SMSC may send the message on a designated alternate service. The alternate service might be a paging service capable of reaching a subscriber who was out of range of the mobile network. The SMSC has some other capabilities. For example, it is able to prioritize messages. If a high-priority message is received, it can be handled before low-priority messages received earlier. The SMSC is defined as a logical entity. Its physical implementation in hardware and/or software is left to the vendor. The role of the HLR was discussed earlier. It assists the message delivery process by informing the SMSC regarding the location of the destination SME. It also performs the same function for the MSC because the MSC rechecks the location of the destina- tion SME before sending the SMS message. When the MSC receives the short message, checks the current location of the destination SME with the HLR and then sends the message to the serving base station, which delivers it to the receiving SME. 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. Short Message Service (SMS) Key Data Concepts The receiving SME receives the short message. If it is a typical text message, it sig- nals the subscriber with a light, vibration, or tone depending on the device and user settings. It displays the message on screen. Usually, it also displays the name of the sender and the time the message was received at the SMSC. These may appear above or below the message. Of course, other types of messages will be handled differently by the SME. For example, control codes from the cellular service provider sent by SMS could set or reset parameters of the cellular telephone via binary SMS messages for over-the-air parameter administration (OTAPA). In addition, the receiving SME can send a status-report short message indicating receipt of the original message. This is passed back through th