THE DTX-240D DIGITAL CIRCUIT MULTIPLICATION SYSTEM

This paper describes the DTX-240D digital circuit multiplication system (DCMS) offered by ECI Telecom. It will accept up to 240 x 64 kb/s trunks carrying either 64 kb/s voice, voice band analogue non-speech signals, or digital data for transmission over a 2.048 Mb/s digital link. Over 1000 are currently 'on-line' and carrying traffic. The system comprises a pair of terminals, one on each side of the interterminal digital link (bearer). It will normally operate in the network at a concentration ratio of 5:1, in which case 150 x 64 kb/s trunks, carrying voice, voice band data or digital data can be concentrated into one 2.048 Mb/s bearer. The users are able to increase the number of trunks up to 240 per 2.048 Mb/s bearer, when time zone differences cause a spread of busy-hour traffic carried on a single system. Each terminal will normally be located at an international switching centre (ISC) but may also be located at an earth-station. The system uses a DSI (digital speech interpolation) stage providing a 2.5:1 multiplication, followed by an additional 2:1 multiplication by means of ADPCM (adaptive differential pulse code modulation). In addition, the VBR (variable bit rate) technique is used to prevent clipping, due to overload congestion. The system can also be used with 1.544 Mb/s digital bit streams (trunk side or bearer).