ConTEL 2003: Tutorial T6

Date: Friday, June 13, 2003, 11:00-13:00
Location: Faculty of Electrical Engineering and Computing
Duration: 2 hours (no coffee-breaks)
Registration fee: 75 EUR

ABSTRACT

The increasing demand for network capacity & flexibility has led to the use of wavelength division multiplexing in point-to-point systems and the development of the optical cross-connects necessary to deploy (in the near future) a dynamically reconfigurable optical transport network based on wavelength routing. As network traffic has become dominated by data (IP in particular) it is necessary to ensure that the networking technology is suitable for bursty traffic sources to ensure good channel utilisation. For these reasons optical burst and traffic switching are being studied to provide both flexibility and efficient use of the wavelength channel. Such technologies can evolve from the dynamically reconfigurable network [often called the Automatic Switched Optical Netwok-ASON]
Optical burst switching is considered the nearer term technology as it arguably places less demanding requirements on buffers and switches. Switch resources are pre-assigned by a control packet, and the data burst can cut-through the switch without the need for extensive buffering.
Optical packet switching [OPS] operates in a store-and-forward manner, with a header attached to the data payload. The node design requires fast (ns) switching and techniques for overcoming optical packet contention A key issue in OPS is whether to use synchronous or asynchronous transmission; the latter enables the use of variable length packets providing a close analogy to electronic IP packets. Asynchronous operation removes the requirement for synchronisers at the switch input, which can be costly to implement, however it is more demanding in terms of buffer control and utilisation.
The implementation of OPS requires a packet labelling technique suitable to optical systems. Various schemes have been proposed and demonstrated, most of an opto-electronic nature, ie use optical detection and electronic processing rather than all optical processing. For example many successful demonstrations have used sub-carrier multiplexing, where the header is formed by modulating the header data on to a sub-carrier placed outside the data spectrum; the header data may be at a lower bit-rate than that of the payload. This method allows for easy header detection . More recently optical label processing techniques based on fibre bragg gratings have been successfully demonstrated.
The optical packet switch must incorporate a number of functions, for example, label swapping, contention resolution and payload switching are key requirements; together with appropriate algorithms for scheduling packets through the switch. The way in which these functions are implemented is related to the choice of packet format. For example a common approach to realising a large space switch fabric is through the use of wavelength conversion followed by wavelength selection. Incoming payloads are converted to a wavelength which will route the packet to the appropriate output port. This technique also facilitates the realisation of contention resolution, where a contenting packet can be diverted to an optical delay line (for buffering) by appropriate setting of the wavelength converter.
In recent years many tesbeds have been implemented [in Europe and USA] to illustrate how OPS might be realised. The presentation will conclude by giving a review of the major projects and outcomes.

OUTLINE OF THE TUTORIAL

Network scenarios
Traffic profiles
Optical burst switching
Optical packet switching
Packet formats
Labelling techniques
Node functions
Switch fabrics
Label swapping
Testbeds & experiments
Summary

AUTHOR

Mike J O' Mahony received his Ph.D degree in 1977, from the University of Essex, England for research into digital transmission systems.
In 1979 he joined the Optical System Research Division of British Telecom working on research into fibre-optic systems for undersea systems; in particular experimental and theoretical studies of receiver and transmitter design. In 1984 he became a Group Leader responsible for the study and application of optical amplifiers to transmission systems. In 1988 he became a Head of Section responsible for 50 graduates researching terrestrial long haul optical systems and networks. Areas of interest included optical amplifiers, coherent optics, pico-second pulse systems and optical networks. In 1991 he joined the Department of Electronic Systems Engineering at the University of Essex as Professor of Communication Networks. He was Head of Department from 1996-1999.
Current research is related to the study of future network infrastructures and technologies, in particular optical packet switching. He is principal investigator for grants supported by industry, national research councils and the EU.
Professor O' Mahony is the author of over 250 papers relating to optical communications, is a member of the IEE and a senior member of the IEEE.

[ back to Tutorials ] [ previous ]

contact