ITU-T E.131 PDF

General

Many Administrations are planning to introduce supplementary telephone services which are likely to be viable only if controlled by the user (a list of possible supplementary telephone services is given in Supplement No. 1 at the end of this fascicle). It is therefore necessary to consider means of providing users with procedures by which such control can be achieved. The purpose of this Recommendation is to prevent an undesirable proliferation, in various countries, of subscriber control procedures for such services. Descriptions are given below of three control procedures schemes now in use or in various stages of evolution. Guidelines are offered to Administrations planning to offer subscriber controlled supplementary services. Reference is made to Annex A for a glossary of terms used in this Recommendation.

It is recognized that not all aspects of all supplementary services will affect the international telephone service, but a degree of international coordination is considered necessary because:

a) the same or similar supplementary services will exist on national and international networks; it is desirable to have similar control procedures for both applications;

b) a supplementary service which is only national now may be international in the future; in that case changes in control procedures might be impossible or expensive;

c) subscribers who travel or move will be less inconvenienced if control procedures for supplementary services do not change from one country to another;

d) compatibility between control procedures for telephone services and simple parallel end-to-end data transmission is highly desirable, because the same telephone instrument is used in both cases;

e) standardized control procedures make possible lower equipment and customer instruction costs.

Access to individual services requires that the supplementary service numbering plan have a sufficient capacity to meet all reasonable future needs; control of the services requires the ability to define functional requirements to the system.

The introduction of push-button telephones providing signals in addition to the normal decimal range (0-9) offers a means of providing the necessary function signals. Since the 12-button instrument is likely to be used by most subscribers, only two additional non-numerical signals will be available for control purposes. Study therefore has been directed towards evolving schemes for control procedures which are acceptable both from the human factors and technical aspects and do not require more than two non-numerical signals.

The same push-button telephone set that is used in dedicated telephone networks may be used as a subscriber instrument in service integrated networks. It is desirable that in this case the control procedures for a given supplementary telephone service still apply.

Where the normal 12-button telephone set is also used for services other than telephony, e.g. for data, videotelephone, etc., the control procedures used for these services should be compatible with the control procedures used for supplementary telephone services.