1、CEPT T/CS*20-25*E 82 = 2326434 0004558 4 W G9 20-25 Page 1 E Recommendation T/CS 20-25 (Vienna 1982) CALL DIVERSION Recommendation proposed by Working Group T/WG .11 “Switching and Signalling” (CS) Text of the Recommendation adopted by the “Telecommimications” Commission: “The European Conference of
2、 Postal and Telecommunications Administrations, considering - that in accordance with the principles outlined in Recommendation TICS 20-01 i, the exchange and network features which are required for the implementation of services and facilities should be identified and specified; - that in several C
3、EPT member countries, supplementary services will be offered which imply the diversion of a call to another telephone number, to an operator or to a device producing an audible indication; - that it is desirable to handle such calls in a standardised way especially when these calls are crossing bord
4、ers, o secommends that the members recognise and use the following definitions, arrangements and specifications for the feature call divession.” 1. DEFINITION The call diversion feature is the ability of the network to route a call, during the set-up phase, to a destination other than that indicated
5、 by the address information received from the origin of the call. 2. DESCRIPTION 2.1. The following terminology applies : A = the origin of the call; B = the destination of the call as indicated by the address information sent by A; C = the destination to which the call has to be diverted according
6、to the conditions applying at B; D = the destination to which the call has to be diverted according to the conditions applying at C. The A-exchange is the exchange to which A is connected; the same applies when A is substituted by B, C or D. The I-exchange is an intermediate exchange on the call pat
7、h from the A-exchange to the B-exchange, from where a new call path to C may be Set-up. 2.2. Depending on the conditions applying at B, the call may be routed to: (a) another subscriber termination; (b) a public network operator; (c) tone or announcing equipment; other than that indicated in the ori
8、ginal address information. This implies that: - a new call path has to be Set-up from the A-, I- or B-exchange to C; - the established OS seized call path has to be cleared at the point from which the new call path is to be The diversion of the call may take place: (a) immediately, i.e. as soon as t
9、he call arrives at B; (b) on no reply, i.e. after a certain time during which the ringing condition has been applied to B; (c) on busy, i.e. only if B is busy. Set-up (this will not apply if the new call path is Set-up from the B-exchange). 2.3. Note: The studies on this series (T/CS 20) of Recommen
10、dations 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.
11、- Edition of May 15, 1986 .CEPT T/CS*20-25*E 82 2326YLLi OOOLi559 b H TICS 20-25 Page 2 2.4. 3. 3.1. 3.2. 3.3, 3.4. 3.4.1. From the routing point of view the following types of call diversion are identified: (a) internal diversion, when C is connected to the same exchange as B or to a remote control
12、led switching unit, which is controlled by the -exchange; (b) call forwarding, if the new call path is Set-up from the -exchange to another exchange; (c) rerouting, if the new call path is set-up froin the A- or an I-exchange; (d) drop back, in the case of diversion to tone or announcing equipment,
13、connected to the A- or an I-exchange. Note: The transfer of an established (answered) call (as required by the fi111 three-parry service) is not covered by the feature call diversion. TECHNICAL CHARACTERISTICS When applying call diversion, the following aspects require special attention : - addition
14、al signalling for call Set-up; - transmission quality; - prevention of multiple diversion of calls; - charging aspects; - post-dialling delay; - exceptional treatment of calls involved in call diversion. These aspects will be treated in the following paragraphs, with respect to the different types o
15、f call diversion from the routing point of view where applicable. Additional signalling for call set-up The additional signalling feature as described in Recommendation T/CS 20-26 2 will be required in combination with the call diversion feature as follows: - with call forwarding, additional signall
16、ing on the link from the B-exchange to the C-exchange is required in order to indicate the diverted nature of the call (the C-exchange may need this information, see 9 3.5.1. below). Additional signalling on the link from the A-exchange to the B-exchange may be required to inform subscriber A that h
17、is call is being diverted; - with rerouting, additional signalling is required between the A- and the B-exchange and between the A- and the C-exchange; - for drop back, additional signalling is required in order to be able to send an announcement with supplementary information from an exchange which
18、 is situated as close as possible to A; - for internal diversion, no additional signalling is required. In 3 the utilisation of the additional signalling information for call diversion is shown in detail. Transmission quality Transmission quality is only endangered during call forwarding. In this ca
19、se, the diverted call may not meet the requirements for normally routed calls, two such calls being connected in tandem. Factors which require attention are: - excess of the attenuation allowed; - excess of the maximum number of two-wire/four-wire conversion; - excess of the transmission delay time
20、allowed due to the number of digital exchanges; - excess of the maximum number of analogue/digital conversions. Multiple diversion of calls Multiple diversion is understood to be the diversion of an already diverted call, e.g. from C to D according to the terminology defined in Section 2.1. Where re
21、quired by Administrations, provision must be made to prevent multiple diversion of calls. Charging Aspects For call diversion, the following possible ways of charging have been identified. (a) Subscriber A is charged for a normal call from A to B, subscriber B is charged for a normal call from B to
22、C. In the case of call forwarding, no additional signalling is required for this type of charging. In the case of rerouting, additional signalling is required between the A- and B-exchanges to provide the B-exchange with information for charging the B-subscriber. It may be required to charge subscri
23、ber for a call at a special rate, in the case that the sum of the charges of the calls from A to B and from B to C would be lower than the charge of a normal direct call from A to C. This will, however, not affect the required additional signalling. 3.4.2. 3.5. 3.5.1. 3.5.2. 4. CEPT T/CS*20-25*E 82
24、2326434 0004560 2 = TICS 20-25 E Page 3 (b) Subscriber A is charged for a normal call from A to C, subscriber B is not charged. In this case, no additional signalling is required for charging. Before the diverted call is established, an announcement should be given to the caller if the charges for t
25、he call from A to C are higher than the expected charges for a call from A to B. (c) Subscriber A is charged for the rate of the normal call from A to B or from A to C, whichever is lower. Subscriber B is charged for the rate difference between normal calls from A to B and from B to C; if this diffe
26、rence is negative, subscriber B is not charged. Additional signalling is required to transmit the charge difference to the B-exchange. At present, no common preference exists for a certain type of charging. The type of charging mentioned in Paragraph 3.4.1s. is at present not suited for calls where
27、subscribers A and B are connected to different national networks. Exceptional treatment of calls involved in call diversion An option should exist for the C-subscriber to prevent calls from being diverted to his termination. If this prevention is activated, such calls should be diverted to an approp
28、riate announcement. When a supplementary service has been activated which impiies diversion to another telephone number, it should be possible for calls of a special nature arriving at B, not to be diverted but to arrive at termination B. Note: Such a special call is, e.g. a call that matures due to
29、 the operation of the supplementary service completion of calls to a busy mbsaiber, activated at B. UTLISATION The feature is required for the supplementary services according to the CHEST Action list as shown on Table 1 (T/CS 20-25). Supplementary service Call progress information Absent subscriber
30、/do not disturb service Diversion of calls to an- other number Call interception Feature required for diversion to Tone or announcing equipment Tone or announcing equipment, operator Another number (a) immediate (b) on no reply (c) on busy Tone or announcing equipment, operator Table 1 (T/CS 20-25). References 11 Recommendation T/CS 20-01. Exchange and network features. 2 Recommendation T/CS 20-26. Additional Signalling. 3 Recommendation TICS 21-08. Call handling sequences for dverson of telephone calls to another telephone number. Edition of May 15, 1986
