Deflection Routing Strategies in Optical Burst-Switched Networks Halima Elbiaze Department of Computer Science UQAM Case postale 8888, Succursale Centre-ville Montral (Qc) H3C 3P8 Canada Telephone: (514) 987–3000 (8485) Email: halima.elbiaze@uqam.ca Brigitte Jaumard Department of Computer Science and Operations Research Universit´ e de Montr´ eal C.P. 6128, succursale Centre-ville Montr´ eal (Qc) H3C 3J7 Canada Telephone: (514) 343–7478 Email: jaumard@iro.umontreal.ca Ammar Metnani Department of Computer Science and Operations Research Universit´ e de Montr´ eal C.P. 6128, succursale Centre-ville Montr´ eal (Qc) H3C 3J7 Canada Email: metnania@iro.umontreal.ca Abstract— Optical Burst Switching (OBS) is a very promising technology for the next generation optical Internet as it offers a more efficient bandwidth utilization and a great potential for an efficient integration of IP and WDM technologies. However, several critical issues still need to be solved such as contention resolution without optical buffering. Contention arises when two or more bursts compete for the same output fiber on the same wavelength at the same time. It is a key determinant of packet-loss performance with a significant impact on network performance. In this paper, we propose and evaluate three new deflection routing strategies which aim at resolving contention. They lead to significant better network performance when compared with the most recent contention resolution schemes proposed in the literature. One of the drawbacks of the deflection routing mechanisms discussed in the literature is their lack of ability for computing alternative paths based on clear design constraint. The proposed deflection strategies are based on different alter- native path computing methods: i) Shortest Path(SP), ii) Latest Available Unused Channel with Void Filling (LAUC-VF) and iii) Least Used Wavelength (LUW). Simulation under different traffic assumptions have been conducted on the EONET network to analyze and compare the three new deflection routing strategies. keywords : Optical Burst Switching (OBS), deflection routing, WDM (Wavelength Division Multiplexing). I. I NTRODUCTION Optical Burst Switching (OBS) [1] [2] together with Optical Packet Switching (OPS) have been proposed as switching paradigms with a number of attractive advantages, such as faster speed, finer granularity, and more efficient bandwidth utilization than optical circuit switching (Xu, Perros and Rouskas [3]). OBS and OPS are therefore promising technolo- gies for the next generation optical Internet. While OPS pro- totypes are still in the laboratories and are not necessarily well tailored to variable-length IP traffic, OBS offer an alternative that somehow combines the advantages of wavelength routing and OPS as it provides a trade-off between coarse-granularity wavelength routing and fine-granularity optical OPS. For instance, in optical burst switching, the transmission link carry multiple WDM channels, which can be dynamically assigned to user data bursts. Moreover, OBS uses out-of-band signaling, i.e., one channel on each link is reserved for control information. This control and data separation both simplifies the data path implementation and makes the use of optical switching technologies more efficient. At the network edge, a control packet is sent on the control channel ahead of the variable-length data burst. Its role is to reserve bandwidth resources for each corresponding data burst. At the intermediate nodes, the control packet is electronically processed, while the data channels are switched through transparently. Due to the OBS one-way reservation paradigm, bursts can be blocked in intermediate nodes due to resource contention, i.e., more than one burst going out want to use the same output port at the same time. In order to reduce dropping probability (DP), a contention resolution mechanism is required. Optical buffering, wavelength conversion and deflection routing are all technologies that can be used to resolve the contention in OBS networks. For the buffering-based solution, fiber delay lines (FDLs) and/or circulating loops can be used to temporarily store the bursts until the resources become available. However, since today optical buffers are typically limited to providing a few tens of μs delay, it is difficult to store longer optical bursts. In addition, the optical buffer implementation requires a significant amount of hardware as well as complex electronic controls. On the other hand, contention can be resolved in spectral dimension using wavelength conversion. Several studies have shown the performance improvement that this technology can provide. However, optical converters are still immature tech- nology due to their complex and expensive implementation in switch fabrics. Therefore, they are kept far from practical use and that is why we did not consider this contention resolution scheme in the current study. The paper is organized as follows. First, we review briefly the current works on deflection routing as a potential scheme for contention resolution. Next, in Section III, we propose and describe three new strategies for deflection routing. Simula- tions and a comparative study are discussed in Section IV on the EONET network, a much larger network and traffic instance