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Towards EÆ ient Pa ket Swit hing Metro WDM Networks Martin Maier, Martin Reisslein, and Adam Wolisz Abstra t| In this paper, we brie y overview the urrent state{of{the{art of opti al WDM networking. We thereby point out that the ubiquitous SONET/SDH{WDM metro rings are likely to be ome a serious bottlene k between high{speed lo al area networks/broadband a ess te hnologies and WDM ba kbone networks. We qui kly address innovative metro WDM network ar hite tures and formulate the requirements of future pa ket swit hing metro WDM networks. After reviewing previous work on single{hop WDM networks some learnt lessons are summarized and are used for designing a future{proof Arrayed{Waveguide Grating (AWG) based metro WDM network and a novel reservation{based Medium A ess Control (MAC) proto ol. Ea h node at the periphery of this passive single{hop WDM network is equipped with a single tunable trans eiver for data and a broadband light sour e whi h is spe trally sli ed in order to broad ast reservation requests. Ea h node has global knowledge and s hedules variable{size data pa kets in a distributed fashion by exe uting the same greedy rst{ ome{ rst{served and rst{ t arbitration algorithm. The network is reliable, s alable, and allows for opti al multi asting. All wavelengths are used for data tranmission. The proto ol supports both pa ket and ir uit swit hing. The network eÆ ien y is signi antly in reased by using multiple Free Spe tral Ranges (FSRs) of the underlying AWG, spatially reusing wavelengths, and transmitting data and ontrol simultaneously by means of spreading te hniques. Keywords| AWG, MAC proto ol, MAN, single{hop WDM networks, spe tral sli ing, spread spe trum, WDM I. Introdu tion AS ILLUSTRATED in Fig. 1, the hierar hy of ommuni ation networks an be viewed as onsisting of ba kbone, metro, and a ess networks where the latter ones olle t (distribute) data from (to) di erent lients su h as wireless stations and LANs. Let us rst onsider the ba kbone networks. Future opti al WDM ba kbone networks seem to be onverging to a two{layer infrastru ture in whi h the transport is by means of inter onne ted all{ opti al islands of transparen y while the remainder of the ommuni ation layers are based on IP [1℄. The islands of transparen y are formed out of wavelength{division multiplexing (WDM) links, stit hed together by all{opti al ross onne ts (OXCs) and add{drop multiplexers (OADMs). The opti al{ele tri al{opti al (OEO) boundaries between islands will be retained due to management, jurisdi tion, billing, and/or signal regeneration issues. Su h islands not only provide huge pipes of "in nite bandwidth" but also transparen y to data rates, modulation formats, and Inter-metro Intra-metro Intra-metro Metro Networks Access Networks / Clients wireless access (e.g., UMTS) ATM, FR, SDH, IP, GbE ESCON, Fibre Channel connections long-haul connections long-haul connections Optical WDM Backbone