Q. Important function of common control subsystem?

If a call is destined to a number in an exchange other than present one processing the digits, initial translator generates the require routing digits and passes them on to register sender. Here the digits corresponding to the subscriber identification are concatenated and combined digit pattern is transmitted over the trunks to external exchange. Register sender uses appropriate signaling technique, depending on requirements of destination exchange. If the call is destined to a subscriber within same exchange, digits are processed by final translator. Translation of directory number to equipment number occurs at this stage. Final translator determines line unit to that a call should be connected and category of the called line. Category information may influence charging and connection establishment. In a number of practical implementations, both initial and final code translator functions are performed by a single translator. Controlling operation of switching network is an important function of common control subsystem. This is done by marking switching elements at different stages in accordance with a set of binary data defining the path and then commanding actual connection of the path. Path finding may be carried out at the level of common control unit or switching network.