Networking Perspectives

By David Crowe SMS: Building a Pager into a Cell phone

Short Message Service (SMS) will allow alpha-paging capabilities to be built into newer cellular phones, both digital and analog. Short messages can actually be quite long (up to about 200 charac­ ters on digital phones) and can include letters, digits and punctuation. These messages can be sent to a cellular terminal or even transmitted battery life can be extended manyfold. from a cellular terminal. The main benefits of The problem with sleep mode is that when this feature are as a pager replacement, to the sleep interval gets long (e.g. over 5-10 sec- provide new text-based services and, surpris- onds), incoming callers will not want to wait ingly, to extend battery life. for the mobile to wake up. This is where SMS A simple feature based upon SMS will be will ride in to save the day. A mobile that is voice mail notification. Instead of the confus- sleeping too long to make receiving calls prac- ing beeps and alerts of today, or the voice- tical, will certainly be able to receive short channel consuming recorded reminders, the messages. This combination of capabilities SMS version of the feature will allow a text gives a phone user a useful balance between message indicating the number of un- today's two choices, to receive every heard voice mail messages waiting in David Crowe is the editor-in-chief of incoming call or to turn the phone off a mailbox. This service will provide Cellular Networking Perspectives. He and try to remember to check voice more information to consumers, re- has been involved in the mail regularly. Instead, SMS and sleep suit in less customer confusion and development of cellular network and mode can combine to provide notifi- use less of the limited radio re- switching technology for 10 years. cation within a couple of minutes of source. The service could even pro- an incoming call being redirected to vide the number of the caller, if the To contact Mr. Crowe call (403) 289- voice mail and allow the phone to be voice mail system supports calling 6609; fax (403) 289-6658; or e-mail left on for several days. This feature number identification. 71574.3157@ compuserve.com. will be most useful if the voice mail Pager emulation was a big motivation behind the de- notification does include the calling number. velopment of SMS. Cellular operators hope to be able to persuade the many cellphone subscribers that also car­ Short Messaging ry a pager around to send it back and pay for SMS in­ SMS is already available in a restricted form on nar­ stead. Other carriers may offer some SMS services for rowband analog (NAMPS) phones (conforming to TIA free as a competitive feature and to entice subscribers Interim Standard IS-88) and will be available in regular to buy more advanced SMS services. There are, howev­ analog phones that conform to the upcoming IS-91 Revi­ er, pros and cons to SMS on a cellular phone versus a sion A standard. A more advanced form of SMS is avail­ pager. On the positive side, SMS can easily offer many able on digital phones conforming to the IS-136 TDMA more features than paging; messages can be longer, text and IS-95 Revision A CDMA standards. First generation can be included in the messages, and fancy features digital phones (conforming to IS-54 Revision B) can such as one-button callback can build on the advantage support voice mail notification, but no other types of of having the 'pager' integrated in the cellular phone. short messages. The big drawback to SMS versus a pager is battery life. Cellular phones will likely be restricted to receiving While a pager can go for weeks or months on a battery, short messages for several reasons. Analog standards current cellular phones are lucky to go for an entire day. do not support mobile initiated short messages and a cellular phone handset is hardly the ideal device for en­ Sleep Mode Alternatives tering a text message. Beyond this, the standards do not The cellular industry's answer to the battery problem is adequately support interworking with the most likely "sleep mode," which will be available on new digital cellu­ destinations for a short message: fax machines, internet lar phones conforming to the recently published IS-136 e-mail, pagers and even other cellular phones using a TDMA or the 1S-95 Revision A CDMA standard. Sleep mode different air interface. is a trick borrowed from pagers. The phone and base sta­ Support in the air interfaces is important, but it will not tion will agree on a precise amount of time to sleep. The be enough to allow short message delivery when roam­ mobile will wake up after the interval has passed, make a ing. Revision C of the IS-41 intersystem operations stan­ quick check for incoming calls or messages, and then go dard, that is scheduled for publication later this year, will back to sleep again. The base will hold any incoming calls be required. This standard defines a new network node, a or messages until the short wake up interval. Since almost Message Center (MC), that will provide interworking, all circuitry can be turned off during the sleep interval, store and forward functions for short messages.

September 1995 49