Channel Access Protocols for High-Speed LANs Using WDM: A Comparative Study

Extensive research and considerable progress in the dense optical wavelength division multiplexing (WDM) technology has made it the most likely candidate for implementation in next-generation high performance switches, LANs and MANs. The first key challenge is the continuous development of cost-effective optical components in order to realize practical networks. The next main challenge is to design an effective channel access protocol that will: (a) take full advantage of the existing and emerging optical technologies, (b) fairly and successfully coordinate transmissions between the networks nodes, and (c) efficiently manage the enormous fiber bandwidth. There have been many access protocols proposed for WDM networks including quite a few proposals that require many more channels than the number of nodes. The practical device characteristics impose an upper limit on the number of available WDM channels. Our focus in this paper is on systems with many nodes and small number of channels. We study the use of in-band signaling mechanism compared to the separate control channel (out-band signaling) approach. Signaling is used to achieve coordination between source and destination with respect the communication channel. The objective of this paper is to understand the key trade-offs in the protocol design for such networks through close examinations of the two approaches. Our intent is not to claim the superiority of either approach, rather to stimulate further studies on such systems.