Recommendation E.424
TEST CALLS
1	General
	Test calls carried out manually or automatically to assess the functioning of international circuits of connections are of four types:
a)	Type 1 test call
	A test call conducted between two directly connected international centres to verify that the transmission and signalling on an international circuit of a given group are satisfactory.
b)	Type 2 test call
	A test call conducted between two international centres not directly connected to verify transit operational facilities of an intermediate international centre.
c)	Type 3 test call
	A test call from an international centre to a subscriber type number in the national network of the distant country, generally as a result of a particular kind of fault.
d)	Subscriber–to–subscriber type test call1) 
	A subscriber–to–subscriber type test call is a test call from a test equipment having the characteristics of an average subscriber line in one national network to a similar equipment in the national network of a distant country.
	Test calls types 1, 2, 3 and subscriber–to–subscriber test calls must not interfere with customer traffic. If, however, test calls contributing a significant load on a part of a network are to be made, prior advice should be given to the other Administration(s) concerned. Types 1 and 2 test calls for preventive maintenance should be conducted during light load periods. Types 1 and 2 test calls should be conducted as and when required for the investigation and clearance of faults.
	Type 3 test calls should be conducted only after adequate testing has been done by means of type 1 or 2 test calls and after the distant Administration has made the necessary check in its national network. Type 3 test calls should be conducted during light load periods.
	In order to find faults in last–choice equipment, circuit multiplication equipment or in–circuit multiplexing equipment, it may be necessary for tests to be carried out at the time when the traffic load approaches the full capacity of the route under test. The agreement of the distant network analysis point will be necessary before this test is carried out.
	Subscriber–to–subscriber type test calls can be made by agreement of the network analysis point in the countries concerned.
	Normally, unless there is a specific agreement between the Administrations concerned, subscriber–to–subscriber type test calls would be considered for fault location after:
1)	verifying that there are no evident faults in the international switching centres involved that would cause the poor quality of service or subscriber complaint being investigated;
2)	verifying that type 1 or type 2 test calls have been made on the international circuits that might have been involved;
3)	verifying that there are no evident faults in the national network from the outgoing exchange to the international centre in the originating country;
4)	verifying that there are no evident faults in the national network in the distant country, from the international centre to the called exchange.
	When test calls are undertaken from the international centre to a subscriber number to verify that there are no evident faults in the national network, such calls should be routed through the international centre on the same path as a normal incoming international call. Using the test access facilities in the international centre could route calls via a different path thereby masking a fault.
	When subscriber–to–subscriber type test calls are made, the network analysis point in the two countries should consider such factors as:
i)	the expected nature of the fault;
ii)	international accounting agreements;
iii)	the need for making the test calls in the busy hour;
iv)	the possibility of causing or aggravating congestion at the time the calls are made.
	The responding equipments used for subscriber–to–subscriber type test calls could be those used for maintenance of the national network.
2	Results of test calls (see Table 1/E.424)
TABLE 1/E.424
Results of test calls
International outgoing exchange:		Type of test call	

Circuit group:		Type 1 a)
Type 2 a)
Type 3 a)	
Service	semi–automatic a)
	automatic a)	Sub–to–Sub a)	
Period from		to		
	Number	Percentage	
Category	Subtotal	Total	Subtotal	Total	
1.	Satisfactory tests 			. . .		. . .	
2.	Signalling and charging faults 			. . .		. . .	
	2.1	Wrong number 		. . .		. . .		
	2.2	No tone, no answer 		. . .		. . .		
	2.3	Absence of a backward line signal 		. . .		. . .		
	2.4	Other faults 		. . .		. . .		
3.	Transmission faults 			. . .		. . .	
	3.1	Conversation impossible 		. . .		. . .		
	3.2	Call overamplified or underamplified 		. . .		. . .		
	3.3	Noise 		. . .		. . .		
	3.4	Fading 		. . .		. . .		
	3.5	Crosstalk 		. . .		. . .		
4.	Congestion 			. . .		. . .	
 5.	Other faults 		. . .	 . . .	 . . .	 . . .	
	. . .		. . .		
Tests carried out 			. . .		100	
Tests procedure followed (apparatus used, destination of calls, etc.)

a)	Detele whichever is inapplicable.