Control Software for Virtual-Circuit Switches: Call Processing

The software architecture in this paper has evolved through a sequence of research projects at AT&T Bell Laboratories. We review the architecture and describe an experimental reimplementation. Calls from each device attached to a virtual-circuit switch are managed by a software process, called a line process; the line process translates call requests from the device into a uniform device-independent internal protocol. Host computers and trunks can have numerous lines multiplexed over a single physical link. This process-per-line architecture leads to a profusion of specialized processes, most of them idle, with very simple contexts. Previous implementations used machine-dependent code to manage the processes.