Optical Networks - 1_2 Services, Circuit Switching, and Packet Switch_11

Optical Networks- - 1.2 Services Circuit Switching and Packet Switching 5 Central office Home Business Long haul Interexchange network Metropolitan

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1.2 Services, Circuit Switching, and Packet Switching 5 Interexchange network Interoffice network Access network Business Home Central office Metropolitan Metropolitan Long haul Figure 1.1 Different parts of a public network. The network shown in Figure 1.1 is a terrestrial network. Optical fiber is also extensively used in undersea networks. Undersea networks can range from a few hundred kilometers in distance to several thousands of kilometers for routes that cross the Atlantic and Pacific oceans. 1.2 Services, Circuit Switching, and Packet Switching Many types of services are offered by carriers to their customers. In many cases, these are connection-oriented services in that there is the notion of a connection between two or more parties across an underlying network. The differences lie in the bandwidth of the connection and the type of underlying network with which the connection is supported, which has a significant impact on the quality-of-service guarantees offered by the carriers to their customers. Networks can also provide connectionless service; we will discuss this type of service later in this section. There are two fundamental types of underlying network infrastructures based on how traffic is multiplexed and switched inside the network: circuit-switched and packet-switched. Figure 1.2 illustrates some of the differences in the type of multiplexing used in these cases. A circuit-switched network provides circuit-switched connections to its cus- tomers. In circuit switching, a guaranteed amount of bandwidth is allocated to each connection and is available to the connection all the time, once the connection is set up. The sum of the bandwidth of all the circuits, or connections, on a link must be less
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6 Introduction to Optical Networks 121 1 22 (a) (b) 1 2 1 2 Mux Mux Figure 1.2 Different types of time division multiplexing: (a) fixed, (b) statistical. than the link bandwidth. The most common example of a circuit-switched network is the public-switched telephone network (PSTN), which provides a nailed-down connection to end users with a fixed amount of bandwidth (typically around 4 kHz) once the connection is established. This circuit is converted to a digital 64 kb/s circuit at the carrier central office. This network was designed to support voice streams and does a fine job for this application. The circuit-switched services offered by carriers today include circuits at a variety of bit rates, ranging from 64 kb/s voice circuits all the way up to several Gb/s. These connections are typically leased by a carrier to its customers and remain nailed down for fairly long periods, ranging from several days to months to years as the bandwidth on the connection goes up. These services are also called private line services. The PSTN fits into this category with one important difference—in the PSTN, users dial up and establish connections between themselves, whereas with private line services, the carrier usually sets up the connection using a management system. This situation
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This note was uploaded on 01/15/2011 for the course ECE 6543 taught by Professor Boussert during the Spring '09 term at Georgia Institute of Technology.

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Optical Networks- - 1.2 Services Circuit Switching and Packet Switching 5 Central office Home Business Long haul Interexchange network Metropolitan

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