the capacity of the air interface in ways we have not foreseen. The same management issue would be relevant in that case as well. 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. Quality of Service (QoS) Key Data Concepts service providers will realize a significant cost savings if they can entice subscribers to upgrade to cdma2000 user terminals. 5 However, the service provider has no way to con- trol those numbers directly. If it turns out to be the case that needing to support large numbers of cdmaOne users reduces QoS or capacity significantly, cellular service providers will have some options. The service providers could provide free upgrades or even upgrades with bonuses to subscribers with cdmaOne equipment. Or the service providers could lobby governments for the allocation of new bandwidth to be used for 3G services only. 17.3 Latency, Jitter, and Loss There are three kinds of impairments in a data system: latency, jitter, and loss. Like the noise, interference, and distortion of an analog signal, these three interact with each other in contributing to a level of service for a subscriber. The latency of data transport, or the delay in more casual usage, is simply how long it takes the data to get somewhere. We can think of a data connection as having an end- to-end latency performance, and we can think of each stage as having its own latency. The transport links used in the data connection have some latency because it takes some nonzero amount of time for the bits to get from one end to the other. A transmit- ter is in one place, a receiver is in another place, and information does not travel faster than the speed of light. However, there is another source of latency in the tandem nodes along the way. While circuit-switched data take some time to get from input to output inside a circuit switch or cross-connect, packet data are much 