Abstract: The Integrated Services Digital Network ("ISDN") normally uses 64 Kbits/sec channels which are therefore unsuitable for data traffic at higher rate traffic. This can be overcome by assembling ISDN channels to form higher bit rate channels. However, when the bit-rate required changes frequently, the number of channels grouped together must be changed often. To solve this problem, data packets are received from local area networks by a computer and assembled into groups of ISDN channels which are combined to form high bit rate channels or U-channels. The computer assembles data into an ISDN frame using an appropriate number of slots in the frame for each U-channel. The frames are transmitted using conventional ISDN circuits. On reception, ISDN slots in frames are passed to packet assembly buffers, one for each U-channel, before being passed to users. When a new slot is to be added to a U-channel, synchronization signals are sent in the new slot and flags are used to establish when data is to be sent.

Abstract: Digital data networks (such as the ISDN) which provide transmission between selected locations may use time multiplexed slots with predetermined maximum bit-rates. However local area networks (LANs) transmit packets, containing data bits, at a rate which varies frequently and often corresponds to a higher bit-rate than can be handled by individual slots. In the present invention packets arriving at an input port are allocated to a number of queues each for a respective destination, and each queue is allocated a group of slots on a digital data network. The slot contents are assembled into frames in a buffer store and transmitted to the digital network. On reception, the contents of several frames of incoming multiplexed slots are held in a frame store and then assembled into packets in a number of buffers making allowance for arrival in a different slot order and different frames.