Multiplex communications – Wide area network – Packet switching
Patent
1992-05-22
1994-01-11
Chin, Wellington
Multiplex communications
Wide area network
Packet switching
370 942, 370112, H04J 322
Patent
active
052788270
ABSTRACT:
Communication channels provided by the Integrated services Digital Network (ISDN) usually carry 64 Kbits/sec in each direction and are therefore unsuitable for data traffic at higher rates. This difficulty can be overcome by assembling ISDN channels to form channels having a higher bit rate. However problems arise, for example, in the transmission of data packets where the bit-rate required changes frequently and therefore the number of channels grouped together must be changed often. These problems are tackled as now described. Data from different data streams to be transmitted is read into respective buffers in a RAM. ISDN channels are grouped into channels known as slots and U-channels, respectively, and each U-channel transmits a respective data stream. Data from the buffers are assembled into frames, corresponding to an ISDN frame in a frame store by a microprocessor. Information controlling how the data is assembled in the frame store is held by a slot control RAM and respective control portions of the RAM. Conventional ISDN circuits take frames from the store for transmission and fill a receive frame store on reception from other stations in the ISDN. The RAM takes account of any "skew" due to differential delays in different ISDN channels in reading out from the frame store into receive buffers. When a U-channel is to be expanded, without interruption of the existing slots in the U-channel, by the addition of another slot, a first distinctive synchronizing packet is transmitted which indicates the U-channel to which the new slot is to belong. When this packet has been acknowledged a second distinctive synchronizing packet is transmitted which carries a time reference for calculating skew and then data is sent in the new slot in the next frame. When the bit-rate for a U-channel falls one of the slots of that U-channel can be closed by transmitting a distinctive closing packet in that slot. On reception of this packet that slot is deleted in the next frame.
REFERENCES:
patent: 4553250 (1985-11-01), Bryant
patent: 4577312 (1986-03-01), Nash
patent: 4759017 (1988-07-01), Allan et al.
patent: 4763319 (1988-08-01), Rozenblit
patent: 4775987 (1988-10-01), Miller
patent: 4805167 (1989-02-01), Leslie et al.
British Technology Group Ltd.
Chin Wellington
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