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Mismatch in coin collection and Exchange Meter Reading for CBT-95 PCOs

       It has been reported from the field that when a call is originated from a CBT-95 Coin Collection Box (CCB) after inserting a one rupee coin, the meter reading, for a call continued for 90 seconds, is incremented by two while only one coin is collected. This leads to mismatch between the collection from the ccb-pco and its meter reading. The problem can be solved by simple data modifications. A description of the problem, and the remedial measure, are explained below:
       In C-DOT exchanges, the charging for CCB-PCO is governed by the following two system parameters: 1. PCO-MTR-LCL and 2. CCb-CL-CNVRS
      The value of the PCO-MTR-LCL is the charge rate number according to which the charging is done for the local calls originated from the pco. Value of the other parameter CCB-CL-CNVRS gives the duration of the call allowed from the CCB-PCO. For example , let the values of PCO-MTR-LCL be assigned as ‘7’ , the charge rate number , which signifies a pulse 90 seconds, and the CCB-CL-CNVRS as 3600. these settings will permit a maximum 360 seconds or (6 minutes) call where meter reading increments every 90 seconds.
        Now , in CBT-95 , there is a built-in timer of 90 seconds. An indication (tone/display) is also given after 70 or 80 seconds to request the user to insert another coin if the call is to be continued beyond 90 seconds. Because of a race condition in the CBT-95, a situation may arise where exchange’s 90 seconds elapse before CPT-95’s 90 seconds. The exchange meter increments by 1 after expiry its 90 seconds and again by 1 when CBT-95 disconnects the call after the expiry of its 90 seconds. Thus meter reading increments by 2 while only one coin has been collected by the CCB.
        This problem can be solved by assigning a charge rate number with pulse rate of 91 seconds (or modify the existing charge rate number) in PCO-MTR-LCL. This way, the exchange call will not time out before the CBT-95 timer and the meter reding of the coin-collection will match.

Reference: Issue 59 of Telematics from C-DOT