led 611 over the same ATM network. As a result, the majority of For example, if a company has offices in Atlanta and San Antonio and an employee in Atlanta makes a call to a destination in the local San Antonio area, this call can be routed over the inter- nal network from the Atlanta PBX to the San Antonio PBX and then routed from the San Antonio PBX to the local exchange of the PSTN, eliminating long distance charges for the call. 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. Hybrid Voice-Data Networks Hybrid Voice-Data Networks customer-service calls from its own subscribers nationwide reached the call center without incurring any long-distance charges. The ATM network handled these voice calls whenever it had the capacity to do SO. If the ATM network was at capacity, the cus- tomer calls were routed to the PSTN. The result was a significant reduction in the cor- poration's monthly long-distance bill with no loss of call quality. ATM would seem like an ideal solution to the problem of optimizing capacity, and it is, up to a point. The limitation arises when the network nears capacity. ATM, as cur- rently implemented, has two shortfalls that can be improved on in future standards. The first area for improvement is in the arena of managing QoS within the call path. Although the network knows the QoS class requested for each cell of data, it does not have advanced alternate routing capability within the network. Standards and systems are under development to provide better management in situations in which bottle- necks could occur. Some of these improve ATM, and others operate with new services that compete with ATM. ATM performance will improve as two specific issues are ad- dressed. The first is an improved ability to create virtual circuits providing QoS spe- cific to time-sensitive service, and the second is the ability to adjust dyna