Multiplex communications – Wide area network – Packet switching
Patent
1993-11-23
1995-11-21
Olms, Douglas W.
Multiplex communications
Wide area network
Packet switching
370 953, 3701051, H04J 316
Patent
active
054694400
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to communications networks and particularly but not exclusively to networks known in the art at TPON networks. TPON is an acronym for Telephony over Passive Optical Network.
2. Related Art
A TPON network has been developed by the assignee of the present application and is described in the article "The provision of telephony over passive optical networks" by Hoppitt, C. E. and Clarke, D. E. A., British Telecom Technology Journal, Vol. 7, No. 2, pp 101-114 April, 1989. The signals from the different outstations, or network terminations, are bit-interleaved in the upstream multiframe, and correspondingly in the downstream multiframe. The outstations have separate transmitters and receivers, and thus it is possible for an outstation to transmit traffic signals at allocated channels in the upstream multiframes at the same time that it receives signals from the downstream multiframes.
In such a TPON network it would not be a simple matter to employ a transceiver, i.e. a single transducer for both functions, in an outstation. The central station, or head-end, would need to compute for each bit transmitted to each outstation which bits in the upstream multiframe would correspond to a transmit/receive conflict, i.e. that (a) the outstation was required to transmit at the same time as it was receiving, or (b) that the outstation was required to receive a bit before recovering from transmission of a bit to the central station. The allocations of the bit positions in the downstream and upstream multiframes for communications between the central station and an outstation would be determined by the results of the respective computation by the central station.
BRIEF SUMMARY OF THE INVENTION
According to a first aspect of the present invention there is provided a method of communicating via a communications network comprising a central station, a plurality of outstations, and a transmission medium in the form of a branch arrangement between the central station and the outstations, the method comprising transmitting from the central station multiplexed signals for the outstations in the form of a stream of broadcast frames, transmitting from the outstations return signals for the central station in the form of a stream of return frames in which the return signals are passively multiplexed, characterised in that each broadcast frame comprises a control portion and a traffic portion, the control portion comprises a series of contiguous first subframes each containing control information for a respective outstation, and the traffic portion comprising a series of contiguous second subframes each containing multiplexed respective blocks of traffic information for the outstations, and in that in at least one of the outstations the return signals are transmitted using the same transducer that is used for receiving the broadcast frames.
The abovementioned difficulty of employing a transceiver with the bit-interleaved frame format of the above article is alleviated by providing the respective control words in respective contiguous first subframes, and providing the traffic information for respective outstations in respective blocks in each second subframe. This increases the maximum operating range of the network beyond which the transmit/receive conflict occurs, and the central station does not have to do any computations to find out if there are any channel positions in the second subframes which it cannot allocate to a communication with a particular outstation because of a transmit/receive conflict.
Preferably, each of said respective blocks of traffic information is a group of contiguous signal bits.
Preferably, each broadcast frame comprises a respective non-operational portion following the control and traffic portions and in which no control or traffic information signals are transmitted.
Preferably, each broadcast frame comprises a synchronization and ranging portion following one of the non-operational portions.
Preferably, this synchronizati
REFERENCES:
patent: 4847833 (1989-07-01), Doering et al.
patent: 5081704 (1992-01-01), Umeda et al.
patent: 5341365 (1994-08-01), Clarke
Hoppitt et al, "The Provision of Telephony Over Passive Optical Network", British Telecom Technology Journal, vol. 7, No. 2, pp. 101-114.
British Telecommunications
Olms Douglas W.
Ton Dang
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