization;
               -   provides unambiguous specifications and descriptions for ordering  and
                  tendering;
               -   may be extended to cover new developments;
               -   is able to support several methodologies of system  specification  and
                  design, without assuming any one of these.
               Scope
               The main are of application for SDL is the description of the behaviour  of
         aspects of telecommunications systems. Applications include:
               -   call processing (e.g. call handling, telephony signalling, metering) in 
                  stored programme control (SPC) switching systems;
               -    maintenance  and  fault  treatment  (e.g.  alarms,  automatic   fault
                  clearance, routine tests) in general telecommunications systems;
               -   system control (e.g.  overload  control,  modification  and  extension
                  procedures);
               -   data communication protocols.
               SDL can of course also  be  used  for  the  description  of  any  behaviour

         1)      A similar text will be submitted to the CCIR as revision of Recommendation 664.



         Fascicle I.3 - Rec. B.17                  PAGE1

         capable of being described using a discrete model, i.e.  communicating  with  its
         environment by discrete messages.
               A description of SDL is given in CCITT Recommendations Z.100 to Z.104.


































































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