 cell-a rather significant price to pay, particu- larly when other technologies such as IP and SONET add their own sig- nificant percentages of overhead to the overall payload. This reality is part of the problem: ATM's original claims to fame, and the reasons it rocketed to the top of the technology hit parade, were its ability to switch cells at tremendous speed through the fabric of the wide-area network and the ease with which the technology could be scaled to fit any network situation. Today, however, given the availability of high-speed IP routers that routinely route packets at terabit rates, ATM's advantages have begun to pale to a certain degree. ATM Evolution ATM has, however, emerged from the flames in other ways. Today, many service providers see ATM as an ideal aggregation technology for diverse traffic streams that need to be combined for transport across a WAN that will most likely be IP-based. ATM devices, then, will be placed at the edge of the network, where they will collect traffic for transport across the Internet or (more likely) a privately owned IP network. Furthermore, because it has the ability to be something of a chameleon by delivering diverse services across a common network fabric, it is further guaranteed a seat at the technology game. 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. Transport Technologies Transport Technologies It is interesting to note that the traditional, legacy telecommunica- tions network comprises two principal "regions" that can be clearly dis- tinguished from each other: the network itself, which provides switching, signaling, and transport for traffic generated by customer applications, and the access loop, which provides the connectivity between the cus- tomer's applications and the network. In this model, the network is con- sidered to be a relatively intelligent medium, while the c