tailieunhanh - Optical Networks: A Practical Perspective - Part 5

Optical Networks: A Practical Perspective - Part 5. 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. | 10 Introduction to Optical Networks that more sophisticated techniques can be used to improve the bandwidth efficiency but usually at the cost of slower restoration times. This realization is stimulating the development of service offerings that trade off restoration time against bandwidth efficiency in the network. Thus carriers in the new world need to deploy networks that provide them with the flexibility to deliver bandwidth on demand when needed where needed with the appropriate service attributes. The where needed is significant because carriers can rarely predict the location of future traffic demands. As a result it is difficult for them to plan and build networks optimized around specific assumptions on bandwidth demands. At the same time the mix of services offered by carriers is expanding. We talked about different circuit-switched and packet-switched services earlier. What is not commonly realized is that today these services are delivered over separate overlay networks rather than a single network. Thus carriers need to operate and maintain multiple networks a very expensive proposition over time. For most networks the costs associated with operating the network over time such as maintenance provisioning of new connections upgrades far outweigh the initial cost of putting in the equipment to build the network. Carriers would thus like to migrate to maintaining a single network infrastructure that enables them to deliver multiple types of services. Optical Networks Optical networks offer the promise to solve many of the problems discussed above. In addition to providing enormous capacities in the network an optical network provides a common infrastructure over which a variety of services can be delivered. These networks are also increasingly becoming capable of delivering bandwidth in a flexible manner where and when needed. Optical fiber offers much higher bandwidth than copper cables and is less susceptible to various kinds of electromagnetic .