Optical Networking Best Practices Handbook

9.4. QOS MECHANISMS

The proliferation of IP technology coupled with the vast bandwidth offered by optical WDM technology are paving the way for IP over WDM to become the primary means of transporting data across large distances with the next-generation Internet (Internet 2). WDM is an optical multiplexing technique that allows better exploitation of the fiber capacity by simultaneously transmitting data packets over multiple frequencies or wavelengths. The tremendous bandwidth offered by WDM promises reduction in the cost of core network equipment and simplification of bandwidth management. However, the problem of providing QoS guarantees for several advanced services, such as transport of real-time packet voice and video, remains largely unsolved for optical backbones. The QoS problem in optical WDM networks has several fundamental differences from QoS methods in electronic routers and switches. One major difference is the absence of the concept of packet queues in WDM devices, beyond the number of packets that can be buffered (while in flight) in fiber delay lines (FDLs). FDLs are long fiber lines used to delay the optical signal for a particular period of time. As an alternative to queuing, optical networks used additional signaling to reserve bandwidth on a path ahead of the arrival of optically switched data [4].

Over the past decade, a significant amount of work has been dedicated to the issue of providing QoS in non-WDM IP networks. Basic IP assumes a best-effort service ...