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Service Differentiation in Optical Burst Switched Networks

This paper discusses a novel approach to service differentiation in Optical Burst Switched Networks (OBS) through proportional Quality of Service (QoS). It addresses the challenges of maintaining predetermined loss rates for various classes of packets, which are prioritized by their importance. The method utilizes a preemptive wavelength reservation system to ensure that in-profile requests are serviced while controlling excess dropping of packets. Analytical and simulation results demonstrate the effectiveness of this mechanism, showcasing lower blocking probabilities and improved resource utilization.

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Service Differentiation in Optical Burst Switched Networks

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  1. Service Differentiation in Optical Burst Switched Networks Chi-Hong Loi, Wanjiun Liao, and De-Nian Yang GLOBECOM’02

  2. Proportional QoS • The loss rate of each class is maintained in a predefined proportion according to the priority. • An arrival packet will be dropped if its predefined loss rate is violated regardless of whether there is an idle channel. • This approach always causes excessive dropping.

  3. Protocol Fundamentals • There are k different classes c1, c2, …,ck with ascending priority order. • Let pi be the usage limit assigned to class ci. 0 ≤ p1 < p2 < … < pk ≤ 1, and . • Usage profile: • Usage limit. • Current usage. • List of scheduled requests in the same class (burst duration outgoing wavelength and a predefined timer).

  4. In-Profile Verification • A class is said to be in profile if its current usage does not exceed a predefined usage limit. • The current usage of class ci is defined as where nj is the number of scheduled requests of class cj in (t, t+τ), and lj is the burst length of request Rj. • Class ci is in profile if ρi ≤ pi; otherwise, the class is out of profile.

  5. Burst Preemption • Suppose that a switch has newly received a in-profile class request Rx, with start time sx and end time ex. • Let Co be a set of candidate classes to be preempted, defined as • Co = {ci | ρi > pi, i = 1, 2, …k}

  6. New Burst No No Eligible? Dropped In-profile? Yes Yes Find a previous request from out-of-profile class and make a preemption. Scheduled Update profile Operation Overview

  7. Analytical Results Let denotes the state of the Markov chain, where ni is the number of wavelengths used by class ci.

  8. Analytical Results (continued)

  9. Simulation Results • Blocking probabilities of the three mechanisms.

  10. Simulation Results (continued) • Blocking probabilities of the three mechanisms with network congestion.

  11. Simulation Results (continued) • System utilization.

  12. Conclusion • A new bufferless mechanism was described using a preemptive wavelength reservation mechanism to differentiate services in OBS networks. • The approach performs best in terms of lower blocking probability and higher resource utilization.

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