Adaptive Hybrid Deflection and Retransmission Routing for Optical Burst-Switched Networks

Adaptive Hybrid Deflection and Retransmission Routing for Optical Burst-Switched Networks Martin L´evesque, Halima Elbiaze Department of Computer Science Universit´e du Qu´ebec `a Montr´eal Montr´eal (QC), Canada Email: elbiaze.halima@uqam.ca Wael Hosny Fouad Aly Department of Computer Engineering Arab Academy for Science & Technology Alexandria, Egypt Email: drwaelhosny@aast.edu Abstract—Burst contention is a well known challenging problem in Optical Burst Switching (OBS) networks. Deflection routing is used to resolve contention. Burst retransmission is used to reduce the Burst Loss Ratio (BLR) by retransmitting dropped bursts. Previous works show that combining deflection and retransmission outperforms both pure deflection and pure retransmission approaches. This paper proposes a new Adaptive Hybrid Deflection and Retransmission (AHDR) approach that dynamically combines deflection and retransmission approaches based on network conditions such as BLR and link utilization. Network Simulator 2 (ns-2) is used to simulate the proposed approach on different network topologies. Simulation results show that the proposed approach outperforms static approaches in terms of BLR and goodput. I. INTRODUCTION Optical Burst Switching (OBS) [1] is a promising technology to handling bursty and dynamic Internet Protocol traffic in optical networks effectively. In OBS networks, user data (IP for example) is assembled as a huge segment called a data burst which is sent using one-way resource reservation. The burst is preceded in time by a control packet, called Burst Header Packet (BHP), which is sent on a separate control wavelength and requests resource allocation at each switch. When the control packet arrives at a switch, the capacity is reserved in the cross-connect for the burst. If the needed capacity can be reserved at a given time, the burst can then pass through the cross-connect without the need of buffering or processing. Since data bursts and control packets are sent out without waiting for an acknowledgment, the burst could be dropped due to resource contention or to insufficient offset time if the burst catches up the control packet. Thus, it is clear that burst contention resolution approaches play an essential role to reduce the Burst Loss Ratio (BLR) in OBS networks [2]. Burst contention can be resolved using several approaches, such as wavelength conversion, buffering based on fiber delay line (FDL) or deflection routing. Another approach, called burst segmentation, resolves contention by dividing the contended burst into smaller parts called segments, so that a segment is dropped rather than the entire burst. Deflection routing is the most attractive solution to resolve the contention in OBS networks, because it does not need added cost in terms of physical components and uses the available spectral domain. However, as the load increases, deflection routing could lead to performance degradation and network instability. Since deflection can not eradicate the burst loss, retransmission at the OBS layer has been suggested by Torra et al. [3]. A static combination of deflection and retransmission has been proposed by Son-Hong Ngo et. al. [4]. They have proposed a Hybrid Deflection and Retransmission (HDR) algorithm [4] which combines deflection routing and retransmission. Simulation results have shown that HDR gives bad overall performance because it systematically try deflection first. To overcome this shortcoming, the authors have developed another mechanism called Limited Hybrid Deflection and Retransmission (LHDR) that limits the deflection. This paper introduces a novel algorithm to combine deflection routing and retransmission called Adaptive Hybrid Deflection and Retransmission (AHDR). A success probability threshold function is used to dynamically make the decision of using either the deflection or the retransmission based on local knowledge about network conditions. In order to make this local knowledge feasible, AHDR algorithm exploits sending and receiving of Positive Acknowledge- ment (ACK) and Negative Acknowledgement (NACK) messages to advertize useful statistics about the network conditions stored by all nodes. This paper is organized as follows. Section II describes the proposed Adaptive Hybrid Deflection and Retransmission (AHDR) algorithm. Section III presents simulation results. Finally, Section IV contains the conclusion and future possible works. II. ADAPTIVE HYBRID DEFLECTION AND RETRANSMISSION In this section, we describe the proposed algorithm (AHDR). AHDR optimizes the decision of doing either a deflection or a retransmission. It also enhances the selection of an alternate route. A. Transferring statistics between nodes Once the control packet reaches the destination, an ACK is sent to the source. If the control packet is dropped, then the proposed algorithm uses a NACK to notify the source for burst retransmission. AHDR does not only use the ACK and the NACK for notification but it uses them also to transmit

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