doesn't matter whether the phone is corded or cordless. If cordless, pushing the TALK but- ton creates a radio link between the handset and the base station, which in turn closes the circuit. 2It's interesting to note that all-digital networks, such as those that use ISDN as the access technology, don't generate dial tone because packets don't make any noise! Instead, the ISDN signaling system (Q.931 for those of you collecting standards) transmits a "ring the phone" packet to the distant telephone. The phone itself generates the dial tone-and the ringing bell! Subout 10 years ago I took a trip to Seattle to teach a class, and my family accompanied me. One evening while strolling along Pike Street we came upon a bank of modern pay phones, all of which had dials instead of DTMF buttons. My kids, still little back then, begged me for quarters SO that they could call their friends on those cool new phones. 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. Telephony Telephony 1209 Hz 1336 Hz 1447 Hz Figure 3-10 DTMF tone pairings 697 Hz 770 Hz 852 Hz 941 Hz switch. Want to impress your friends? Try pulse dialing on a DTMF tele- phone. Simply find a phone that has a real button or buttons that you can push down to hang up the phone. Pick up the handset, then dial the number you wish to call by rapidly pushing and releasing the buttons the appropriate number of times, leaving a second or two of delay between each dialed digit. It takes a little practice but it really does work. Try something simple like Information (411) first. DTMF has been around since the 1970s, but switches are still capable of being triggered by pulse dialing. Back to our example. Cristina finishes dialing Adam's number and a digits collector in the switch receives the digits. The switch then performs a rudimentary analysis of the number to determine whether it is served out of