-41E network reference model. 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 turned on. This makes sales much easier because it makes it easy for untrained sales staff at third-party vendors to sell the cellular telephone with service without having to know how to set up the service. The OTASP function communicates with the MSC over the unspecified N1 interface, with the VLR over the unspecified D1 interface, and with a customer service center (CSC) over the unspecified X interface. There are seven roles defined in ANSI-41 for the MSC during the call process. An MSC will have one or more of these roles in relation to each call during each moment of call setup, call operation, and call takedown: Home is the MSC with the subscriber's HLR. Serving is the MSC with the base station and radio link. Anchor is the MSC that was serving at the beginning of the call. Tandem is an MSC, not the first or last, in the handoff chain. Target is the MSC where we want to hand off. Originating is where the subscriber's telephone number is. Gateway is an originating MSC that is not the home. The gateway MSC function occurs with mobile-originated calls if the call is made while the cellular telephone is roaming. Now we have all the circles and arrow in place for ANSI-41, but we have not talked about what it does for us. ANSI-41 defines the processes that allow for handoffs, path minimization, short message service (SMS), and operations, administration, and main- tenance (OA&M). We will discuss each of these in turn. 15.1 Inter-MSC Handoffs Intersystem handoff allows a wireless telephone call to hand off from one MSC to an- other. There are five distinct functions in ANSI-41 handoff support: Handoff measurement Handoff forward Handoff back Path minimization Call release For any of this to work, the MSCs must have their cell identification scheme c