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Adaptive Wavelength Routing in All-Optical Networks

Adaptive Wavelength Routing in All-Optical Networks. A. Mokhtar and H.S. Azizglu, IEEE/ACM Transactions on Networking, April, 1998. I. Introduction. All-Optical Network signals remain in the optical domain from the source to the destination, thereby, eliminating the electrooptic bottleneck.

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Adaptive Wavelength Routing in All-Optical Networks

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  1. Adaptive Wavelength Routing in All-Optical Networks A. Mokhtar and H.S. Azizglu,IEEE/ACM Transactions on Networking,April, 1998.

  2. 2 I. Introduction • All-Optical Network • signals remain in the optical domain from the source to the destination, thereby, eliminating the electrooptic bottleneck. • Two architectures: • Broadcast-and-Select • for LAN: N x N passive broadcast star, simple. • Wavelength Routing (Fig. 1) • for WAN: optical switch, w|wo wavelength conversion, wavelength reuse.

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  4. 4 • Routing Classification - when: • Static: does not vary with time • Adaptive: vary with time, use of network state information • Routing Classification - path assignment: • Fixed: a single path / s-d pair • Alternative: a set of paths / s-d pair • Routing Classification - path selection from: • Constrained: a subset of all possible paths • Unconstrained: all possible paths

  5. 5 • Wavelength-Routing Components (Phases): • Path Selection: to determine a path; • Wavelength Assignment: to assign a wavelength to the selected path. • without wavelength conversion • with wavelength conversion • Wavelength Assignment: • Fixed-order search • Adaptive-order search • In this paper: • Fixed/AdaptiveUnconstrained Routing (AUR)

  6. 6 • Previous works: • Chlamtac et al: • fixed routing + fixed-order wavelength search • Birman and Kershenbaum: • fixed and alternate routing + wavelength reservation with threshold protection • Birman: • Calculates approximate blocking probabilities for fixed routing with random wavelength allocation • Harai et al: • alternate routing with random wavelength allocation • Bala et al: • adaptive ordering according to the utilization • Lee and Li: • unconstrained routing with an exhaustive search

  7. 7 II. Routing and Wavelength Assignment Algorithms • For K links and W wavelengths, the state of link i, 0  i  K-1 at time t: • a column vectort(i) = (t(i)(0), t(i)(1),…, t(i)(W-1))T,wheret(i)(j)= 1 if wavelength is utilized by some connection at time t, 0 otherwise. • The state of the network at time t: • a matrixt = (t(0), t(1),…, t(k-1))

  8. 8 • The Routing and Wavelength Algorithm (RWA) searches for a path P=(i1,i2,…,il)from the source to the destination such thatt(ik)(j)=0 for all k=1,2,…,l and some j. • The optimal RWAminimizes thecall-blocking probability among all assignments. • Fixed routing:Adaptive routing: with different sorting mechanisms • PACK: most utilized wavelength first • SPREAD: least utilized wavelength first • RANDOM: in random order • EXHAUSTIVE:all paths • FIXED: in fixed order

  9. 9 III. Analysis of Fixed and Alternate Routing • Fixed and Alternate routing + Fixed-Order Search of wavelength set • A. Single-Fiber Networksnodes are interconnected by single-fiber linksB. Multiple-Fiber Networksnodes are interconnected by multiple-fiber links

  10. 10 A. Single-Fiber Networks • (Fig. 2)

  11. 11 B. Multiple-Fiber Networks • (Fig. 3) • An attractive alternative to a networkwith wavelength conversion (Fig. 4)

  12. 12 IV. Numerical Results • ARPA-2 Network (Fig. 5)Randomly Generated Topology (Fig. 6) • (Fig. 7) Blocking Prob. For ARPA-2 with 4 Wavelengths(Fig. 8) Blocking Prob. For ARPA-2 with 8 Wavelengths(Fig. 9) Blocking Prob. For Random with 4 Wavelengths(Fig. 10)Blocking Prob. For Random with 8 Wavelengths • 1. AUR/Exhaustive (higher complexity)2. AUR/Pack3. AUR/Random4. AUR/Spread5. Fixed Routing

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  15. 15 • (Fig. 11)Blocking Prob. For ARPA-2 with 4/8 Wavelengths(Fig. 12)Blocking Prob. For Random with 4/8 Wavelengths • 1. AUR/Pack2. AUR/FixedBut, AUR/Fixed is closed to AUR/Pack and has lower complexity than AUR/Pack.Hence, AUR/Fixed is a good compromise between good blocking performance and moderate complexity

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  17. 17 • (Fig. 13)Analysis vs Simulation for ARPA-2 with 4/8 W.L. (Fig. 14)Analysis vs Simulation for Random with 4/8 W.L • W=4 is more accurate than that W=8Random Network is more accurate than ARPA-2 (Note: accurate means analysis is closer to simulation)

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  19. 19 • (Fig. 15)Blocking Prob. For Random with 4 Wavelengths(Fig. 16)Blocking Prob. For Random with 8 Wavelengths • 1. AUR/Exhaustive2. AUR/Pack3. Alternate Routing (AR)4. Fixed Routing (FR)But, When W=8 and Pb=10-3, throughput gap between FR and AR is 70% and throughput gap between AR and AUR/Pack is 50%.Hence, Alternate Routing is a practical tradeoff between Fixed Routing and AUR

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  21. 21 • (Fig. 17)Blocking Prob. For Random with Multiple Fibers • 1. Alternate Routing with M=22. Fixed Routing with M=23. Alternate Routing with M=14. Fixed Routing with M=1 • Blocking performance improves with two fiberswith throughput increased by an factor of 4 • Throughput gain of Alternate Routing becomes more significant with two fibers.

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  23. 23 • (Fig. 18)Blocking Prob. Vs Load per Fiber For Random with Fixed Routing • 1. M=22. M=1 • M=2 can handle double the load of M=1 • Similar for Alternate Routing • (Fig. 19)Blocking Prob. For Random with Partial Wavelength Conversion • 1. M=1, W=8 (slightly better)2. M=2, W=4 • Partial Wavelength Conversion:doubling the number of fibers per link = doubling the number of wavelengths per links

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  25. 25 V. Complexity Analysis • (Table I and II)Average number of wavelength searchesnormalized by the number of wavelengths • 1. Spread2. Random3. Fixed (closed to Pack)4. Pack5. Exhaustive (=1)

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  27. 27 VI. Conclusions • All-paths selection affects the blocking performance considerably, especially with light load and relatively large number of wavelengths. • Unconstrained routing improves in the call-blocking performance over constrained routing. • AUR outperforms fixed routing. • AUR also outperforms alternate routing;however, as the number of alternate routes increases, the performance approaches that of AUR.

  28. 28 • The performance gains with Adaptive Routing are more pronounced in denser network topologies as AUR takes advantage of higher network connectivity. • Incorporating network state information about wavelength utilization into the wavelength selection process is of second importance as it results in marginal improvement in the call-blocking probability. • Alternate routing is a good tradeoff between fixed routing and AUR. • Multiple-fibers networks are an attractive alternative for networks with wavelength conversion.

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