bps for basic speech service and limited data rates up to 32 kbps 64 kbps for speech and data, with the possibility of simultaneous speech and data 144 kbps for videotelephony and other data services 384 kbps for more data services, including advanced packet data 768 kbps as an intermediate step between 384 kbps and 2 Mbps 2 Mbps is the state of the art and is defined for the forward direction only We will discuss the four quality-of-service (QoS) classes in W-CDMA: conversational, streaming, interactive, and background. Delay sensitivity is the main distinction among these W-CDMA QoS levels. 10.3.1.1 Conversational class. Conversational class is mostly circuit-switched voice, but voice over IP (VoIP) and videotelephony are expected to require this type of service. This is meant for communication between live human beings. The traffic is symmetric in character, and the end-to-end delay must remain low. Human perceptions define the requirements of the W-CDMA conversational class of service, and people seem to allow 400 ms of end-to-end delay before the channel starts to annoy them. End-to-end delay is from the caller's mouth to the called party's ear, so delays created during encoding and decoding in the user terminals must be included, as well as propagation and circuit delays. Circuit-switched voice is old-fashioned telephone service, with the same voice qual- ity as 2G GSM when radio conditions permit. Unlike cdmaOne and cdma2000, the 10 Note that although the United States has a reputation for arrogance, it is the European tele- phony community that has declared its systems first global and now universal. GSM is operating on several continents but is far from global. The authors' research indicates that no cellular system is likely to go beyond global, extending past earth's biosphere to the larger universe, any time soon. 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