0 ANSI-41 bytes. However, SMS uses at least four ANSI-41 messages over the SS7 network for each short message of 160 bytes or less, and the short message itself is on separate switches and data links, not on voice channels. This means that a surge in SMS use will make major demands on the SS7 network without using any voice circuits (real or virtual) or data circuits. Also, SMS messages will increase the demand on switching capacity while requiring very lit- tle air-interface capacity, unlike voice calls and data services, which require a much higher proportion of air-interface capacity than signaling capacity. 25.5 Other Signaling Activity There are many other parts to ANSI-41. There is user terminal authentication to pre- vent wireless telephone fraud. There is over-the-air service provisioning (OTASP) SO that subscribers can sign up for service and change their feature lists over the radio link. System technicians use ANSI-41 messages to change the status of facilities for op- erations, administration, and maintenance (OA&M). 20ne SMS message-routing model we analyzed indicated that, for some calls, there might be two SMSCs involved. If these methods are used, then two or four more routing messages would be added to the overhead for each SMS message. 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 Signaling Capacity Capacity and Quality Principles These are all important ANSI-41 functions, but these are not heavy hitters in terms of message quantity. The authentication process is part of user terminal registration, we suspect that few subscribers make frequent service changes, and facilities should not need to go out of service for testing very often. 25.6 Adding It All Up Once we have estimated all the significant contributions to the ANSI-41 signaling load, we have to add them up. Each handoff, roaming, call-processing, and SMS 