**1.2.2 Optical integrative switching**

With the increasing of data traffic and the growing diversity of services, several optical network paradigms for future internet backbone have been under intensive research . Wavelength division multiplexing (WDM) appears to be the solution of choice for providing a faster networking infrastructure that can meet the explosive growth of the Internet. Since this growth is mainly fueled by IP data traffic, wavelength-routed optical networks employing circuit switching which is also called optical circuit switching (OCS) may not be the most appropriate for the emerging optical Internet. OCS is lack of flexibility to cope with the fluctuating traffic and the changing link status. Optical packet switching (OPS) is an alternative technology that appears to be the optimum choice. The OPS requires the technologies such as optical buffer and optical logic which is not mature enough to provide a viable solution.

Optical burst switching (OBS) represents a balance between optical circuit switching and optical packet switching that combines the best features of both. A comparison of optical burst switching approaches shows that OBS delivers a high-bandwidth utilization, cost efficiencies and good adaptivity to congestion while avoiding OPS' s implementation difficulties such as high processing and synchronization overhead and the need for too immature optical buffer memory. OBS delivers a high-bandwidth utilization and it is much agile than the OCS. While OBS is not good at transmitting circuit switching services.

Optical Integrative Switching (OIS) networks technology can agilely support the multiservices[l IEEE Std 802.16e] in WIMAX. In OIS ring networks technology supporting WiMAX, four different classes of service traffic are considered. The O class of traffic (Class 0) can support Unsolicited Grant Service (type 0) in WiMAX; The class 1 traffic can support Real-Time Variable Rate Service (type 1) and Extended Real-Time Variable Rate Service (type 4) in WiMAX; The class 2 traffic can support Non-Real-Time Variable Rate service (type 2) in WiMAX; The class 3 traffic can support Best Efforts Service (type 3) in WiMAX. For service flows, the class parameter should be used when determining precedence in request service and the lower numbers indicate higher priority.
