release and sends billing information. The handoff circuits are all released. 15.2 Automatic Roaming Management of roaming is the bulk of ANSI-41 activity. Roaming management is needed every time a user terminal is activated anywhere on the system other than at the subscriber's home MSC. Intersystem handoffs are much rarer because they are only needed if the subscriber moves from one MSC serving area to another during an active call. Also, roaming is more complicated because the subscriber has to be au- thenticated and the full array of subscriber features has to be sent from the HLR to the serving system. 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 15.2.1 The HLR and VLR The home location register (HLR) is the functional entity defined in ANSI-41 that maintains subscriber information and status. In addition to being a large and power- ful database, the HLR provides control and processing-center functions. The HLR is the home database for wireless subscribers. The relatively stable information in the HLR on each subscriber includes the direc- tory number, subscribed services and features, and whether the subscriber should be offered or denied service. The more transient information is the location and call sta- tus of the user terminal. While each MSC has a separate logical HLR, a wireless service provider may opt to put several HLRs in one centralized computer. It is often more efficient to administer one large computer in one place than a collection of smaller machines at separate phys- ical locations. The visitor location register (VLR) is a database of valid roaming subscribers in an MSC region. These are subscribers who have registered, though they may never make an actual wireless call. The VLR keeps a record SO that the MSC is ready to serve them for incoming or outgoing calls. The VLR is a separate logical entity,