services Other telecom services Services have been classified by the CCITT as in Figure 11.16 (CCITT, 1988; Wright and To, 1990). The two major groupings are Figure 11.14 Service trends interactive services, where transmission is in both direction, and distribution services, where transaction is in one direction only at any time. Services Interactive Distribution Conversational Messaging Retrieval Without user With user presentation control presentation control Voice Voice mail Voice mail Electronic mail Weather forecast Facsimile Facsimile Facsimile Radio Stock prices Video surveillance Video mail Video Travel news Video conference Hi Fi Video phone Figure 11.16 CCITT grouping of services 11/18 The telecommunications industry Interactive services can be further subdivided into conversational, Gilhooly, D. (1990) A look at the arbiters of change, Commun. Week messaging and retrieval. Conversational services usually apply to Internat., 12 November. small user groups and require low end to end delays, and relatively Huber, R. (1991) Europe's IBC Strategy, Communications Interna- high bandwidth. Since a human operator is involved accuracy (i.e. tional, October. low loss) is usually less important since it can be compensated for. ITU (1986) Girmaw, I. and Morman, E.: Investing in Telecommuni- Examples of interactive conversational services are voice conversa- cations, Geneva, October. tion and videoconferencing. ITU (1988a) Centre for Telecommunications Development, De- Interactive messaging services are similar to conversational ser- cember. vices except that only the 'send' part of the action is carried out, the ITU (1988b) Telecommunications and the national economy: A 'retrieval' being considered to be part of a separate service. quantitative study using a macroeconomic cross-sectional ana- Examples are logging of voice onto a voice mail system, sending lysis, Geneva, May. electronic mail, and sending a facsimile message. In this service Kaplan, G. (1990) EC '92: status report, IEEE Spectrum, June. accuracy is im