Microsoft Word - 444-383.rtf

-In this paper we study the effect of round trip propagation delay in performance measures of Wavelength Division Multiplexing (WDM) networks. Even though the impact of propagation delay is substantial in optical networks behavior, most of the studies ignore the effect of this object in throughput and delay evaluation. We assume a WDM Local Area Network (LAN) where the round trip propagation delay is less or equal to a data packet transmission time. The proposed asynchronous transmission policy avoid data channel collision. In the analysis we take into account the propagation delays and the effect of receiver collision for a system with finite number of stations. Key-Words: Wavelength Division Multiplexing, round trip propagation delay, receiver collision, ErlangB formula, average rejection probability. 1. Network Architecture Model The system under consideration as Figure 1 shows is a passive star network. The system uses 1 + N wavelengths, N λ λ λ ,..., , 1 0 , to serve a finite number ) ( N M M > of stations. The system at wavelength 0 λ operates as the control channel while the remaining N channels at wavelengths N λ λ ,..., 1 constitute the multichannel of data transmission system[1-4]. Thus the proposed network model can be described as a TR FR TT CC − − − structure. It has a common control channel CC. TT means that each station has a tunable transmitter tuned at N λ λ λ ,..., , 1 0 . The outcoming traffic from a station is connected to one input of the passive star coupler. Additionally, every station also uses a fixed tuned receiver FR for the control channel and one tunable receiver to any of data channel N λ λ ,..., 1 indicated by TR . The incoming traffic to a user station is splitted into 1 + N wavelengths by a WDMA splitter from which one of N wavelengths can be selected by the tunable receiver as Figure 1 indicates. The transmission time of a fixed size control packet is used as time unit (control slot) and the data packet transmission normalized in control slot time units is ) 1 ( > L L which is called data slot. We assume the existence of a common clock, obtained by distributing a clock to all stations. The roundtrip propagation time between any station to the hub of the star coupler and to any other station is assumed to be equal to R time units . The roundtrip propagation plays a key role in the performance evaluation of the WDMA protocols. Most of the studies consider data packet transmission time is much greater than propagation delay. However in optical networks, propagation delay in most cases is higher than data packet transmission time. For example lets say a network with diameter 2Km and data packets with size 800 bits. In case of a channel with capacity 10 Mb/s and propagation speed of 8 10 2× , the propagation delay is 10μsec while the data transmission time is 800μsec. In case of a wavelength with capacity of 1 Gbit/sec the data transmission time is 8μsec. The close relation and the small difference between propagation delay and data packet transmission time is a very important factor in designed multiple access WDM networks.