1、CEPT T/CS*20-22*E 83 = 2326434 0004554 7 m- TtCS20-22E Page 1 Recommendation TICS 20-22 (Cannes 1983) FEATURE DIRECT DIALLING-IN (DDI) Recommendation proposed by Working Group T/WG 11 “Switching and Signalling” (CS) Text of the Recommendation adopted by the “Telecommunications” Commission: “The Euro
2、pean Conference of Postal and Telecommunication Administrations, considering - that SPC-exchanges allow a flexible numbering allocation; - that SPC-exchanges allow a flexible subscriber line signalling handling; - that in several CEPT member countries, the service direct dialling-in is offered which
3、 may involve the feature direct dialling-in, recommends to the members of the CEPT, usage of the following definitions, arrangements and specifications for the feature direct dialling-in.” e 1. DEFINITION The ability of an exchange to transfer address and other appropriate call handling information
4、to a PABX for the purpose of setting up a call to its extensions without assistance of the PABX operator. 2. DESCRIPTION The DDI feature enables subscribers to dial, from the public switched network, directly to an extension. Extension numbers of DDI PABXs are part of the national numbering plan. Th
5、e feature is required for terminating calls to a DDI PABX. 3. TECHNICAL CHARACTERISTICS On detection of a DDI call set-up requirement, the exchange will operate in a transit mode Le. gathering of address information from the network and forwarding the necessary address information to the DDI PABX. F
6、urthermore some call handling functions (e.g. sending of ringing signal to the B-subscriber, recognition of E-answer, sending of backward signals to the public network, etc.) may no longer be performed by the exchange but be delegated to the PABX. A specific DDI signalling serves this purpose. The D
7、DI feature of an exchange should not affect the possibilities of setting up - incoming NON-DDI calls and/or - outgoing calls. Besides normal PABX line signals the typical DDI messages to be interchanged are: Address information whose transfer may be initiated by a proceed-to-send, indication and may
8、 be acknowledged by an address received - and/or an end-ofselection indication. In some cases a condition B-extension information is needed to indicate the state of the line of the called extension. The signalling system is not part of this Recommendation. 4. UTILISATION The feature is required for
9、DDI-service. 5. REFERENCES SF Handbook. Note: The studies on this series (T/CS 20) of Recommendations for the features in an analogue environment has now been terminated. A continuation of the studies has started with the aim to amend these existing features, where necessary, and to specify new features for the ISDN. These Recommendations will be gathered in a new series of Recommendations. O E t Edition of May 15, 1986
