Draft Recommendation O.ax(0.1)


       SCOPE AND APPLICATION OF 0-SERIES RECOMMENDATIONS

1.     Scope of O-Series Recommendations

       The CCITT makes various Recommendations covering:

       a)   essential specification clauses  for  telecommunications
            equipments, and 

       b)   operational matters e.g. procedures for bringing  circuits  into
            service and routine checks of performance.

       The character of the tests for checking  compliance  with  these  two
categories of Recommendation are essentially different, and this often leads to 
a different choice of test equipment.

       Category a) tests will normally be more comprehensive. Their  purpose
(often based upon measurements of sample  or  prototype  equipments)  is  to
certify compliance with design objectives and they may therefore be a precursor to 
equipment being accepted for installation in  an  administration's  network.
Such tests are unlikely to be employed routinely and in general CCITT does not 
produce Recommendations for test equipment intended  specifically  for  this
purpose.

       Category b) tests, however, are used systematically and  repetitively
and their widespread application may necessitate additional  considerations,
in particular the need for;

       1)   conformity of results when tests may  be  performed  using  test
            equipment supplied by more than one manufacturer, and;

       2)   a common measurement technique to ensure  compatibility  when  a
            test requires test equipment at both ends  of  an  international
            circuit.

       It is primarily for these circumstances that CCITT issues  the  O-Series
Recommendations.

       The above remarks apply equally to analogue and digital techniques.

2.     Application of measuring  equipment  for  use  on  digital  transmission
       systems

       This  section  is  presented  as  an  aid  to  selecting  and   applying
specifications in the O-Series of Recommendations concerning tests and measuring equipment 
for use on primary PCM and data multiplexers and digital transmission systems.

       Applications are divided into two categories:

       i)   measurements and indications on primary PCM multiplexers;

       ii)   measurements  and  indications  on  digital  transmission  systems
            including digital line systems, digital circuits and digital multiplexers.

       Figure 1/O.ax and  Figure  2/O.ax  illustrate  the  range  of  test  and
measurement capabilities applicable to primary PCM multiplexers, in the send and 











receive directions respectively.

       Figure 3/O.ax and  Figure  4/O.ax  illustrate  the  range  of  test  and
measurement capabilities applicable to digital transmission systems.

       The figures indicate the relevant O-Series Recommendations to be applied 
for each test and measurement parameter, and also show the connection interface 
for the test instrument.

For example:

       To measure quantizing distortion on a primary PCM multiplexer.

       Figure 1/O.ax shows that instruments conforming to Recommendations O.131 
and O.132 can be employed, connected to the audio input interface of  the  send
encoder.

       Figure 2/O.ax shows that similar instruments are connected to the  audio
output interface of the receive decoder to complete the measurement path.

3.     Application of measuring equipment  for  use  on  analogue  transmission
       systems

       Under study.