tremendous amount of packet traffic on the public packet data network (PPDN), and there is a significant traf- fic engineering job to be done managing the Internet. However, DSL itself is an access technology. Most of us with DSL service were given some new terminal equipment, some junction boxes on the side of the house, and a DSL modem, but the service itself is provided on the existing loop to the telephone company switch. DSL installation is an access provisioning issue but not a traffic engineering issue. 7We say effectively here rather than efficiently because having 10 percent of the calls using 2 links may not be considered more efficient, but having 8 links instead of 10 for the same level of service is certainly more effective. 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. Traffic Engineering for Voice and Data Traffic Engineering for Voice and Data The advent of DSL did, however, solve a traffic engineering problem. In the late 1990s, the PSTN suddenly and unexpectedly encountered capacity problems. The prob- lems were created not so much by having more calls but by the fact that with so many people browsing the World Wide Web via modem, calls were lasting much longer, on av- erage, than ever before. Traffic engineering assumptions about the average length of calls, which had been accurate for decades, simply were no longer true. Parts of the PSTN, in California and elsewhere, were clogged with local calls. Capacity was being exceeded, blocking rates were too high, and because the calls generally were made on unlimited local service, no revenue was being realized. Offering DSL mitigates the problem in two ways. The users who most want a lot of time on the Internet switch to DSL at about $50 per month. This increases the local ac- cess provider's revenue. The DSL data are routed outside the PSTN by a device at the local exchange 