GB1303270A - - Google Patents

Abstract

1303270 Digital transmission; multiplexing systems STANDARD TELEPHONES & CABLES Ltd 25 Aug 1971 [2 Sept 1970] 41988/70 Heading H4P A multiplex digital data switching centre for multiple mixed channels operating at different speeds in which storage areas are grouped within a single store with suitable access means comprises a plurality of channels operating at each speed, the centre having a plurality of data storage devices one for each channel with all the devices associated with each speed being grouped together. The incoming characters are scanned and a means for associating the scanning time of each character with a corresponding channel address in the storage devices is provided together with means for transferring the characters to the devices associated with the addresses. In a preferred embodiment the centre has a plurality of counters one for each speed which are incremented when a character at appropriate speed is scanned, the means for transferring being operated to transfer characters to the appropriate storage devices which are indicated by the counter content. Incoming channels may be bit or envelope interleaved. Assuming that a system is based on a number of basic 12 Kb/s channels in the 12 Kb/s frame with 10 bit envelope interleaving, the scan time is 20À8 Ás per envelope. The address corresponding to an incoming channel is derived by adding the base address indicating the start of a storage area corresponding to the particular channel x, y or z to the frame base address n.2<SP>M</SP> where n is a number of 12 Kb/s unirate multiplexed channels and M is a number of binary digits in the address specifying the channel within a frame, plus the address of the information channel within its own 12 Kb/s frame (m). A table giving the channel rates and corresponding forms of addresses is given in a Specification. The frame base address can be made available by permanently storing the address and extracting it concurrently with the transfer of characters on the corresponding 12 Kb/s channel. The address has the form n.2<SP>M</SP> so it is only necessary to store n providing other means available for defining the channel rate. Alternatively each channel is scanned and accessed once in each major period with the order of access within a major scan constant. With a bit interleaving the method is identical. Incoming frames may be completely aligned with outgoing frames or completely aligned with each other but not the outgoing frames. Since we have a phase difference this requires a buffer storage of say four envelopes which if set at a determined figure so that the positional change is known, a common frame address counter can be used but the delay factor slightly complicates the address formation.