Multiplex communications – Wide area network – Packet switching
Patent
1986-10-17
1988-05-31
Olms, Douglas W.
Multiplex communications
Wide area network
Packet switching
370104, H04B 724, H04B 7185
Patent
active
047486210
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to a communications system, and interfaces therefor, in which a plurality of outstations use a single node as an intermediate for communications wherein said communications include at least a proportion of digital traffic in time division multiplexed form. The network may use two channels, e.g. two radio channels, both of which are used in a time-share mode.
The network comprising the outstations and the node will be called herein a "time-division multi-access", conveniently abbreviated to TDMA, system. The invention particularly relates to an interface circuit for interconnecting a TDMA system to an external station, i.e. one which is not part of the TDMA system, which station operates a plurality of channels in a time division multiplex format.
BACKGROUND AND SUMMARY OF THE INVENTION
The time division multiplex format commonly utilised in UK takes the form of a frame which provides time-slots for 30 digital channels, i.e. 30 traffic slots. In addition the frame has a slot, identified as "slot 0" for synchronisation and a "slot 16", i.e. the seventeenth in the sequence, which is used for signalling (that is indicating the start and end of calls and identifying numbers called to the exchange). Thus there are 32 slots in each frame.
It is also an accepted practice for a public "common carrier" of telecommunications to connect suitable customers to the public switched network via a multiplexed channel using the standard 32 slots even when the customer does not need the 30 channels provided by 30 slots. In those circumstances the operation is controlled so that only assigned slots are used.
The interface according to the invention is capable of operating with a wide range of external stations and, in particular, it is adaptable to whatever proportion of the multiplex frame is assigned to a particular external station.
A preferred interface means provides three functions; thus it comprises: multiplex format and providing said signals to a TDMA; assigned time division multiplex format; and said TDMA circuitry being operatively connected to items (a) and (b) above to provide synchronisation and compatability between the signals in said channels and the TDMA.
The first channel conveniently comprises gate-means for selecting defined slots from received frames, buffer means for storing said selected slots and burst forming means for concatenating TDMA information with the stored slots to produce a burst. The gate-means preferably comprises a frame-counter responsive to the sync slot in each frame of a received multiplexed signal wherein said frame-counter is operatively connected to a frame map store and a buffer input gate and a channel map store in such a manner that the frame-counter activates the buffer input gate to permit the passage of a byte when its count matches a value retained in the channel map store.
The duplex channel conveniently includes a reception buffer for storing received bursts, an output buffer for storing regenerated frames and frame regeneration means for transferring bytes from the reception buffer to the output buffer and for incorporating blank slots in accordance with synchronisation markers contained in said received bursts to reconstitute the specified frames.
Preferably the duplex channel also includes a slot control counter operatively linked to the channel map store to control a frame gate to pass either bytes from the reception buffer to the output buffer or to pass blank slots to the output buffer and a synchronisation detector for synchronising the count of the slot control counter with synchronisation bytes provided by the reception buffer wherein said synchronisation detector is responsive to output of the frame gate.
The TDMA circuitry conforms to the requirements of the TDMA system. In particular the interface circuitry of this invention is compatible with the TDMA system disclosed in our earlier patent application as follows:
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Ballance John W.
Edwards Steven J.
British Telecommunications public limited company
Marcelo Melvin
Olms Douglas W.
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