1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 ) TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU).4%2!4%$G0G03%26)#%3G0G0$)4!,G0G0.%47/2+G0 )3$.G93%26)#%G0G0#!0!“),)4)%3$%A an additional teleservice which may be available in some ISDNs, and which may also be availableinternationally;FS the recommended s
2、upport of this teleservice is for further study,b) with each teleservice, a description of the agreed non-dominant attributes, e.g. values of the high layerattributes: layer 4 to 7 protocol functions. If an ISDN supports the teleservice, the recommended supportof the values of these secondary attrib
3、ute combinations within this teleservice is described as:E an essential combination of attribute values to be made available internationally (when an ISDNsupports the particular teleservice);A an additional combination of attribute values which may be available in some ISDNs, and which mayalso be av
4、ailable internationally (when an ISDN supports the particular teleservice);FS the recommended support of this combination of attributes is for further study.Note - During an evolutionary period, not all items marked “E” will be provided in all networks.The recommended overall support of teleservices
5、 as given in Recommendation I.241 is summarized inTable 1/I.240.4 Prose definitions of teleservicesIn order to give an overview of the teleservices identified, their definitions, as given in Recommendation I.241,are reproduced below.I.241.1 TelephonyThe “telephony service” provides users with the ab
6、ility for real-time two-way speech conversation via thenetwork.I.241.2 TeletexTeletex is an international service enabling subscribers to exchange office correspondence in the form ofdocuments containing Teletex coded information on an automatic memory-to-memory basis via the ISDN.I.241.3 Telefax 4T
7、elefax 4 is an international service enabling subscribers to exchange office correspondence in the form ofdocuments containing facsimile coded information automatically via the ISDN.Fascicle III.7 - Rec. I.240 3TABLE 1/I.240Recommended overall support of teleservices by ISDNsNo. Service SupportI.241
8、1 Telephony E/Aa)I.241.2 Teletex AI.241.3 Telefax 4 AI.241.4 Mixed mode AI.241.5 Videotex AI.241.6 Telex FSa)It is anticipated that ISDNs will offer telephony as a basic telecommunicationservice. Some networks will offer this as a teleservice. However, due tonational regulation policies, some netwo
9、rks will offer telephony as a bearerservice rather than as a teleservice.I.241.4 Mixed modeThis service provides combined text and facsimile communication (mixed mode) for end-to-end transfer ofdocuments containing mixed information of text and fixed images. The high layer attributes are based on th
10、eRecommendations for Teletex and Telefax 4.I.241.5 VideotexThe Videotex service in the ISDN is an enhancement of the existing Videotex service with retrieval andmailbox functions for text (alpha) and graphic information.I.241.6 TelexThis service provides interactive text communication. The digital signal at the S/T reference point follows theinternationally agreed Recommendations for telex above the ISDN physical layer.
