Optical WDMA network design and function placement

The parallel use of multiple channels in a WDM star network means that too many packets may simultaneously arrive for the same destination station, ne cessitating the implementation of a destination-conflict-resolution functio n somewhere within the network. This paper considers explicitly, the placem ent of the destination-conflict-resolution function which specifies the loc ation(s) where it should be performed, and when it should be performed. Tra ditional placements in which the function is located at all user stations a nd performed either before packet transmission (using the request-schedule- then-transmit principle) or after a destination conflict has been detected (using the detect-and-retransmit-if-lost principle), is compared with a cen tral placement in which only one central station located at the entrance to the star coupler is responsible for detecting conflicts and optically buff ering 'otherwise lost' packets whilst they are en route to their destinatio ns, until their destinations are free to receive them. The networks are eva luated considering their delay and throughout characteristics, the computat ional complexity of their protocols, their fault tolerance, and their hardw are demands. The results presented suggest that significant performance imp rovements are achievable with the central placement since destination confl icts are resolved without having to retransmit packets nor waiting until th e end of a request-broadcast-and-schedule phase before a given packet can b e transmitted. The central station works with Space Division Multiplexed si gnals, just before they enter the star coupler. Its implementation is there fore simpler than when all stations are charged with this task, each of whi ch has to attend to multiple WDM channels. Only 'otherwise lost' packets ar e buffered so the network has low buffer memory requirements. (C) 1999 Else vier Science B.V. All rights reserved.