Chapter 10 RWA

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Chapter 10 RWA
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Routing and Wavelength Assignment for
Wavelength-Routed WDM Networks

• Combined routing and wavelength assignment
  problem
• Routing
• static ILP formulation
• Incremental
• connection requests arrive sequentially a
  lightpath is established for each connection and
  the lightpath remains in the network indenitely
• dynamic on-line algorithms
• a lightpath is set up for each connection request
  as it arrives and the lightpath is released after
  some finite amount of time
• Wavelength assignment
• static graph coloring approach
• dynamic heuristics
• A new wavelength assignment heuristic

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Static Lightpath Establishment (SLE) problem

• Static The set of connections is known in
  advanceDynamic Lightpath Establishment (DLE)
  problem
• Incremental Connection requests arrive
  sequentially, a lightpath is established for each
  connection, and a lightpath remains in the
  network indefinitely
• Dynamic A lightpath is set up for each
  connection request as it arrives, and the
  lightpath is released after some finite amount of
  time

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RWA

• Problem statement
• Wavelength-continuity constraint
• The SLE problem can be formulated as a mixed
  integer programming.
• The work in proposed practical approximation
  algorithms to solve the SLE problem for large
  networks and graph coloring problem.

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Combined Routing and Wavelength Assignment Problem
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Maximizing the number of established connection
(fixed W)
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Routing - ILP Formulation
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RWA with wavelength Conversion
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RWA with wavelength Conversion

• Sparse location of wavelength converters in the
  network
• Sharing of converters
• Limited-range wavelength conversion

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Routing - Algorithms For Dynamic Traffic

• Fixed routing (On/Off line)
• Fixed-alternate routing (On/Off line)
• Adaptive routing (On line)
• adaptive shortest path routing
• least congested path routing

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Fixed Routing

• Off-line calculation
• Shortest-path algorithm
• Dijkstras or
• Bellman-Ford algorithm
• Advantage
• simple
• Disadvantage
• high blocking probability and
• unable to handle fault situation

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Fixed-Alternate Routing

• Each node is required to maintain a routing table
  that contains an ordered list of a number of
  fixed routes to each destination node
• A primary route between s-d is defined as the
  first route
• An alternative route doesnt share any links with
  the first route (link disjoint)
• Advantage
• Provide some degree of fault tolerance
• Reduce the blocking probability compared to fixed
  routing

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Adaptive Routing

• The route from a source node to a destination
  node is chosen dynamically, depending on the
  network state
• Ex
• Shortest-cost-path routing
• Each unused link has the cost of 1 unit
• used link 8
• wavelength converter link c units.
• Disadvantage extensive updating routing tables
• Advantage lower blocking probability than fixed
  and fixed-alternate routing
• Least-congestion-path routing (LCP)
• Advantage
• Lower connection blocking than fixed and
  fixed-alternate routing

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Consider fault-tolerant

• Protection
• Set up two link-disjoint lightpaths
• Primary lightpath transmit data
• Backup lightpath must be reserved
• Fast but need reserve resource
• Restoration
• The backup path is determined dynamically after
  the failure has occurred
• Slow but doesn't need reserve resource

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Wavelength Assignment
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Wavelength Assignment Heuristics

• Random
• First-Fit
• Least-Used/SPREAD
• Most-Used/PACK
• Min-Product

• Least Loaded
• MAX-SUM
• Relative Capacity Loss
• Wavelength Reservation
• Protecting Threshold

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Static Wavelength Assignment

• Two lightpaths share the same physical link are
  assigned different wavelengths
• Reduced to graph-coloring problem
• 1.Construct a graph, such that each lightpath is
  represented by a node. There is one edge in
  between if two lightpaths share the same physical
  link.
• 2.Color the nodes such that no two adjacent nodes
  have the same colors.

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Static Wavelength-Assignment

• Minimizes the number of wavelengths used under
  the wavelength-continuity constraint reduced to
  the graph coloring problem
• Construct an auxiliary graph G(V,E)
• Color the nodes of the graph G
• Largest First
• Smallest Last

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Static Wavelength-Assignment (cont.)
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example
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Largest First
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Smallest Last
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First-Fit

• First available wavelength is chosen
• No global information needed
• Proffered in practice because of its small
  overhead and low complexity
• Perform well in terms of blocking probability and
  fairness
• The idea behind is to pack all of the in-use
  wavelengths towards lower end and continuous
  longer paths towards higher end

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FF example

• ?0 will be assigned
• ?0 will also be assigned MP and LL

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Least-Used (LU) Wavelength Assignment

• Least used in the network chosen first
• Balance load through all the wavelength
• Break the long wavelength path quickly
• Worse than Random
• global information needed
• additional storage and computation cost
• not preferred in practice
• Disadvantage
• This scheme ends up breaking the long wavelength
  paths quickly
• Additional communication overhead

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LU example

• ?0 ,?1 ,?3 are each used two links
• ?2 is used only one link
• So LU will choose ?2

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Most-Used (MU) Assignment

• Select the most-used wavelength in the network
• Advantages
• -outperforms FF, doing better job of packing
  connection into fewer wavelength
• -Conserving the spare capacity of less-used
  wavelength
• Disadvantages
• -overhead, storage, computation cost are similar
  to those in LU

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MU example

• ?0 ,?1 ,?3 are each used two links
• ?2 is used only one link
• So MU will choose one of ?0 ,?1 ,?3 with equal
  probability

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Notations
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Min-Product (MP)

• Used in multi-fiber network
• The idea is to pack wavelength into fibers,
  minimizing the number of fibers in the network
• ? D lj
• l ? p(p)
• for each wavelength j, 1?j ?W.
• Chose a set of wavelength j minimizing the above
  value
• Disadvantage not better that multi-fiber version
  of FF
• -introduce additional computation costs
• -

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MP example
0
1
2
3
4
5
?12 ?23 ?31
?13 ?22 ?32
?11 ?24 ?31
?13 ?21 ?32
?15 ?22 ?31
?1 2313590 ?2 3241248 ?3
121214 So choose ?3
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Least-Loaded (LL) Assignment

• Multi-fiber network
• Select the wavelength that the largest residual
  capacity in the most-loaded link along route p.
• Advantage outperforms MU and FF in terms of
  blocking probability
• LL selects the minimum indexed wavelength j in Sp
  that achieves

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LL example
0
1
2
3
4
5
Assume 7 fibers per link
?12(5) ?23(4) ?31(6)
?13(4) ?22(5) ?32(5)
?11(6) ?24(3) ?31(6)
?13(4) ?21(6) ?32(5)
?15(2) ?22(5) ?31(6)
Set up lightpath from 0 to 2 Choose ?3
Max(min(residual capacity))5
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MAX-SUM Assignment

• Applied to multi-fiber and single-fiber also
• Before lightpath establishment, the route is
  pre-selected
• After lightpath establishment, it attempts to
  maximize the remaining path capacity

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MAX-SUM Assignment (continued)
r(?, l, j) Mj - D(?) lj r(?, l, j)link
capacity, the number of fibers on which
wavelength j is unused on link l r(?, p, j) min
r(?, l, j) l ? p(p) r(?, p, j)the
number of fibers on which wavelength j is
available on the most-congested like along the
path p
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MAX-SUM (MS)

• MSconsiders all possible paths in the network and
  attempts to maximize the remaining path
  capacities after lightpath establishment

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MAX-SUM Assignment (continued)
w R(?,p) S min
r(?, l, j) j1 l ? p(p) At last,
chose the wavelength j that maximizes the
quantity S R(?(j) ,p) p?P ?(j) be the next
state of the network if j is assigned P is all
the potential paths for the connection
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MSexample
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Calculation of Max-Sum
wavelengths
P1(2,4)
?3
?2
?1
WPC Wavelength-path Capacity
?0
0
1
2
3
4
5
6
Wavelength selected ?0, ?1, or ?3
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Relative Capacity Loss (RCL) Assignment

• Chose wavelength j to minimize the relative
  capacity loss
• S (r(?, p, j) - r(?(j), p, j))/ r(?, p, j)
• p?P
• Sometimes better than MAX-SUM
• -MAX-SUM could cause blocking
• Longer lightpaths have a higher block probability
  than shorter ones
• Some schemes to protect longer paths
• Wavelength reservation (Rsv) and protesting
  threshold (Thr)

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Relative Capacity Loss (RCL)

• MS
• RCL

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RCL example
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Illustrative Example
Note control network not shown. All wavelengths
shown are for data traffic
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Calculation of Relative Capacity Loss
wavelengths
P1(2,4)
?3
?2
Wavelength selected ?1 or ?3
?1
?0
0
1
2
3
4
5
6
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Random Wavelength Assignment

• Randomly chosen available wavelength
• Uniform probability
• No global information needed

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Simulation Network
2
1
2
1
1
0
3
1
1
1
1
5
4
2
Connection management protocol link-state
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Computational Complexity

• Wavelength reservation Protecting threshold -
  constant
• Random First-Fit - O(W)
• Min-Product Least-Loaded - O(NW)
• Least-Used Most-Used - O(LW)
• Max-Sum Relative Capacity Loss - O(WN3)
• where W - of wavelengths, N - of nodes, L -
  of links

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Distributed Relative Capacity Loss (DRCL)

• Speed up the wavelength-assignment procedure
• each node stores information on the capacity loss
  on each wavelength
• only table lookup
• small amount of calculation are required upon the
  arrival of a connection request
• Routing is implemented using the Bellman-Ford
  (each node exchange table with its neighboring
  nodes and updates its table)

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Distributed Relative Capacity Loss (DRCL) (cont.)

• DRCL considers all of the paths from the source
  node of the arriving connection request to every
  other node ,excluding the destination node of the
  arriving connection request
• DRCL choose the wavelength that minimize the sum
  of rcl(w,d) over all possible destination d

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DRCL example
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Distributed RCL Algorithm
P1(2,4)
?3
?2
?1
?0
0
1
2
3
4
5
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RCL table at Node 2
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Characteristics of Distributed RCL

• Less state information is exchanged
• Faster computation of wavelength assignment upon
  a connection request
• Can be combined with adaptive routing

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Simulation Network
2
1
2
1
1
0
3
1
1
1
1
5
4
2

• Average propagation delay between two nodes
  0.107 ms
• Average hop distance 1.53

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Simulation Results of Distributed RCL
Comparison of DRCL with adaptive routing and
RCL with fixed routing
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Conclusion for RWA
L of links, N of nodes, W of wavelengths
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Future Research

• Survivable wavelength-routed WDM networks
• previous work static traffic single link
  failure S. Ramamurthy 1998
• higher layer protection -logical topology design
  with bundle cut in mind
• WDM layer protection - dynamic traffic

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Future Research (Contd)

• Managing multicast connections in
  wavelength-routed WDM networks
• KMB
• Bellman-Ford
• Chain

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Simulation Results
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Simulation Results (cont.)
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Simulation Results (cont.)
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Simulation Results (cont.)