picking up messages from his or her own cellular phone. Digits also can be entered during the nonquiet part of the call, but then there will be Touch Tone sounds on the line. 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. Call States Call States Call Waiting End or Hang Up TALK 1 RINGING TALK 2 End or Hang Up QUIET TALKING They Disconnect Digits Digits CALLING QUIET 2 Digits CALL 2 TALK 3 Connect End or Hang Up End or Hang Up End or Hang Up Three-Way Calling Figure 16.6 Wireless states with call waiting and three-way calling. 16.4 Wireless Radio States In the same way that call feature designers use state diagrams to work out the flow of a telephone call, radio technology designers use similar state diagrams to work out the air interface. A high-level view of the wireless call setup is shown in Fig. 16.7. The user terminal is turned on and sends its registration message. The wireless system accepts the message and acknowledges the registration. The user terminal is now ready to make and receive calls. Three things can happen to a registered wireless telephone, a call can come in, the subscriber can make a call, or the subscriber can turn it off. Once the user terminal re- ceives a page, it establishes a connection with the system the same way it does when initiating a call. Radio link parameters are established, and a voice link is established. This state diagram is a picture of what happens when things go right. It does not show all the alternative pathways where things go wrong. Some of those alternatives are explained clearly in technology specifications, whereas others are left up to Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Anv use is subject to the Terms of Use as given at the website Call States Key Telephony Concepts 