Optical burst switching
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Optical burst switching (OBS) is a telecommunication technique that allows dynamic sub-wavelength switching of data. Optical Burst Switching is viewed as a compromise between the yet unfeasible full optical packet switching (OPS) and the mostly static optical circuit switching (OCS). It differs from these paradigms because OBS control information is sent separately in a reserved optical channel and in advance of the data payload (or packets, now called bursts). These control signals can then be processed electronically to allow the timely setup of an optical light path to transport the soon-to-arrive payload. This is known as delayed reservation.
Purpose
The purpose of optical burst switching (OBS) is to dynamically provision sub-wavelength granularity by optimally combining electronics and optics. OBS considers sets of packets with similar properties called bursts. Therefore, OBS granularity is finer than optical circuit switching (OCS). OBS provides more bandwidth flexibility than wavelength routing but requires faster switching and control technology. OBS can be used for realizing dynamic end-to-end all optical communications.
Method
In OBS, packets are aggregated into data bursts at the edge of the network. Various assembling schemes based on time and/or size exist (see burst switching)Several edge router architectures have been proposed (see [1]). OBS features the separation between the control plane and the data plane. A control signal (also termed burst header or control packet) is associated to each data burst. The control signal is transmitted in optical form in a separated wavelength termed the control channel, but signaled out of band and processed electronically at each OBS router, whereas the data burst is transmitted in all optical form from one end to the other end of the network. The data burst can cut through intermediate nodes, and data buffers such as fiber delay lines may be used. In OBS data is transmitted with full transparency to the intermediate nodes in the network. After the burst has passed a router, the router can accept new reservation requests.
Advantages of OBS over OPS and OCS
In a OCS system, a lightpath must be set up from source to destination in the optical network. If the data transmission duration is short relative to the set up time, bandwidth may not be efficiently utilized in the OCS system. In comparison, OBS does not require end-to-end lightpath set up, and therefore may offer more efficient bandwidth utilization compared to an OCS system. This is similar to the advantage offered by packet switching over circuit switching.
OBS also offers advantages over OPS. Fully-fledged OPS requires optical buffer technology beyond what is currently available, as was previously explained. In order to overcome these shortcomings, delayed reservation schemes such as Just Enough Time are used. It has been shown that using the Just Enough Time delayed reservation scheme can create a throughput limitation in an electronic edge router in an OPS system [2]. This limitation can be overcome by using OBS [3]. OBS also reduces the processing requirements of the control plane in a router when compared to OPS. An router in an OPS network would have to perform processing operations for every arriving packet, wherelse in an OBS network the router performs processing operations for an arriving burst which contains several packets. Therefore, less processing operations per packet are required in an OPS network.
References
- ^ R. Rajaduray, "Unbuffered and Limited-Buffer All-Optical Networks", PhD dissertation, University of California, Santa Barbara, Dec. 2005, pp. 61 - 105
- ^ R. Rajaduray, "Unbuffered and Limited-Buffer All-Optical Networks", PhD dissertation, University of California Santa Barbara, December 2005, pp. 69 - 78, pp. 97 - 99
- ^ R. Rajaduray, "Unbuffered and Limited-Buffer All-Optical Networks", PhD dissertation, University of California Santa Barbara, December 2005, pp. 69 - 78, pp. 97 - 99
Additional reading
- Baldine I, et al., 2003, "Just-in-Time Optical Burst Switching Implementation in the ATDnet All-Optical Networking Testbed" Proceedings of the Global Telecommunications Conference (GLOBECOM 2003), San Francisco, USA.
- Chen, Yang; Qiao, Chunming and Yu, Xiang; "Optical Burst Switching (OBS): A New Area in Optical Networking Research", IEEE Network Magazine, Vol. 18 (3), pp. 16–23, May–June 2004.
- Gauger, C.; 2003, "Projects and Test Beds Related to OBS in Europe", Proceedings of the 2nd International Workshop on Optical Burst Switching, IEEE Globecom, San Francisco, USA.
- Jue, Jason P. and Vokkarane, Vinod M.; Optical Burst Switched Networks, Springer, Optical Networks Series, 2005 ISBN 0-387-23756-9.
- Garcia, Nuno; "Architectures and Algorithms for IPv4/IPv6-Compliant Optical Burst Swicthing Networks", PhD Thesis, University of Beira Interior, Covilhã, Portugal, 2008.
- R. Rajaduray, "Unbuffered and Limited-Buffer All-Optical Networks", PhD dissertation, University of California Santa Barbara, December 2005