TAILIEUCHUNG - Optical Networks: A Practical Perspective - Part 74

Optical Networks: A Practical Perspective - Part 74. 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. | 700 Deployment Considerations These networks are sometimes called storage-area networks. This is the primary application for most of the WDM networks deployed in metro networks today. Because of the nature of the traffic and a large amount of passthrough traffic in these networks a strong case can be made for deploying WDM rings with optical add drop multiplexers instead of higher-speed TDM rings. We present a detailed case study of a metro access network in Section . It is important to realize that despite the shorter spans for metro networks optical amplifiers may still be needed for several reasons 1. Although spans are short in many cases the fiber in the ground is old has many connectors in its path and thus has relatively high loss. For example a 10 km metro link may have a loss as high as 10 dB. 2. The loss is not just due to spans a large component of the loss comes from the loss of optical add drop multiplexers each of which can add several decibels of loss. 3. Finally protection requirements drive the need for alternate spans that may be much longer for example around a ring than the working spans. As of this writing there has been widespread deployment of private WDM links for enterprise applications in the metro network. Several carriers in the United States have deployed WDM in their metro networks but many are still considering the relative benefits of WDM versus other alternatives in this part of the network. As such the deployment is not yet as ubiquitous as it is in the long-haul network. Metro Ring Case Study We now look at a detailed example of upgrading a metro ring based on a study done in GR99 . Consider a four-node access ring with three remote nodes homing into a hub node. Assume for simplicity that all traffic is between the hub node and the remote nodes with no traffic between the remote nodes themselves. Initially we have a SONET ring operating at OC-3 155 Mb s capacity. Suppose the capacity on this ring is exhausted and that

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