it number or a 7-digit number will work for a local call. However, if the subscriber leaves his or her home area code, then the subscriber must use 10-digit dialing for all calls, including both calls to the home area code and calls to the area code where the subscriber is currently registered as a visitor. A subscriber can work around this limi- tation by using the cellular telephone's capacity to use 10-digit dialing even in the home area code. If all numbers are dialed with 10 digits, then the subscriber dials all num- bers the same way anywhere on the North American network. 10 The MIN originally was designed to contain a North American directory number, the sub- scriber's mobile telephone number. In the worldwide wireless telephone environment, the MIN and the mobile directory number (MDN) are separate entities that are often set to the same num- 11The telephone world is moving toward more sophisticated signaling, and calls may be routed directly to the serving MSC. 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 The PSTN and Telephone Switching 11.4.3.4 Roaming support for PCS. The PCS standard intends to change the goal of telephony from being point-to-point communications to being person-to-person com- munications. PCS services, and the equivalent custom calling landline services, de- mand new and different management functions in switching systems.1 12 Call forwarding requires the switch to store an alternate phone number entered by the user and to provide that number as the destination number for incoming calls. Three-way calling requires that the single radio link be connected simultaneously with two other PSTN-to-caller connections and that the addition and departure of callers be managed. Call waiting requires the handling of two simultaneous calls and the switch- ing between those calls. Caller 