ystem when it is not the home system. Automatic routing of roamer incoming calls relies on the user terminal location data in the HLR and that the user terminal is in the active state. For the duration of call completion, the user terminal is assigned a temporary local directory number (TLDN). A subscriber can disable the automatic call delivery feature. Here is a typical call delivery scenario: The originating MSC queries the HLR about the subscriber status. The HLR sends a route request to the serving MSC. The serving MSC allocates a TLDN to the user terminal. The serving MSC tells the HLR the TLDN. The HLR tells the originating MSC the TLDN. The originating MSC routes the call to the TLDN. The serving MSC associates the TLDN with the user terminal. The serving MSC pages the user terminal. The user terminal responds to the page. The radio link is created for the call. The serving MSC sends an alert message. The call proceeds normally. 15.3 Short Message Service (SMS) Wireless telephone subscribers and PSTN subscribers sending pages and similar mes- sages use short message service (SMS) to send messages of one or two sentences to an- other SMS subscriber. The SMS subscribers do not have to be wireless, but the service certainly seems to be concentrated in the wireless community. 15.3.1 Short message entities A short message entity (SME) is anything capable of originating and receiving a short message using SMS. An SME may be in a fixed network outside the ANSI-41 network, 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 or an SME may be within the ANSI-41 network, typically a mobile terminal. It should be able to Compose short messages. Send short messages. Receive short messages. Store received short messages. Manage stored short messages. Display short messages. Request supplementary services. ANSI-41 does no