Random access protocol for multi-media networks

A protocol for mixed voice and data access to a synchronous broadcast communications channel is provided. Transmission on the broadcast communications channel is by means of a plurality of time division frames, each such frame being defined by a plurality of time slots. The protocol requires that a user determine whether a time slot is available. If a slot is available, a user transmits a preamble on the broadcast communications channel and then substantially simultaneously monitors the channel for determining whether a collision of the preamble has occurred. If a collision has occurred with a second user who has a higher priority, the first user reattempts to acquire an available time slot after a time delay, the time delay being equivalent to a random number of time slots. If on the other hand, the collision was with a second user of equal priority, both users will reattempt acquisition of available time slots after respective random time delays. The preambles of users of different priority are transmitted using a non-interfering code or modulation frequency, thereby allowing the higher priority user to continue transmission of the remaining fields which make up that user's information packet. Another key feature of the protocol is the use of the preamble to identify voice users that are in silence periods, transmitting no data. Under these circumstances, the protocol permits data users to utilize such identified time slots when they are encountered, thereby increasing the throughput of the data communications system.

Patent #: 5453987 Issue Date: September 26, 1995