Performance of a packet switched WDM network with dynamic wavelength selection

WDM networks in general depend on transmitters and receivers that are precisely tuned to predetermined fmed wavelengths. Robust WDM is an approach aimed at relaxing manujkcturing and operating wavelength tolerance requirements, which will lead to cost effective implementations. In this approach, connections are based on dynamically selected wavelengths as opposed to usingfied wavei'ength channels. A station that needs a connection selecfs a wavelength during a reservation interval. The perjormance of a simplified WDM protocol with dynamic wavelength selection is modeled and analyzed for packet traffic. In this version, the reJewation intervals are assigned to stations randomly. The pegormance of the protocol is analyzed for different network parameters. 1. Introductiorc The research on fiber optic networks is driven by new emerging applications and services [S I such as networking full-mcltion color-graphics workstations and applications involving medical imaging. There is also a need for hgh-speed interconnection of supercomputers, LANs and MANS with those applications. The fiber optic technology provides the necessary high bandwidth medium for such applications. The single-mode optical fiber has presented the exciting dilemma of a transmission medium which has a bandwidth of several TI%, that exceeds both the speeds at which it can be accessed by conventional means and the aggregate information rates for which it is likely to be used [3]. Since the maximum rate at which each user can access the network is lirmted by the electronic speed (to few gigabits per second), the key in designing lightwave networks in order to exploit the huge bandwidth is to introduce concurrency among multiple-user transmissions into the network architectures and protocols. In alloptical networks, concurrency may be provided by either wavelength or frequency (wavelength division multiple access WDMA) [,4,6,14], time slots (time division multiple access TDMA) [8], or wave shape (code division multiple access CDMA) [ 161. The basic need of all-optical TDMA and CDMA to have nodes synchronized to within one time slot (for TDMA) and one chip time (for CDMA) make them less attractive than WDMA. On the other hand, WDMA employs mostly existing technologies associated with intensitymodulation direct-detection systems. Also, WDMA is the current favorite since a l l of the end-user equipments need operate only at the bit rate of a wavelength division multiplex (WDM) channel. in WDM, the vast ba.ndwidth of the fiber medium is divided into many dlifferent channels, each of which corresponds to a different wavelength (or frequency), wherein the bandwidth of each channel is limited by the operating capacities of the end resources [4]. Multiple connections can be present at the same time, as long as they are on d ~ e r e n t wavdengths. The minimum channel spacing is limited by crosstalk. The spacing between channels can be reduced if the end-user transmitters (lasers) "e of good quality, i.e., they are stable and do not drift too far from their nominal operating wavelength range. WDM requires narrow spectral-width lasers and optical filters to distinguish between the different wavelengths. With the use of narrow-band lasers such as distributed feedback (DFB) and distributed Bragg reflector (DBR) lasers., a channel spacing of 1 nm or less has been demonstrate'd [ 3,141. Depending on the network architecture, the receivers are used differently. In broadcast-and-select networks [lS], each station is provided with a small number (e.g., * This material is based upon work supported in part by the National Science Foundation under Grant No. ECS9412944, and a Grant from the DOD Advanced Research Projects Agency (ARPA) Micro Electronics Technology Office (MTO), monitored by the Army Research Lab(AKL). 0742-1303/95 $4.00