Telecommunication exchange

摘要

In a small business-type telephone exchange, calls are set up in TDM manner using PCM to convey speech and data if the exchange serves any data terminals. The exchange has subscriber line ports (SLC) each serving two lines and a smaller number of trunk line ports (TLC) each serving a trunk to a local exchange. Each port has a local processor (SIP) with analogue-digital and digital to analogue conversion circuitry (CODEC-FILTER-TSAC). The exchange also has a central processor (CCP) with its associated memories (ROM, RAM, EAROM). The ports and the central processor are interconnected by an intelligence bus (PCM BUS) and a signalling bus (SIG BUS). The central processor (CCP) and the port processors (SIP) co-operate in call setting with all communications between the processors over the signalling bus. During operation the central processor (CCP) polls the ports via the signalling bus (SIG BUS) for ports needing the services of the central processor and also to pass call control information to those ports. To set up a call between the lines, or a line and a trunk, two time slots in the TDM cycle are allocated to the call by the central processor, one for each direction of transmission. The intelligence bus (PCM bus) is thus used only to convey intelligence, i.e. speech and/or data and tones.