tailieunhanh - Optical Networks: A Practical Perspective - Part 6

Optical Networks: A Practical Perspective - Part 6. 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. | 20 Introduction to Optical Networks Figure An IP over SONET network a The network has IP switches with SONET adaptors that are connected to a SONET network b The layered view of this network. Network Data link Network Data link Physical b Figure The layered view of an IP over ATM over SONET network. Another example of this sort of layering arises in the context of an IP over ATM over SONET network. Some service providers are deploying an ATM network operating over a SONET infrastructure to provide services for IP users. In such a network IP packets are converted to ATM cells at the periphery of the network. The ATM switches are connected through a SONET infrastructure. The layered view of such a network is shown in Figure . Again the IP network treats the ATM network as its link layer and the ATM network uses SONET as its link layer. The introduction of second-generation optical networks adds yet another layer to the protocol hierarchy the so-called optical layer. The optical layer is a server layer The Optical Layer 21 Figure A layered view of a network consisting of a second-generation optical network layer that supports a variety of client layers above it. that provides services to other client layers. This optical layer provides lightpaths to a variety of client layers as shown in Figure . Examples of client layers residing above a second-generation optical network layer include IP ATM and SONET SDH as well as other possible protocols such as Gigabit Ethernet ESCON enterprise serial connection a protocol used to interconnect computers to storage devices and other computers or Fibre Channel which performs the same function as ESCON at higher speeds . As second-generation optical networks evolve they may provide other services besides lightpaths such as packet-switched virtual circuit or datagram services. These services may directly interface with user applications as shown in Figure . Several other layer combinations are possible and