Transmission system

Claim 1

An information transmission system, in which digital data is conveyed in successively-occuring fixed-duration envelopes each of which provides capacity for a number of successive equal-duration bit frames, in which: (a) the system has first input means over which circuit-switched traffic is received by the system and second input means over which packet-switched traffic is received by the system, circuit-switched traffic being routed into first buffer storage means and packet-switched traffic being routed into second buffer-storage means; (b) a timing means for the system allots bit frames at the commencement of each said envelope for a present maximum number of circuit-switched communications, the remainder of that envelope being available, under the control of said timing means, for conveying packet-switched traffic, the arrangement being such that priority is given to circuit-switched traffic; (c) the duration of said envelope is such that a said envelope has a capacity greater than that needed to accommodate the maximum number of simultaneously-existing circuit-switched communications to be catered for; (d) a monitoring means under the control of the timing means monitors traffic incoming to the system over said first input means to determine how much circuit-switched traffic has to be handled; (e) a means under control of said monitoring means allocates capacity which is not needed for circuit-switched traffic to packet-switched traffic; and (f) a multiplex means under control of said monitoring means sends circuit-switched traffic from said first storage means to the system output using bit frames at the commencement of the envelope, whereafter during the remainder of the bit capacity of the envelope packet-switched traffic which is awaiting transmission is routed from the second buffer storage means to the system output.