 ring. 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 service area. The repeat registration can be lost or garbled, or it may be received and its acknowledgment may not be. Incoming call pages may not be received. When a system does not get a response for an in- coming call, it tries again and it may try a third time, but it has to give up eventually. caller gets a recording about the cellular subscriber being unavailable. At this point, a sub- scriber's voice-mail service may come in and take a message. When a page is received or when the subscriber presses the SEND key, the user ter- minal establishes a link with the system. Several messages go back and forth, includ- ing dialed digits for wireless originations, and any of these can be missed or garbled. These messages have been designed aggressively to have enough redundancy not to be misinterpreted. It is pretty safe to say that they are received correctly or not received at all. It is also pretty safe to say that the same designers made sure that such an un- likely event is handled to avoid glare conditions, as described in Sec. 23.6. The voice link can fail while the call is in progress. Not only may the user terminal be moved into a poor coverage zone, but it may be shut off midcall. Back in the car- phone days before user terminals had battery power, it was common to park the car while talking on the telephone, to follow the usual routine, to shut off the ignition, and oops, to lose the call. Even today, however, batteries can go dead during a call, or users can drop the telephone, causing the battery to pop off. This is just the highest-level overview of wireless call setup; each of these states can be divided into a more detailed view of the process. Much of this detail is described in specifications, but quite a bit is left to the individual equipment desi