TAILIEUCHUNG - Optical Networks: A Practical Perspective - Part 60

Optical Networks: A Practical Perspective - Part 60. This book describes a revolution within a revolution, the opening up of the capacity of the now-familiar optical fiber to carry more messages, handle a wider variety of transmission types, and provide improved reliabilities and ease of use. In many places where fiber has been installed simply as a better form of copper, even the gigabit capacities that result have not proved adequate to keep up with the demand. The inborn human voracity for more and more bandwidth, plus the growing realization that there are other flexibilities to be had by imaginative use of the fiber, have led people. | 560 Network Survivability 104 Why Optical Layer Protection The optical layer provides lightpaths for use by its client layers such as the SONET IP or ATM layers. Recall that the layers that use the services provided by the optical layer are called client layers of the optical layer. We have seen that extensive protection mechanisms are available in the SONET layer and there is some degree of protection possible in the other client layers as well. These layers were all designed to work independently of each other and not rely on protection mechanisms available in other layers. We will see below that there is a strong need for protection in the optical layer despite the existence of protection mechanisms in the client layers. SONET SDH networks incorporate extensive protection functions. Elowever other networks such as IP ATM and ESCON networks do not provide the same level of protection. As we saw in Section IP traffic for the most part is best-effort traffic. However as carrier networks become more data centric there is an increasing expectation from both carriers and their customers that these networks will need to provide the same level of availability as SONET and SDH networks. One way for realizing this capability is to develop additional protection mechanisms within the IP ATM or other client layers as we saw in Section . Another way to protect data networks is to rely on optical layer protection which can be quite cost-effective and efficient. Significant cost savings can be realized by making use of optical layer protection instead of client layer protection. We illustrate this with two examples. Consider an example of a WDM ring network with lightpaths carrying higher-layer traffic. Figure illustrates an example where there is no optical layer protection. Two SONET line terminals LTEs are connected to each other through lightpaths provided by the optical layer as are two IP routers. For simplicity we look at a undirectional lightpath from LTE

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