How the data requests will be served in Optical - WDM Networks ?
In Optical WDM Networks, when ever a data request arrives at a Node, first it validates the request, during this process all the headers in the request will be validated, after validating request it identifies the source node and destination node addresses. Once it get the Source-Destination pair it will assign a route and wavelength to transmit. This assignment is valid till all the data is transmitted.
What is RWA?
RWA -- "Routing and Wavelength Assignment", As described above once a node identifies source and destination pair the process of assigning a route and wavelength is called as RWA Protocol. There are many RWA protocols exists and depends on the requirement and network type the protocol will be choose or implemented.
What are the main network types in WDM Networks?
Mainly there two types of Network architecture but these days hybrid implementation also being used so we can say three types. They are Distributed Networks, Centralized Networks and Hybrid or Global Networks.
In Distributed Networks each and every node in network will have the information of entire network structure, in future if there is any new node added or removed that information need to be updated at all the nodes in network. Along with this each node maintain a minimum information of paths between source and destination pair. It also keep track of wavelengths assigned.
In Centralized Networks all the network information will be stored at Central Management System and every request will be processed or served by CMS. In this case if there is any modification in network then it is enough if we update only at CMS. But major dis advantage is when there is failure in CMS the entire network will be down. In order to avoid this in the design people will maintain the backup CMS also.
In hybrid or Global Networks, they will use the combination of both Distributed and Centralized Network types, means small small groups will in Centralized manner and all these CMS will be a part or act as nodes of a Distribute Network. The major advantage of this is if there is any failure in network a particular group or very few number of devices will be affected.
Why RWA is challenge?
There are many routing and wavelength assignment techniques are available and depends on the technique the cost, delay, resource utilization and QoS are effected. If we use standard technique like shortest path algorithm then there is more chance of congestion in the network, If use the Wavelength Continuity Constraint WCC algorithm then cost of request can be reduced but the number of calls or requests served will be limited. If we choose a path based on blocking of calls then there is a chance of choosing a long path though which latency increases. Like this many other techniques are available for RWA so based on our requirement we need to select which algorithm is suitable like shortest path, Less blocking path. Wavelength also need to be choosed based on requirement like least used, most used, WCC or some other. So ultimately RWA plays an important role in network Quality of Service. The major contributors are the number of nodes on path, number of wavelength conversions required and number of wavelengths are utilized on links.
