Recommendation U.31
PREVENTION OF CONNECTION TO FAULTY STATIONS
AND/OR STATION LINES IN THE GENTEX SERVICE
(former CCIT Recommendation E.9, Geneva, 1956)
	The CCITT,
considering
	(a)	that correct reception of the answerback code at the beginning and end of a telegram should safeguard the correct transmission of the telegram;
	(b)	that it accordingly becomes essential to provide adequate signalling for cases when a teleprinter is temporarily unable to participate in the international service, on account of paper trouble, faults, etc.;
unanimously declares the view
	(1)	that faults during the transmission of a telegram shall be signalled as far as possible by the automatic transmission of a clearing signal;
recognizing, however,
	that it will be impossible to signal all faults that may occur on an established connection,
unanimously declares the view
	(2)	that it is essential that absence of paper on a receiving teleprinter should be signalled by the clearing signal; and
	(3)	that, since the receiving Administration is responsible for the receipt of the telegram when the answerback signals have been correctly exchanged, it is responsible for making the necessary arrangements to ensure security of operation (for example, if the tape should break or become jammed);
	(4)	that in the case of a faulty station line or teleprinter at the moment of the call, the existing automatic switching networks use one or more of the following signalling conditions : no call–connected signal, busy signal, service code DER or no return of answerback. All these signalling conditions ensure that a telegram is not transmitted over a faulty connection;
	(5)	that in the case of a faulty station line out of an office group it is essential that the faulty line should be busied out as quickly as possible so that traffic may be offered automatically to all the other lines in the group.