Recommendation U.41
CHANGED ADDRESS INTERCEPTION AND CALL REDIRECTION
IN THE TELEX SERVICE
(Geneva, 1980; amended at Melbourne, 1988)
Definitions
	For the purpose of this Recommendation the following definitions shall apply:
–	Subscriber A is the calling subscriber;
–	Subscriber B is the redirecting subscriber;
–	Subscriber C is the subscriber to which the call shall be redirected.
	The CCITT,
considering
	(a)	that, with fully automatic working between telex subscribers, it is desirable to envisage the possibility of:
–	a fully automatic changed address interception facility,
–	a fully automatic call redirection facility;
	(b)	that the operation of such facilities has an influence upon telex calls originated by other Administrations and therefore requires international standardization;
	(c)	that operation in networks employing signalling systems according to Recommendations U.1, U.11 and U.12 must be considered;
	(d)	that the described facilities in the called network must be compatible with existing call setup procedures in the originating and transit network(s),
unanimously declares the following view
1	Changed address interception
1.1	In existing networks, in the case of a call to a subscriber whose number has been changed, the incoming network may return the service code NCH. The service signal is not preceded by the call connected signal. It is always followed by the clearing signal in accordance with Recommendation F.60 [1], U.1 (§ 10.1 and Table 1b/U.1) and U.11 (Table 1/U.11).
1.2	In new networks and as far as possible in existing networks, it would be desirable to inform the calling subscriber of the new number to be selected by means of a suitable sequence of signals, which should have the following format:
			<- = NCH:x. . .x <- =  (where x. . .x represents the figures of the new number),
followed by the clearing signal. This sequence must be preceded by the call–connected signal. A pause of at least two seconds must be provided between the beginning of the call connected signal and the beginning of the NCH service sequence defined above. Every step should be taken to ensure that the period between the call–connected signal and the clearing signal does not exceed 5 seconds, in order to avoid accounting in accordance with Recommendations U.1 and F.61 [2].
1.3	Operating Administrations may optionally offer automatic redirection to the new number of a call to one of their subscribers whose number has been changed. This redirection will be in accordance with § 2 below, and the sequence “RDI” as specified under § 2.1 below shall then apply. Under no circumstances shall the NCH sequence be preceded by the RDI service sequence. This supplementary service shall be available for a limited period only. It may not be offered beyond the time during which the Administration informs calling subscribers of the change in the call number.
2	Call redirection
2.1	In new networks and as far as possible in existing networks, a call redirection should be signalled by the return to the calling station of a sequence of signals constituted by the code expression RDI followed by the indication of the new number to which the call is redirected, in accordance with the following format:
			<- = RDI:x. . .x <- =  (where x. . .x represents the new number),
followed if necessary by further letter–shifts (); the total number of characters in the sequence may in no case exceed 20.
	Failing this, at least the code expression RDI, as specified in Recommendations U.1 and F.60, without any further indication, should be returned.
2.2	The call redirection sequences specified in § 2.1 above must always follow the call connected signal. A period of two seconds must elapse between the beginning of the call connected signal and the beginning of the RDI sequence. The answerback of the Subscriber C will then be returned to the Subscriber A in accordance with the procedures outlined in Recommendation U.1, § 7. (It should be noted that there are networks which return the RDI–sequence after the answerback sequence and in addition to the NCH and new call number.)
2.3	Administrations offering call redirection facilities should take all necessary technical and administrative steps to ensure that the same call can in no circumstances give rise to more than one redirection and that the total number of circuits used to establish the call after redirection does not exceed the maximum tolerated in the transmission plan for the national network.
2.4	With regard to the call redirection facility, redirection should not take place to addresses outside the jurisdiction of the Administration performing the redirection function, therefore the new address shall consist only of the national number.
2.5	Interworking between automatic terminals, Teletex to telex conversion facility and other services in the originating network and a redirected subscriber station in a terminating network is for further study.
References
[1]	CCITT Recommendation Operational provisions for the international telex service, Rec. F.60.
[2]	CCITT Recommendation The chargeable duration of a telex call, Rec. F.61.