In the OBS network concept, a collection of optical burst switched are interconnected with WDM link to form the central core of the network. Devices called edge routers collect traffic flows form various sources at the periphery of a WDM network, as illustrated in Fig 13.36. The flows then are sorted into different classes according to their destination address and grouped in variable-sized elementary switching units called burst. The characteristics of an edge router play a critical role in an OBS system since the overall network performance depends on how a burst is assembled based on particular types of traffic statistics.