t is subscriber behavior that is important enough to put on the state diagram. The QUIET, RINGING, and TALKING states for incoming calls are the same as landline states. Instead of a DIALING state, wireless calls have a CALLING state, where the system is trying to complete the dialed call. This state is distinguished by having a voice link to the subscriber with no connection to another telephone. RINGING End or Hang Up QUIET TALKING They Disconnect Digits CALLING Figure 16.5 Four-state diagram of a basic wireless telephone. 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 Key Telephony Concepts Custom calling had to be reengineered for wireless to take preorigination dialing into account. Using the SEND key for a flash was natural, but the notion of dialing digits for three-way calling has some confusion. This means that wireless call waiting is almost exactly the same as regular landline call waiting with the flash key being the SEND key. In 1981, the Advanced Mobile Phone Service (AMPS) system trial telephones had no tones associated with dialed digits because they were only used for preorigination dialing. In fact, they were deliberately made silent so that a subscriber could key in a telephone number as it was spoken (by directory assistance, for example), press END, and press SEND to make a new call. The notion of pressing buttons to send Touch Tone digits on a telephone call required the telephone design to change, and the buttons on wireless telephones have been dual-purpose ever since. The numbered buttons on a wireless telephone put digits into a register to be sent the next time the SEND key is pressed, and those same numbered buttons send Touch Tone signals when a call is in progress. Wireless three-way calling uses the same digit registers as initiating a wireless tele- phone call, so the Touch Tone sounds serve no pu