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Routing and Wavelength Assignment in Wavelength Routing NetworksPowerPoint Presentation

Routing and Wavelength Assignment in Wavelength Routing Networks

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Routing and Wavelength Assignment (RWA) Problem Networks

- Given a set of connections, set up lightpaths by routing and assigning a wavelength to each connection
- Two constraints
- Wavelength continuity constraint: a lightpath must use the same wavelength on all the links along its path
- Distinct wavelength constraint: all lightpaths using the same link must be allocated distinct wavelengths

Two Versions of RWA Networks

- Static RWA
- Set of connections known in advance
- Goal is to minimize the number of wavelengths used

- Dynamic RWA
- Connection requests arrive sequentially.
- Setup a lightpath when a connection request arrives and teardown the lightpath after a finite amount of time
- Goal is to minimize connection blocking

Static RWA Networks

- An ILP (see handout)
- Solve routing and wavelength assignment jointly
- Objective: minimize the maximum flow (flow = # lightpaths passing through a link)

- Use the ILP to obtain the min number of wavelengths required:
- Pick a certain number of wavelengths, see if a solution can be found
- No - increase the number of wavelengths until a solution can be found.
- Yes - decrease the number of wavelengths until a solution can’t be found

Static RWA Networks

- Decompose into two sub-problems
- Routing
- Formulated as ILP
- Objective: minimize the maximum number of lightpaths on any link

- Wavelength assignment
- Reduce to graph coloring problem

- Routing

Static Wavelength Assignment Problem Networks

- Given a set of lightpaths and their routes, assign a wavelength to each lightpath
- Constraint: any two lightpaths sharing the same physical link are assigned different wavelengths
- Objective: minimize the number of wavelengths used

- Problem can be reduced to graph coloring
- Construct a graph G where nodes represents lightpaths, an edge exists between two nodes if the corresponding lightpaths pass through a common physical link
- Color the nodes in G such that no two adjacent nodes have the same color

Graph Coloring Networks

- NP-complete
- Sequential graph-coloring heuristic
- Vertices sequentially added to the portion of the graph already colored
- When add a vertex, assign it the smallest color not used by any of its neighbors

- Smallest-last ordering: assuming that the vertices vk+1, ..., vn have been selected, choose vk so that the degree of vk in the subgraph induced by V - {vk+1, ..., vn} is minimal.

Wavelength Converters Networks

- Wavelength converter: convert the wavelength of an input signal to a different wavelength
- Degree of Wavelength Conversion
- Full wavelength conversion: any input wavelength can be converted to any other wavelength
- Fixed wavelength conversion: an input wavelength can be converted to exactly one other wavelength
- Limited wavelength conversion: an input wavelength can be converted to a subset of the available wavelengths

Static RWA with Wavelength Conversion Networks

- If each node has full wavelength conversion capability
- Only need solve routing problem
- Minimizing the maximum flow will minimize the number of wavelengths used

Static RWA: a Layered Graph Approach Networks

- Route and assign wavelength to each connection one by one
- Use layered graph to deal with wavelength continuity constraint
- Create W copies of the network graph, W = number of wavelengths in a fiber
- RWA is solved by finding a path in one copy of the network graph

- Limited/fixed conversion: add links between layers

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