Abstract: A telephone switch in which communication between tasks controlling the switch hardware and the timing of those tasks, including the timing of repeating tasks, is controlled through a mail system in which mail messages are sent between tasks that may be running on separate microprocessors. The mail messages specify the destination task, the function that the task is to perform and any desired delay before the mail is to be delivered to the destination task. Repeating tasks send mail to themselves each time they repeat, specifying in the mail message the task to be repeated and the desired delay interval. A mail task holds the mail for the specified delay interval before it is delivered, and receipt of a mail message causes the task to run.

Abstract: A channel allocation system for selecting the earliest available switch port and time division multiplexed channel for an outgoing transmission in a network of switch elements interconnected by a series of communications paths. An availability table for maintaining the free/busy state of each channel on each switch port in the switch element is provided. Means are additionally provided for limiting the search of the availability table for the earliest available channel to certain desired switch ports and channels.

Abstract: A conferencing device and method among terminals in a distributed digital telephone switching system is provided. The telephone switching system has a plurality of switching elements for interconnecting telephone units and telephone lines via communication links. A duplex path is set between each party in the conference and a designated bridge port. The speech from all the parties in the conference is summed and at the bridge port the sum is sent back to all engaged in the conference. As each party receives the sum, it subtracts its own speech data and therefore obtains the speech data from the other parties in the conference.

Abstract: A communication switching system with distributed control processing is provided. The system includes a digital switching network having a modular array of intelligent digital switching elements each having processors and memory to set up communication paths for voice and data between the terminal module processors such as line cards and telephone units. Each addressable location in the system is assigned a logical address code (LAC). When a route is requested, a switch element processor interprets the destination LAC and selects a route through the switch toward the destination with each switch element in the communication path setting a route toward that destination. The switching network provides duplex paths for flexible communication. With such a duplex path speech is directed from a first terminal unit such as a telephone station and a second terminal unit such as a line card into a bridge port which sums the speech data from the two sources.