1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 1 TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU).4%27/2+).G0G0/b) newly developed systems should not lead to any modification to the specifications covering the presentsignalling systems except that the translation of new interworking events arising from
2、the meanings of newsignals in the new system will need to be defined for the existing signalling systems.In order that the new signals should cause the minimum loss or gain of information when interworking withexisting signalling systems, any new signals should, if possible, not contain any informat
3、ion elements already existing.Hence it is better that these new signals convey only a single meaning rather than a multiple meaning as occurs in someexisting systems (e.g. Signalling System R2 signal I-14 corresponds to FITE 8 which combines the elements of FITE 3and FITE 5). Therefore, only one new
4、 information element will be associated with the new signal and only one newFITE or BITE will be needed.In some cases the new signal will be translated into a presently defined signal of an existing system and hencewill cause the addition or, more often, the loss of information. In some cases, no el
5、ectrical signal being available, all theinformation may be lost or a tone may need to be used. In the case of Signalling Systems R2, No. 6 and No. 7, somereserved signals exist within the capacity of these systems and such signals may be introduced to enhance the signallingsystem and provide an inte
6、rworking capability.However it should be borne in mind that with such existing systems, it may not be easy or desirable to modifyexisting equipment, and even if such modification were possible, in the transitional period the interworking of existingand enhanced signalling equipment of the same syste
7、m must also be considered.In view of the difficulties of interworking with existing signalling systems, new features of signals should onlybe introduced in a new system if there are good operational reasons for doing so.7.2 Reserve for national useIn practice, provision of appropriate spare signalli
8、ng capacity in a new system reserved for national/regional usecannot be avoided. In such a case, precautions must be taken to prevent signals with an individual national meaning fromentering the international network.One general objective of a new signalling system should be to meet also the nationa
9、l requirements in order toavoid national versions of a given signalling system as far as possible.2 Fascicle VI.6 - Rec. Q.6077.3 Unambiguous specificationsAfter a clear specification of a new feature to be included in a signalling system, the related signallingprocedures should be specified in a un
10、ique and standard form. The same applies to the signals involved.The designation of signals of different signalling systems, which carry the same information, should be thesame.7.4 Escape codesIt is obvious that appropriate spare capacity should be provided in order to cope with future demands. One wayof doing so is the provision of escape codes.
