1、CEPT T/CS*2L-O2*E 84 2326434 0004574 2.- 21-02 Page E 1 Recommendation T/CS 21-02 (Montpellier 1984) CALL PROGRESS INFORMATION Recommendation proposed by Working Group T/WG 11 “Switching and Signalling” (CS) Text of the Recommendation adopted by the “Telecommunications” Commission: “The European Con
2、ference of Postal and Telecommunications Administrations, considering - that users making normal calls or using or encountering supplementary services require information relating to - that call progress information is subject to harmonisation; - that language difficulties should be avoided wherever
3、 possible; - that the operational requirements for related services such as call interception are defined in the “Handbook on services and facilities offered to the subscribers in modern telephone systems” prepared by Working Group SF i; call progress; O - that network utilisation should be minimise
4、d once an unsuccessful call has been detected, recommends that members of the CEPT adopt the following principles when providing call progress information.” 1. INTRODUCTION Call progress information (CPI) is provided to inform users of the current state of a call or request. This may enable them to
5、complete a call successfully or at least, inform them as precisely as possible of the reason for failure. By so doing, the action of network and its services are more intelligible to the user and ineffective traffic is minimised. Call progress information falls into two basic categories: call guidan
6、ce and call interception. In general terms, Cali guidance assists users to control supplementary services and complete calls successfully. Call interception is required to inform users of the reasons for call failure. 2. CALL GUIDANCE INFORMATION 2.1. Normal call tones The simplest form of call guid
7、ance, these tones such as dial tone and ringing tone tell the caller of the progress of the call towards completion. They are provided at their points of determination on the call path, usually origin and destination exchanges. Recommendations T/SF 14 2 and T/SF 17 3 give further details and Recomme
8、ndation T/CS 20-15 4 defines the exchange feature “Tones and announcements”. O 2.2. Supplementary service control Subscribers activating, interrogating and deactivating specific supplementary services do so with the assistance of prompts in the form of tones, or preferably, speciaiised recorded anno
9、uncements particular to each service. The announcements may be the same for all users of the service or may contain information specic to each call. See Recommendation T/CS 28-02 5. This type of guidance information is normally provided from the controlling exchange for the service. The wording of t
10、he announcement is not a subject for harmonisation but where recommendations for co-operative services have been produced the principle of the message to be conveyed is indicated where appropriate. For all services, the control procedures themselves are detailed in the SF Handbook. Examples of call
11、guidance for supplementary service control are: “Malicious call identification. has been activated.” “CCBS request accepted.” “Your CCBS call to 123 4567 is now being completed.” Alarm call booked for 7.15.” Edition of May 15, 1986 - CEPT T/CS*21-02*E 84 2326434 0004575 4 M TICS 21-02 E Page 2 Where
12、 specific announcements cannot be provided or are unnecessary, general acknowledgements or tones are acceptable if unambiguous to the user. 2.3. Cail encountering supplementary services A normal successful call may encounter a supplementary service which requires that the caller be informed. For exa
13、mple, on an incoming call to a line with immediate diversion activated, the caller may be informed: “This call is being diverted.” Such call guidance is valuable in preventing confusion when the call is answered by the third party. This type of information is normally provided from the controlling p
14、oint of the supplementary service. 3. CALL INTERCEPTION Calls which cannot reach the wanted number may be intercepted and diverted to an operator, an answering machine, or a tone to give the caller the appropriate information. 3.1. Diversion to an indication 3. I. 1. Drop back to local indication Ge
15、neral tones and announcements for common call failure situations in the enhanced network should be provided at the origin exchange (or as close to the origin as possible where interworking with unenhanced network parts is encountered). This is achieved by dropping back from the point of failure. The
16、re is considerable advantage in dropping back in this way as network switching and signalling utilisation is minimised and any announcements may be made in the originating subscribers language in the case of international calls. Drop back should not be applied to uncommon or complex call-specific si
17、tuations which should be dealt with as indicated in paragraph 3.1.2. or 3.1.3. below. A backward service instruction (SI) drop back to local call indication is required to perform the function together with a number of specific qualifiers. As the drop back SI is returned through the network each exc
18、hange initiates the clearing of any speech path associated with the original call. For this reason drop back is only utilised where a speech path is no longer required. Each drop back situation may not be translated on a one to one basis to specific tones or announcements. A number of similar failur
19、e situations may be indicated to the caller by means of a single announcement, but for network management purposes, more detailed information is available. Indication from the point of failure In the unenhanced network or where more specific information about the reason for failure can be conveyed,
20、the call may be diverted to a tone or announcement local to the point of failure. An example of such specific information is the notification of changes to published information relating to telephone numbers or codes which are frequently called. Diversion to remotely provided indication In the situa
21、tions of paragraph 3.1.1. or 3.1.2. above, where diversion to an indication would be appropriate but for economic reasons it cannot be provided at the network points indicated, the call may be diverted to a remote exchange where the indication is available in a so called “remote call progress inform
22、ation facility”. This facility may be reached either by means of ageneral network address whereby the specific indication required is conveyed by means of a service instruction, or each specific indication may be reached by means of a separate network address. In the latter case, the call to the rem
23、ote CPI facility may be class-marked in order to prevent the latter from being reached by normal calls. Operators can provide the most effective method of disseminating detailed information, for example changes to individual numbers where traffic levels are low, but they are expensive. Where justifi
24、ed, this type of interception may be provided by means of the call diversion service utilising the principles of immediate diversion where the point of failure is the B-exchange and the remote operator the C-subscriber. The diverted call SI may be used to provide an indication to the operator that t
25、he call has been intercepted. 3.1.2. 3.1.3. 3.2. Diversion to an operator 4. LIST AND DEFINITIONS OF SERVICE INSTRUCTIONS The service instructions according to Recommendation T/CS 20-26 6 required for provision of call progress information are: - Edition of May 1 986 CEPT T/CS*23-02*E 84 2326434 O00
26、4576 b TICS 21 -02 E Page 3 4.1. Drop back to local indication A backward (circuit related) SI which causes an appropriate indication (determined from an associated qualifier) to be applied to the call at the nearest possible point to its origin. The speech path is cleared link by link as the SI pas
27、ses back. The following drop back SI quasers have been identified: Connection temporarily unavailable. Unaliocated number. Connection not admitted. Congestion tone. General call failure. Subscriber busy. Special information tone. Supplementary service incompatibility. This list is not exhaustive and
28、 further qualifiers may be added to cover other common call failure situations subject to their justification on grounds of economy. 4.2. Ca to remote call progress information facility An optional forward (circuit related) SI sent together with the call Set-up information indicating that the call i
29、s destined for a remote CPI facility. The qualifiers defned for drop back to local indication SI apply. References i CEPT Handbook on services and facilities offered to subscribers in modern telephone systems. Sections L and II: Services and facilities within the public network. Prepared by CEPT Wor
30、king Group SF, 3rd edition 1981. 2 CEPT Recommendation T/SF 14. Applications of tones and recorded announcements in telephone services. 3 CEPT Recommendation T/SF 17. Timing and sequence of tones and recorded announcements. 4 CEPT Recommendation T/CS 20-15. Tones and announcements. 5 CEPT Recommendation TICS 28-02. Names and meanings of tones and general designations for verbal announce- ments. 6 CEPT Recommendation T/CS 20-26. Additional signalling. . Edition of May 15, 1986 - /
