936 THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1956 



Repeat-2 Tests. This consists essentially of two code 103 tests on the 

 same trunk in rapid succession. It is used to insure that a connection 

 through the switching train in the distant office will be properly broken 

 down when a call is completed. 



Repeat Test. A "repeat test" key on the test frame cancels the advance 

 of the intertoll trunk test connector. Since the test frame cannot then 

 advance to the next test connector crosspoint, it tests the same trunk 

 repeatedly. This is useful for verifying a trouble condition and for de- 

 tecting an intermittent trouble, or for obtaining data on stability versus 

 time. 



Manual Tests. When the test frame is set up for making manual tests, 

 it engages the office common control equipment to set up a path through 

 the switching train to the trunk to be tested but does not pulse forward 

 code 103 or 104. Instead the attendant can pulse forward the proper 

 code to reach the toll test board at the distant end. This permits dial 

 type trunks to distant offices, not equipped with test lines, to be tested 

 manualh^ 



Code 104 Tests. A 3-position key controls transmission testing. When 

 the key is normal, the test frame makes operational tests. When the key 

 is operated to the transmission and noise position, a two-way transmis- 

 sion loss measurement is made and is followed by a noise check at each 

 end of the trunk. When the key is operated to the transmission only 

 position the noise checks are omitted. The latter position is used when 

 it is permissible to omit the noise checks to save time. When making code 

 104 tests, the test frame sets up and breaks down the test connection in 

 the same way as when making code 103 tests and, while the connection 

 is established, it receives supervisory signals from the far end. Thus 

 most of the trunk operating features, except for ringing, are also checked 

 as an incidental part of the transmission test. Irregularities in the circuit 

 operating features can result in a trouble indication in the same way as 

 when making operational tests. 



Trouble Indications 



During a test, progress lamps display the progress of the test call and, 

 when trouble is detected, one of a number of trouble indicating lamps 

 may also be lighted. The progress and trouble indicating lamps indicate 

 the general nature of the trouble. 



When the Teletypewriter is not in operation, a trouble indication 

 causes the test frame to stop, to hold the trunk busy and to sound an 

 alarm while awaiting the attention of the attendant. It is the usual 

 practice for the attendant to make a repeat test on the same trunk to 



