Both Local and Transit Exchange
 
 At lower levels in the hierarchy, the transit task is often combined with that of
  serving a subscriber area. In addition to the system core above, such exchanges
  require all services we found in the local exchange. The following functions are
  thus to be found in a combined local and transit exchange.....

    Subscriber Stage
    Subscriber Services
    Trunk and Signaling Stage
    Group Switch
    Control
    Operation and Maintenance
    Charging

  The charging function is used for charging the calls of the connected subscribers,
  but also for the charging of the traffic which is switched between the lower order
  exchanges.
 
 
 
 

 
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