m) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Introduction to GSM Introduction to GSM Teleservices Bearer services Supplementary services Teleservices The most basic teleservice supported by GSM is telephony, the transmission of speech. It has an added emergency service, where the nearest emergency service provider is notified by dialing three digits. The emergency number 112 is used like 911 in North America. Group 3 fax, an analog method described in ITU-T recommendation T.30, is also supported with the use of an appropriate fax adapter. A unique feature of GSM compared to older analog systems is the Short Message Service (SMS). SMS is a bidirectional service for sending short alphanumeric (up to 160 bytes) messages in a store-and-forward fashion. For point-to-point SMS, a message can be sent to another subscriber to the service, and an acknowledgement of receipt is provided to the sender. SMS can also be used in a cell broadcast mode for sending messages such as traf- fic updates or news updates. Messages can be stored in the Subscriber Iden- tity Module (SIM) card for later retrieval. The SMS service has been very well accepted with over 1 billion SMS messages being sent monthly. As things progressed, Phase II of GSM introduced enhancements. For example, in the teleservices, half-rate voice coding was introduced. In the first phase, full-rate voice coding was used at a rate of 13 Kbps for a voice conversation. Later, the 6.5-Kbps vocoders were introduced for use at a net- work operator's choice. This enables the network operator to offer good speech quality to twice as many users without any additional radio resources. Essentially, we split the channel in half, because people actually carry traffic on the channel only 25 to 30 percent of the time. Enhancements also included better SMS informational flow for point-to- point communications and the use of point-to-multipoint communications. The 160-character SMS message was fin