Adaptive Wavelength Routing in All-Optical Networks

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Adaptive Wavelength Routing in All-Optical
Networks

• A. Mokhtar and H.S. Azizglu,IEEE/ACM
  Transactions on Networking,April, 1998.

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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, wwo wavelength
  conversion, wavelength reuse.

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• 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

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• 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/Adaptive Unconstrained Routing (AUR)

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• 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

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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))

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• 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 k1,2,,l and some j.
• The optimal RWA minimizes the call-blocking
  probability among all assignments.
• Fixed routingAdaptive routing with different
  sorting mechanisms
• PACK most utilized wavelength first
• SPREAD least utilized wavelength first
• RANDOM in random order
• EXHAUSTIVEall paths
• FIXED in fixed order

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III. Analysis of Fixed and Alternate Routing

• Fixed and Alternate routing Fixed-Order Search
  of wavelength set
• A. Single-Fiber Networks nodes are
  interconnected by single-fiber linksB.
  Multiple-Fiber Networks nodes are interconnected
  by multiple-fiber links

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A. Single-Fiber Networks

• (Fig. 2)

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B. Multiple-Fiber Networks

• (Fig. 3)
• An attractive alternative to a networkwith
  wavelength conversion (Fig. 4)

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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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• (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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• (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
• W4 is more accurate than that W8Random Network
  is more accurate than ARPA-2 (Note accurate
  means analysis is closer to simulation)

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• (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
  W8 and Pb10-3, 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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• (Fig. 17) Blocking Prob. For Random with Multiple
  Fibers
• 1. Alternate Routing with M22. Fixed Routing
  with M2 3. Alternate Routing with M14. Fixed
  Routing with M1
• 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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• (Fig. 18) Blocking Prob. Vs Load per Fiber For
  Random with Fixed Routing
• 1. M22. M1
• M2 can handle double the load of M1
• Similar for Alternate Routing
• (Fig. 19) Blocking Prob. For Random with Partial
  Wavelength Conversion
• 1. M1, W8 (slightly better)2. M2, W4
• Partial Wavelength Conversiondoubling the
  number of fibers per link doubling the number
  of wavelengths per links

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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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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 routinghowever,
  as the number of alternate routes increases, the
  performance approaches that of AUR.

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• 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.