n implicit re- sponse that no handoff is possible here. If a candidate MSC does respond, it sends ra- dio signal strength measurements to the serving MSC. Depending on the signal strength measurements received from the candidates, the serving MSC may select a target MSC for handoff. The target MSC has to be compati- ble with the call mode, Advanced Mobile Phone Service (AMPS), CDMA, TDMA, and so on; it has to support the user terminal's power class and discontinuous transmission (DTx) modes; and it has to support whatever encryption algorithms the subscriber using. If the target MSC is already involved in this call, then a handoff back is re- quired. Otherwise, the serving MSC can try a path minimization or simply can choose to perform a handoff forward. 15.1.2 Handoff forward Once the serving and target MSCs have established that a handoff forward is appro- priate for this call, the procedure begins. The handoff chain is going to be one link longer after the handoff than before, but it must stay within the limit set by the sys- tem parameters. Here is a typical handoff-forward scenario: The serving MSC requests a handoff forward and identifies a link. The target MSC accepts the handoff forward. The source-to-target inter-MSC link is set up. The serving MSC tells the user terminal to change channel. The user terminal changes channel. The target MSC detects the user terminal on its channel. The target MSC notifies the serving MSC. The serving MSC makes the connection to the target MSC. The handoff forward is complete. 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. ANSI-41 ANSI-41 Once the handoff forward is complete, the voice channel of the user terminal is sup- ported by the new serving MSC, and the call is routed on a dedicated pipe back to the prior serving MSC, which may be the anchor MSC or a tandem MSC. 15.1.3 Handoff back During a ca