detail later in the book. Transport technologies within the network cloud fall into two cate- gories: fixed transport and switched transport. Fixed transport, some- times called private line or dedicated facilities, includes such technologies as T1, E1, DS3, SONET, SDH, dedicated optical channels, and microwave. Switched transport technologies include modem-based telephone transport, X.25 packet switching, frame relay, switched Ether- net, and asynchronous transfer mode (ATM). Together with the access technologies described previously and customer premises technologies such as Ethernet, transport technologies offer the infrastructure compo- nents required to craft an end-to-end solution for the transport of cus- tomer information. The Many Flavors of Transport Over the last few years the network has been functionally segmented into a collection of loosely defined "regions" that define unique service types. These include the local area (sometimes referred to as the premises region), the metropolitan area, and the wide area (sometimes Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. First Things First First Things First known as the core). Local area networking has historically defined a net- work that provides services to an office, a building, or even a campus. Metro networks generally provide connectivity within a city, particularly to multiple physical locations of the same company. They are usually deployed across a ring architecture. Wide area networks, often called core transport, provide long-distance transport and are typically deployed using a mesh networking model. Transport Channels The physical circuit over which customer traffic is transported in a net- work is often referred to as a facility. Facilities are characterized by a number of qualities such as distance, quality (signal level, noise, and dis- tortion coefficients), and b