In December 2002, an invitation to lecture at the Belgacom Corporate University (Brussels) offered the opportunity to put together several years of research on the subject of short message service. The Global System for Mobile Communications (GSM) includes a large number of beautifully specified standards, with visionary ideas. Comparatively, IS-41 (the U.S.-originated mobile standard specifications for CDMA and TDMA) is much less developed. The GSM specifications are a wonderful reference but they give only a canonical description of the subject.

Short message service (SMS) is a very clever and economical resource that was designed back in the 1980s when GSM specifications were taken from CNET (the research center of France Telecom) and redeveloped as a worldwide standard. These services have been tremendously successful and multimedia messaging (MMS) will have the same success. For the same network resources as a telephone call, SMS services provide about 100 times more revenue to the operators.

I have been interested in the subject of SMS and now MMS for several years. Currently, when a telephone call is made to any number in the world, the called party is reached. For SMS, this is not yet the case by far because of a lack of connections, lack of commercial agreements, and differences in standards among GSM, IS-41 (CDMA, TDMA), and others, including Japanese standards. While developing solutions to interwork SMS and later MMS, several nonstandard (noncanonical) procedures were implemented to provide termination and two-way SMS, such as the dynamic reply path procedure.