 port reserved for data devices. Upon arrival at the CO, the data traffic does not travel to the local switch; instead, it stops at the ADSL modem that has been installed at the CO end of the circuit. In this case, the device is actually a bank of modems that serves a large number of subscribers, and is known as a Digital Subscriber Line Access Multiplexer, or DSLAM (pronounced "dee-slam"). A rack of DSLAMs is shown in Figure 6-5. Instead of traveling on to the local switch, the data traffic is now passed around the switch to a router, which in turn is connected to the Internet. This process is known as a line-side redirect. The advantages of this architecture are fairly obvious. First, the redi- rect offloads the data traffic from the local switch so that it can go back to doing what it does best-switching voice traffic. Second, it creates a new line of business for the service provider. As a result of adding the router and connecting the router to the Internet, the service provider instantly becomes an ISP. This is a near-ideal combination, because it allows the service provider to become a true service provider by offering much more than simple access and transport. Figure 6-5 A bay of DSLAMs 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. Access Technologies Access Technologies As the name implies, ADSL provides two-wire asymmetric service- that is, the upstream bandwidth is different from the downstream. In the upstream direction, data rates vary from 16 to 640 Kbps, while the down- stream bandwidth varies from 1.5 to 8 Mbps. Because most applications today are asymmetric in nature, this disparity poses no problem for the average consumer of the service. A Word about the DSLAM This device has received a significant amount of attention recently because of the central role that it plays in the deployment of broadband access services. Obvi