Department of Computer Science and Technology

Technical reports

Reconfigurable wavelength-switched optical networks for the Internet core

Tim Granger

November 2003, 184 pages

This technical report is based on a dissertation submitted August 2003 by the author for the degree of Doctor of Philosophy to the University of Cambridge, King’s College.

Some figures in this document are best viewed in colour. If you received a black-and-white copy, please consult the online version if necessary.

DOI: 10.48456/tr-575


With the quantity of data traffic carried on the Internet doubling each year, there is no let up in the demand for ever increasing network capacity. Optical fibres have a theoretical capacity of many tens of terabits per second. Currently six terabits per second has been achieved using Dense Wavelength Division Multiplexing: multiple signals at different wavelengths carried on the same fibre.

This large available bandwidth moves the performance bottlenecks to the processing required at each network node to receive, buffer, route, and transmit each individual packet. For the last 10 years the speed of the electronic routers has been, in relative terms, increasing slower than optical capacity. The space required and power consumed by these routers is also becoming a significant limitation.

One solution examined in this dissertation is to create a virtual topology in the optical layer by using all-optical switches to create lightpaths across the network. In this way nodes that are not directly connected can appear to be a single virtual hop away, and no per-packet processing is required at the intermediate nodes. With advances in optical switches it is now possible for the network to reconfigure lightpaths dynamically. This allows the network to share the resources available between the different traffic streams flowing across the network, and track changes in traffic volumes by allocating bandwidth on demand.

This solution is inherently a circuit-switched approach, but taken into account are characteristics of optical switching, in particular waveband switching (where we switch a contiguous range of wavelengths as a single unit) and latency required to achieve non disruptive switching.

This dissertation quantifies the potential gain from such a system and how that gain is related to the frequency of reconfiguration. It outlines possible network architectures which allow reconfiguration and, through simulation, measures the performance of these architectures. It then discusses the possible interactions between a reconfiguring optical layer and higher-level network layers.

This dissertation argues that the optical layer should be distinct from higher network layers, maintaining stable full-mesh connectivity, and dynamically reconfiguring the sizes and physical routes of the virtual paths to take advantage of changing traffic levels.

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BibTeX record

  author =	 {Granger, Tim},
  title = 	 {{Reconfigurable wavelength-switched optical networks for
         	   the Internet core}},
  year = 	 2003,
  month = 	 nov,
  url = 	 {},
  institution =  {University of Cambridge, Computer Laboratory},
  doi = 	 {10.48456/tr-575},
  number = 	 {UCAM-CL-TR-575}