934 THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1950 



the code 103 or oode 104 test lines. A steady off-hook signal is returned 

 over the established connection to the test frame at the originating office 

 to indicate that the test may proceed. 



The process of setting up a test call, as described above, simulates 

 very closely the procedures followed in setting up a normal call from an 

 incoming trunk in the originating office to a desired number in the 

 distant office. Therefore, any irregularities in the operational features 

 while setting up the test call will be detected by the test frame and will 

 result in appropriate trouble indication at the test frame at the originat- 

 ing end. 



The automatic testing arrangements aaIU operate with offices where 

 terminating calls are switched either on a terminal net loss (TNL) or 

 on a via net loss (VNL) basis. This is done by including appropriate 

 pads for use at VNL offices. 



FEATURES OF INTERTOLL TRUNK TEST FRAME 



Control of Test Connector 



When the trunk test frame is put into operation, it closes the first 

 crosspoint of the first test connector crossbar switch on the test con- 

 nector frames to prepare for testing the first trunk in the test sequence. 

 When the trunk test is completed, the test frame advances to the next 

 crosspoint for testing the next trunk. This progression continues through 

 all the test connector frames until all intertoll trunks in the office have 

 been tested. The test frame stops when the test cycle is completed. Par- 

 ticular circuit selection keys are provided on the test frame so that the 

 test connector can be directed manually to any point for testing an 

 individual trunk or for starting a test cycle at some intermediate point 

 in the test sequence, rather than with the first trunk. As the test frame 

 progresses through a test cycle, it also displays on lamps a 4-digit "trunk 

 identification number" corresponding to the test connector crosspoint 

 which is closed. When a trouble is encountered, the attendant uses this 

 4-digit luimber to identify the trunk being tested as a particular trunk 

 to a particular destination. The Teletypewriter prints the trunk identifi- 

 cation number as a part of each trunk test record. 



Busy Test 



Before starting a test, the test frame tests the trunk sleeve lead for 

 busy. If the trunk is busy, the test frame waits for the trunk to become 

 idle. A "pass busy" key is provided which, when operated, cancels the 

 waiting period and causes the test frame to immediately pass over busy 



