Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Patent
1994-06-15
1996-01-30
Boudreau, Leo H.
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
359140, H04J 1408
Patent
active
054885019
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to an optical processing system, and in particular to optical header recognition in packet switching networks.
In a circuit switched telecommunications network, a physical circuit is made between two terminals for the duration of a call. For certain traffic formats, such as speech, the information being transmitted never completely fills the connection between two terminals, that is to say the start of the information does not reach the destination terminal before the end of that information leaves the transmitting terminals, but the circuit is held open for the duration of the information's transmission between the two terminals. With high-speed circuits carrying digital data, a much greater resource utilisation is possible by sharing paths through the network. A packet switching network is one way of achieving this improved resource utilisation, data being transferred through the network in packets. Each packet includes, apart from the data itself, a header containing addressing and sequence (control) information for controlling the progress of that packet through the network. The addressing and sequence information coded in the header of a packet is decoded at the network nodes to provide routing control. A packet switching network thus provides a virtual circuit between two terminals, this circuit appearing to the users as a permanent connection between the terminals but which, in fact, is shared with other users.
BACKGROUND OF THE INVENTION
Known methods of coding packet headers rely on time correlation techniques. The utilisation of a packet switching network is linked to the bit-rate. The utilisation also depends upon the ratio of data time to wasted time, that is to say the ratio of the time the network is transmitting data to the time data is not being transmitted. In the time domain, the wasted time is made up of the time taken up with header transmission (the header of a packet occupying a separate time slot at the head of the data of that packet), and by the guard band transmission time, the guard band being the separation between adjacent packets which is essential to avoid overlap of the packets due to dispersion during transmission.
BRIEF DESCRIPTION OF THE INVENTION
The aim of the invention is to provide an alternative technique for coding and decoding header information, particularly in packet switching networks, which technique results in increased network utilisation.
The present invention provides a telecommunications system comprising first and second nodes interconnected by a network transmission line, the first node comprising an optical data generator for producing an optical data signal at a first wavelength, an optical header generator for producing an optical control (header) signal at a second wavelength, means for multiplexing the data and control signals onto the transmission line in such a manner that the duration of the control signal is at least equal to the duration of the data signal, a delay unit and control means associated with the delay unit for providing a sufficient delay between the transmission start times of the control and data signals to ensure that the control signal completely overlaps the data signal on arrival at the second node, the second node comprising a switch and a controller responsive to signals at the second wavelength for controlling the routing of optical signals through the switch.
As the control signal overlaps the data signal, the two signals occupy the same time slot.
Advantageously, the optical data generator produces optical data signals in packets, and preferably the optical data generator is constituted by a laser and a modulator for modulating the output of the laser. The header generator may also be constituted by a laser.
The system may further comprise a modulator for modulating the header laser so as to turn the header laser on at, or just before, the start of a data packet and to turn the header laser off at, or just after, the end of a data packet.
Conveniently, the controller of
REFERENCES:
patent: 4831616 (1989-05-01), Huber
Barnsley et al., "Wavelength Conversion from 1.3 to 1.55 .mu.m Using Split contact Optical Amplifiers", IEEE Photonics Technology Letters, vol. 3, No. 3, 1 Mar. 1991, New York US, pp. 256-258.
Yamaguchi et al., "A Broadband Access Network Based on Optical Signal Processing: the Photonic Highway", Proceedings IEEE Infocom 1990, 3 Jun. 1990, San Drancisco (US), pp. 1030-1037.
Boudreau Leo H.
British Telecommunications PLC
Negash Kinfe-Michael
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