Voice traffic capacity of a distributed PABX based on CSMA/CD LAN technology

An examination is made of the feasibility of constructing a large distributed PABX by interconnecting a number of small (128-line) multiplexers using a CSMA/CD (carrier-shift multiaccess with collision detection) local area network. The multiplexers are themselves 128-line PABX modules capable of switching locally without reference to the network. A major problem with CSMA/CD for speech transmission is the inherent packetization delay which can considerably exceed the 2-ms delay normally specified by PTT authorities for subscriber premises networks (SPNs). The multiplexers tackle this problem by distributing packetization delay over several active sources. The choice of parameters to minimize delay as a function of throughput for the distributed PABX topology is considered