DQOBSR Protocol with QoS Provisioning for OBS Metro Rings

Optical burst switching (OBS) is the switching technology that enables optical internet with current technology. OBS networks are capable of operating with or without optical buffers and wavelength converters. Hence, medium access control (MAC) protocol plays an important role in resolving contention in such networks. Distributed Queue OBS Ring (DQOBSR) is one MAC protocol proposed for OBS ring networks. In this paper, the quality of service (QoS) provisioning scheme for DQOBSR protocol is presented. For the proposed protocol, service differentiation for different classes of traffic in terms of throughput and access delay is verified through simulation. A mathematical model is also presented for the computation of classwise mean access delay. The results obtained using the model are found to be in good agreement with the simulation results. 1. Introduction OBS is seen as the prospective solution for optical internet that enables efficient utilization of the fiber, withstanding the current technological limitations [1]. In OBS, contention resolution is one of the most important issues, since the network is provided with limited or no optical buffers. An effective method of addressing the contention is selecting an appropriate MAC protocol. A new MAC protocol, namely, distributed access OBS (DAOBS) is proposed for OBS rings in [2], and later it had been extended for mesh topologies [3]. This protocol is an adaptation of distributed queue dual bus (DQDB) to OBS ring networks. For the case of ring topology, DQOBSR protocol [4] is proposed with simpler bus assignment without compromising the performance. In this paper, the QoS provisioning for DQOBSR-based networks is presented, and the performance is analyzed through simulation and mathematical modeling. 2. Overview of DQOBSR Protocol The topology for the DQOBSR protocol consists of two unidirectional counter rotating rings similar to fiber distributed data interface (FDDI). The capacity of each ring is split into data channels and two control channels. The schematic diagram of the network implementing the DQOBSR MAC protocol is shown in Figure 1. Each wavelength channel is divided into equal length slots. The control slots are further split into number of minislots, and there is a one-to-one correspondence between the minislots and the number of data channels. The control slot format is shown in Table 1. Table 1: Control slot format. Figure 1: Schematic diagram of the network implementing DQOBSR protocol. The nodes implement a firsti-first-out (FIFO) distributed queue similar to the one used with DQDB