Stabilizing deflection routing in optical burst switched networks

Abstract

Abstract-This paper studies the blocking performance of optical burst switching (OBS) networks using a sequential office control (SOC) state-independent deflection routing policy. We show that unprotected deflection routing may destabilize OBS resulting in higher blocking probabilities than if bursts were not deflected but simply blocked. This study was motivated by the well-known destabilizing effect that alternative routing has on circuit switching in classical telephony networks. We propose two forms of protection to guard against destabilization: 1) wavelength reservation, which is analogous to trunk reservation in circuit switching; and, 2) preemptive priority, which is a new form of protection where bursts that have not been deflected are given preemptive priority over bursts that have been deflected. Our main contribution is a one-moment reduced-load approximation to evaluate the blocking performance of OBS networks using deflection routing protected by either wavelength reservation or preemptive priority. Our reduced-load approximation relies on the usual assumptions of link independence and Poisson distributed link arrivals. We quantify the error admitted in making these two assumptions via simulation. Using our reducedload approximation, we evaluate the blocking performance of protected and unprotected deflection routing in several randomly generated networks. The chief conclusion of our study is that deflection routing in OBS should be given some form of protection to avoid destabilization resulting from upward load variations, and in terms of blocking performance, preemptive priority is the best form of protection for OBS. We use simulation to verify that our conclusions remain valid for a realistic traffic scenario.

Deflection Routing in OBS Networks

“…This wavelength reservation scheme alleviates the destabilizing effect and increases the throughput at high loads. Preemptive priority is a similar method in which a first-choice burst is given the right to preempt a reservation that has been scheduled for a deflected burst [19]. Preemptive priority has a negligible effect on blocking during stable periods and guarantees protection against destabilization during overloads.…”

Buffering-deflection tradeoffs in optical burst switching

“…This assumption has been used extensively in the technical literature dealing with performance evaluation of OBS networks, e.g. [9,10,[12][13][14]20]. The inherent simplicity given by this assumption makes us focus on evaluating how the different network and node parameters affect the network performance.…”

“…As a matter of fact, the technical literature does not provide yet an analogous understanding of the effect of optical buffering in OBS networks. On the routing issue, deflection routing applied to OBS has been already reported in [8][9][10][11][12][13][14], albeit without, or just partially, outlining the combined effect with node buffering. Several contention resolution schemes, including buffering and deflection, have been compared for traffic performance [15]; however, they refer to an OPS scenario quite different from an OBS one.…”

Performance Evaluation of Slotted Optical Burst Switching Systems With Quality of Service Differentiation

“…Eq. (8) can be solved for after replacing by as follows: (10) Similarly (9) can be simplified after replacing : (11) Substituting found in (10) into (11), we end up with the following equality: (12) Eq. (12) should be solved for maximum for which the following inequality inherited from (10) is satisfied: (13) The computations of the maximum value of for which (12) can be solved such that (13) is satisfied do not have a simple closed form solution.…”

“…The most common technique for contention resolution in OBS networks is wavelength conversion [9], [10] although other contention resolution techniques such as fiber delay lines (FDL) [11] or deflection routing can also be used [12]. We assume in the current paper that the OBS system employs only full wavelength conversion for contention resolution where a burst arriving on a certain wavelength can be switched onto any other idle wavelength towards its destination.…”