Recommendation U.4
EXCHANGE OF INFORMATION REGARDING SIGNALS 
DESTINED TO BE USED OVER INTERNATIONAL CIRCUITS 
CONCERNED WITH SWITCHED TELEPRINTER NETWORKS
(former CCIT Recommendation E.4, Geneva, 1956;
modified at New Delhi, 1960 and Geneva, 1972)
	The CCITT,
considering
	(a)	that certain signals and certain characteristics of signals used in the international telex service have been standardized in Recommendation U.1;
	(b)	that certain Administrations have introduced automatic telex transit switching facilities based upon the signalling standards shown in Recommendation U.1;
	(c)	that standardized signals for the European switched network for the public telegram service (gentex network) are advocated in Recommendation U.30;
	(d)	that in view of the foregoing an exchange of information regarding the precise nature of the signals proposed to be used in the above–mentioned services by interested Administrations would be very useful;
	(e)	that certain Administrations have already supplied such details regarding their telex services in a useful form (see supplements to the documents of the VIIIth Plenary Assembly of the CCIT, and subsequent Plenary Assemblies of the CCITT),
unanimously recommends
	that Administrations concerned in the international telex service and gentex network be invited to supply to the CCITT time–sequence diagrams showing in each case the signals at present transmitted or proposed to be transmitted over the international circuit for incoming calls. The diagrams should show not only the sequence and characteristics of the signals, but also the timing tolerances to be expected. The diagrams should show the signalling conditions applicable to transit as well as to terminal calls, including any conversion of the signals that are received from the destination network.