Recommendation U.40
REACTIONS BY AUTOMATIC TERMINALS CONNECTED TO THE TELEX NETWORK
IN THE EVENT OF INEFFECTIVE CALL ATTEMPTS
OR SIGNALLING INCIDENTS
(Geneva, 1980; amended at Malaga–Torremolinos, 1984;
and at Melbourne, 1988)
	The CCITT,
considering
	(a)	that equipment capable of automatically originating calls in the telex network can repeat unsuccessful calls until the call has been set up;
	(b)	that unlimited repetition of call attempts may cause congestion in the telex network;
	(c)	that manufacturers of automatic terminals for connection to the telex network should be given guidance on tolerable numbers of repeated call attempts and simultaneous calls;
unanimously declares the following view:
1	Ineffective outgoing call
1.1	Non–return of the call–confirmation and/or proceed–to–select signal(s)
1.1.1	The call signal could be maintained for a maximum period of 20 s. If, within this period, the call–confirmation and/or the proceed–to–select signal(s) have not been received from the network, the terminal sends the clear signal.
1.1.2	A further call attempt must not be made within a minimum period of 20 s.
1.1.3	After three such ineffective attempts, the incident should be reported to the staff at the terminal installation, specifying the nature of the fault.
1.2	Slow or incomplete selection
1.2.1	Once the terminal has sent a call signal and has received the call–confirmation and/or proceed–to–select signal(s), transmission of the selection digits must commence within a period of between 0.5 and 7 s, depending on the national network. If this delay is exceeded, the network may clear.
1.2.2	The same procedure applies in the event of incomplete selection by the terminal or, if an interval longer than 7 s occurs, between two selection digits.
1.3	No response after selection
1.3.1	If, after selection has been completed (but before the call has been set up), the terminal receives no signals within 60 s, it may send the clear signal. This delay may be increased to 120 s for international calls.
1.3.2	Further attempts may be made in accordance with §§ 1.1.2 and 1.1.3 above.
1.4	Ineffective attempts followed by service signals
1.4.1	OCC
1.4.1.1	If, after initiating a call, the terminal receives an OCC service signal followed by clear, it must wait at least 60 s before repeating the attempt. If OCC is received again, then second, third and fourth attempts shall be permitted at 180–second intervals.
1.4.1.2	If the distant terminal is still unavailable after a maximum of four such reattempts, this should be reported to the staff at the terminal installation indicating the number called and the service code received. Ten series of a maximum of four reattempts per series may be carried out at intervals between 480 and 3600 s, between each series.
1.4.1.3	Should the distant terminal remain unavailable after these call series, this should be reported and the call abandoned as far as the automatic terminal is concerned.
1.4.2	NC
1.4.2.1	If, after initiating a call, the terminal receives an NC service signal followed by clear, it must wait at least 60 s before repeating the attempt.
1.4.2.2	If the distant terminal is still unavailable after a maximum of four such reattempts, this should be reported to the staff at the terminal installation indicating the number called and the service code received. Ten series of a maximum of four reattempts per series may be carried out at intervals between 480 and 3600 s, between each series.
1.4.2.3	Should this second series still fail to reach the distant terminal, this should be reported and the call abandoned as far as the automatic terminal is concerned.
1.4.3	NA, NP, NCH or the service code CI
1.4.3.1	If, after initiating a call, the terminal receives an NA, NCH or NP service signal followed by clear, only one reattempt may be made after a minimum period of 2 s.
1.4.3.2	In the event of a second failure due to a service signal specified in § 1.4.3.1, the terminal should abandon the call and report the incident to the staff at the terminal installation indicating the number called and the service code received.
1.4.3.3	If the terminal receives the service code CI followed by clear, the procedure described in §§ 1.4.3.1 and 1.4.3.2 should also be applied.
1.4.4	DER, ABS
1.4.4.1	If after initiating a call, the terminal receives a DER or ABS service signal followed by a clear, it must wait 30 minutes before repeating the attempt.
1.4.4.2	If the first repeated attempt is unsuccessful, another attempt may be made 30 minutes later. The terminal must then wait two hours before repeating the series of two attempts spaced 30 minutes apart.
1.4.4.3	If the distant terminal is still unavailable after these attempts, further series of attempts can be made after a delay of 15 minutes to 2 hours. A total of 5 such series may be made with two attempts per series.
1.5	Ineffective calls characterized by a clearing signal without a preceding service signal
1.5.1	If after having made a call, the terminal equipment receives a clearing signal without previous reception of a service signal, it must wait 2 s before a second attempt.
1.5.2	If the same phenomenon occurs three times in succession, a second series of three calls may be made again after a delay of 15 minutes.
1.5.3	If the second series of calls produces the same result, the terminal equipment should definitively abandon the call and report the incident to the staff at the terminal installation indicating the number called and that no service code was received.
1.6	Reception of an answerback
1.6.1	If, after having made a call, the terminal equipment receives an incorrect answerback, it may send the clearing signal and repeat the call only once after a period of 2 s.
1.6.2	If the second attempt fails in the same way, the terminal should abandon the call and report the incident to the staff at the terminal installation, indicating the number called and the fact that the expected answerback code was not received.
1.7	Simultaneous calls
1.7.1	If an automatic terminal equipment can initiate simultaneous call attempts on a number of outgoing lines, the number of such call attempts in progress at any one time shall not exceed a maximum prescribed by the Administration concerned.
1.7.2	In no case shall a multiple–line terminal equipment be allowed to present the same call simultaneously on more than one telex line. Moreover, the periodicity of a given repeated call and the number of attempts to be made in case of failure shall apply to this terminal equipment as indicated in Table 1/U.40, irrespective of whether the call is presented on the same line or on different lines.
2	Ineffective incoming calls
2.1	False calls
2.1.1	The terminal should disregard any “call” signal from the network that does not exceed 50 ms in duration.
2.1.2	If the terminal receives no signals within a period of up to 30 s after it has recognized a call signal from the network, it should return the clear signal to the network.
3	Incidents following call set–up
3.1	Idle circuit without clearing signal
3.1.1	Barring prior agreement to the contrary, if no signal is received after the beginning of the call or if the distant correspondent's transmission stops during an incoming call (i.e. steady stop polarity on the incoming path) for a period of more than 2 minutes, the receiving terminal may clear the call and report the incident to the staff at the terminal installation, indicating the nature of the suspected fault and, if possible, the number of the distant subscriber.
3.2	No clear–confirmation
3.2.1	Should the network fail to return the clear–confirmation signal after the terminal has been sending a clear signal for 10 s or more, the terminal should report the incident (giving the time at which it occurred) and withdraw the circuit from service until the necessary action has been taken.
TABLE 1/U.40

Montage:  Reprendre les originaux du Livre Rouge (sans corr.)