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Chapter 9. Optical Network Survivability > Why Optical Layer Protection

9.4. 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. However, other networks such as IP, ATM, and ESCON networks do not provide the same level of protection. As we saw in Section 9.3, 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 9.3. 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.


  

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