Recommendation E.426
                GENERAL GUIDE TO THE PERCENTAGE OF EFFECTIVE ATTEMPTS WHICH
                 SHOULD BE OBSERVED FOR INTERNATIONAL TELEPHONE CALLS
         1      General considerations
         1.1    The success of call attempts is fundamental to an automatic  international
         telephone service of high quality.
         1.2    The periodic observation of completion ratio1) and the  categorization  of
         failures to destination countries together with the exchange of such  information
         between countries are valuable  to  establish  and/or  maintain  a  high  service
         quality.
         1.3         call    completion    ratio     of     the     national
         network of a given country, as manifested through its international
         switching centre(s), affects the efficiency  of  operation  of  all
         countries routing traffic to that country.
         1.4   Call completion ratio  information  can  be  provided  either
         internally     in     an      SPC      international      switching
         centre or externally at the level  of  the  outgoing  international
         circuits in any international switching centre in which  access  to
         the circuits is  provided  for  the  purpose  of  establishing  the
         disposition of call attempts.
         1.5   The availability, flexibility and capacity  of  minicomputers
         provides  an  economically  attractive  method  of  obtaining  call
         completion ratio information with extreme accuracy.  This  includes
         the  observation  of  tones  when  suitable  interfaces  with   the
         minicomputer are provided.
         2      A guide to the proportion of effective call attempts
         2.1    A general guide for the expected percentage  of  effective  call  attempts
         during the mean busy hour and its two immediately adjacent hours, as observed  at
         the  originating  international  switching  exchange,  is  indicated  below.   An
         effective call attempt is defined, for this purpose, as one for which  an  answer
         is received at the originating  international  exchange.  Faults  caused  by  the
         originating international exchange shall be excluded to the extent feasible.  All
         attempts which succeed in seizing an international circuit shall be  included  in
         the results:
               a)  low level of effective call attempts: less than 30%;
               b)  medium level of effective call attempts: 30% to 60%;
               c)  high level of effective call attempts: more than 60%.
         2.2    When an originating country notes  a  downward  change  in  the  level  of
         effective call attempts towards any destination, the originating, destination  or
         transit Administrations should initiate investigations to determine and alleviate
         the underlying causes (e.g.  network  provisioning,  subscriber  behaviour).  The
         objective of this action is to avoid degradation in the level of  effective  call
         attempts.






















         1) See Recommendation E.600.



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