Routing and Wavelength Assignment OTDM/WDM Networks with Physical Impairments

In this paper we evaluate the impact that physical impairments have on the resource consumption in Wavelength Division Multiplexing (WDM) networks where bandwidth utilization is optimized performing an Optical Time Division Multiplexing (OTDM). In particular we propose two modified heuristics to solve the problem of Routing and Wavelength Assignment (RWA) in OTDM/WDM networks where physical impairments are taken into account. In literature this RWA problem is referred to as S-RWA (Super- Lightpath RWA) because Super-Lightpath must be routed. If D is the OTDM multiplexing degree, a Super-Lightpath is able to carry all connections from a single source node to D different destinations using the D time-slot carried out on each wavelength. The effectiveness of the technique is evaluated on the COST 266 physical topology and when random logical topologies with several connectivity degrees are considered. The RWA problem under physical impairments has been solved versus D and . The resource consumption is characterized by the average number n of wavelengths used and the number nSL of Super-Lightpath routed. When a heuristic optimizing the number of links occupied for each Super-Lightpath is used, we have obtained for D==16 (n, nSL)=(24.3, 26) and (n, nSL)=(18.9, 145) when an S-RWA problem with and without physical impairments is solved respectively. The increase in number of Super-Lightpath was expected because the routing with physical impairments leads to shorter Super-Lightpath so much more of them are needed to solve S-RWA problem. On the contrary the lower number of wavelengths is explained with a better distribution of the Super-Lightpaths on physical topology when physical impairments are taken into account. In fact when they are not considered, Super- Lightpaths are longer, it is more probable that two Super-Lightpaths have at least one link in common and so a greater number of wavelengths are needed.