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Routing and Wavelength Assignment in Wavelength Routing Networks - PowerPoint PPT Presentation

Routing and Wavelength Assignment in Wavelength Routing Networks. Routing and Wavelength Assignment (RWA) Problem. Given a set of connections, set up lightpaths by routing and assigning a wavelength to each connection Two constraints

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Routing and Wavelength Assignment in Wavelength Routing 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

• 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

• If each node has full wavelength conversion capability

• Only need solve routing problem

• Minimizing the maximum flow will minimize the number of wavelengths used

• 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