 explained in Sec. 23.3, the traffic engineering of packet data is based on what amount of delay is considered too long and how often we can tolerate delays over the limit. In Sec. 37.2.2 we went over a nested-delay approach that enables the MSC-to- PPDN packet data link to have enough speed and capacity for each category of data de- lay tolerance. It is important to evaluate the mix of data services and to engineer the packet data link so that each level of delay receives adequate QoS. The same half-second hiccup that looks really lame on a real-time video link is unlikely to be noticed by a computer user. And the 15-second pause that would annoy a Web surfer is not going to bother somebody waiting for e-mail. Each level has its own requirements, and we can engineer the packet data pipe to meet those individual requirement without buying more ca- pacity than we need. Our ability to engineer QoS on packet pipes will grow as new stan- dards and technologies for managing QoS on packet pipes and networks are deployed. 44.5 Conclusion We add transport to our cellular network to keep up with growth and with changes in usage of different types of service, and we modify our backhaul network to reduce cost; these are routine, mundane activities, especially in parts of the world where the PSTN provides a solid backbone. The routine nature of the work should not make us think that the work is of low value; the opposite is true. Continually maintaining quality and lowering cost is the basis for increased net revenue. This increases our network's growth potential both by providing financial resources for growth and also providing robust network that is easier to modify with new technology. 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. Adding Transport Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyrig