or train station, then we expect it to perform dif- ferently than an MSC region serving mostly shopping malls. The roamer signaling es- timate is a total of the signaling needs for roamers from other wireless telephone sys- tems and roamers in another MSC region in their home system. 36.4 Short Message Service (SMS) Short message service (SMS) is a subscriber feature handled by the ANSI-41 signaling system. Other signaling functions are internal to the wireless telephone system, mes- sages that support subscriber activity. In the case of SMS, the subscriber's message is sent right on the signaling channels. 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. Signaling Capacity Planning Signaling Capacity Planning SMS messages are sent from the sender's serving MSC to the sender's home short message service center (SMSC). If there is a concentration of short messages, then the serving MSC sees that concentration. After a message leaves the serving MSC, the sender's home SMSC takes care of it. There are also signaling messages between the sender's SMSC and HLR. Once the message is stored safely at the sender's SMSC, the message recipient is in- volved. The recipient's HLR is contacted to see whether the receiving user terminal turned on. If the receiving user terminal is able to take the message, then the sender's SMSC sends the message to the recipient's MSC on the ANSI-41 signaling network. These functions generate signaling workload. Enhanced message service (EMS) allows subscribers to send and receive ring tones, icons, and graphics. The system uses concatenated, binary-encoded SMS messages to send these larger messages. Since EMS messages involve more data than normal SMS messages, EMS subscribers place a heavier load on the signaling system than SMS subscribers. If EMS becomes popular enough, then it can be a major component of sig- naling a