oordi- nated SO that each MSC knows where the neighbors are for its own cells. Intersystem handoff requires dedicated transport facilities from MSC to MSC, as well as the ANSI- 41 E interface links. The length of the handoff chain on these dedicated facilities is re- duced by using the handoff-back operation and by path minimization and ultimately is limited by parameters set by the wireless service providers. In this section we speak about MSCs signaling to user terminals and MSCs detect- ing user terminal behavior. Of course, this signaling and detection go through an air interface, a base station, and a base-station-to-MSC signaling link. For the purpose of 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 Key Telephony Concepts this discussion, we can treat these three steps as intermediate links in a communica- tion chain. Also, we refer to a user terminal as changing to a new channel in the hand- off process. In CDMA, it may be a different pseudonoise (PN) code on the same radio frequency. According to the latest papers available at the time of publication, ANSI-41 does appear to specify inter-MSC soft handoff, but some vendors, including Lucent Tech- nologies, do support inter-MSC soft handoff within their own equipment. 15.1.1 Handoff measurement In an intersystem handoff, we have a serving MSC and a target MSC where we are con- sidering a handoff. As in the single-system handoff case, the CDMA user terminal pro- vides measurements to the serving base station. For base station measurements, the serving MSC designates candidate MSCs and sends handoff measurement request messages to them. The candidate MSC may not respond if it cannot support the radio channel charac- teristics of the call, if it does not detect a strong enough radio signal to measure, or if its own traffic conditions render it unavailable for a handoff. This is a