pport and manage calls. 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. The PSTN and Telephone Switching 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. Source: CDMA CAPACITY AND QUALITY OPTIMIZATION Chapter Telephony Engineering Concepts This chapter provides an introduction to the basics of telephony for those who come from a radio engineering or data systems background, as well as for those who wish to review these fundamental concepts. The first four sections describe the key concepts of landline telephony, whereas the latter two sections introduce ideas specific to the world of cellular telephony. Telephone Call Sequence Before delving into the components and organization of a telephone network, it is worth a few paragraphs to examine the sequence of a normal landline telephone call. A land- line call starts when somebody picks up the receiver. We call this person the callING party, 1 and we say the telephone goes off-hook. The telephone network detects the off- hook condition and connects an internal resource to the line for the purpose of collect- ing the digits dialed by the caller. The telephone network then sends a dial tone to tell the callING party that the telephone network is waiting for instructions in the form of dialed digits. We call them dialed digits even though they are often dual-tone multi- frequency (DTMF) tones generated by the familiar buttons on the telephone keypad. 2 Once the callING party completes dialing a telephone number, the telephone network tries to establish a connection to the callED party through the network. If the attempt is successful, the network will both ring the phone of the callED party and locally gen- erate a ring tone t