Recommendation U.70
TELEX SERVICE SIGNALS FOR
TELEX TO TELETEX INTERWORKING
(Malaga–Torremolinos, 1984)
	The CCITT,
considering
	(a)	that a basic interworking on international connections will be at 50 bauds using an international telex network and that any telex subscriber can call conversion facilities in various countries;
	(b)	that Recommendation F.201 specifies:
–	that a validation of a called Teletex terminal is mandatory. The validation is performed either by a direct validation call or by a data base access;
–	that if a message delivery to a Teletex terminal fails in the case of interworking with two–stage selection procedure, the conversion facility should send a non–delivery notification to a telex terminal;
	(c)	that Recommendation S.90 specifies Teletex requirements for interworking with the telex service and Recommendations S.62 and S.70 specify control procedures and a network–independent basic transport service for a Teletex;
	(d)	that Recommendation X.96 specifies call progress signals in a public data network,
unanimously declares the following view
1	Scope
	This Recommendation defines service signals which are to be sent back to the telex terminal in the event of unsuccessful validation for called Teletex terminal addresses, and service signals of the last delivery attempt to the Teletex terminal which are to be sent to the telex terminal as a part of non–delivery notification.
TABLE 1/U.70

MONTAGE: REPRENDRE ORIGINAUX DU LIVRE ROUGE.
PAS DE NOUVELLE SAISIE = MAINTENU LIVRE ROUGE
2	Principles
	The following principles should be taken into consideration:
2.1	Call progress signals arriving from the Teletex network will be converted without changing their original meaning as far as possible.
2.2	A faulty condition between the Teletex network and the conversion facility will be regarded as a faulty condition within the network.
2.3	A faulty condition between the Teletex network and the Teletex terminal will be regarded as a fault of the terminal.
3	Telex service signals
	1n general, telex service signals specified in Recommendation F.60 should be used. However, the telex service signals listed below will be used in the following circumstances:
3.1	1f the format of the Teletex address part is incorrect, the service signal NP will be returned.
3.2	1f the direct validation call is unsuccessful, the conversion facility will transmit the service signals specified in Table 1/U.70 to the telex terminal.
3.3	If the validation by data base access is unsuccessful, the conversion facility will transmit the service signals specified in Table 2/U.70.
3.4	If the message delivery to the Teletex terminal is unsuccessful, the conversion facility will transmit the service signals of the last delivery attempt which are specified in Table 1/U.70, as a part of non–delivery notification to the telex terminal.
TABLE 2/U.70
Service signals for unsuccessful validation by data base access
 Abnormal conditions	 Service signal	
 Unsuccessful results	 NP	
Note – In addition to the case “the number does not exist”, other cases, for example, “the number is being temporarily prohibited” or “the number is out of order”, might be considered as abnormal conditions. But at this moment such conditions and the service signals corresponding to them are for further study.