Description of Test Lines

Test line and test termination are terms sometimes used interchangeably to designate testing equipment, facility, circuit, or testing communication channel. These include simple passive terminations and relatively complex testing circuits capable of applying marginal signaling tests, transmission tests, and recognizing and replying to specific signals received.

Trunk test lines return off-hook (answered) supervision. This permits measurements to be made in the normal "in-service" (talk) condition.

Test lines are adjusted to provide correct level and impedance as measured at their actual switch appearance.

Test lines are reached by dialing a customer-type telephone number when testing toward a class 5 office, or by dialing from 3 to 7 digits when testing toward a toll (class 0-4) office.

NOTE: Test line directories are organized strictly by NPA-NXX relative to the serving switch, there may be test lines located in class 5 offices in adjacent bordering states that are, or are NOT within your local service area.

Class 5 office test lines are arranged to trip machine ringing and may furnish timed disconnect features when joint-holding and/or in-band signaling is used. Line equipment is arranged for terminating service only.

The 10X (ten X) codes are reserved system wide for assignment to special purpose test lines. If the function of a test line is equivalent to that of a test line assigned to 10X code, it is described as a "10X-type".

Following in a description of the various test lines:

Earlier versions are not equipped with timed test tone and may return repetitive 1 second intervals of on-hook every 10 seconds until released.

Fixed PADs (TP2, TP9) and PAD switching signals are included in the test line, when required, to furnish proper reference level at switch.

Trunk A is directed to port A and a far-near measurement is made and recorded. With port A held, trunk B is directed to port B. This loops the far end transmission paths of A and B.

A reference tone is transmitted near-far over trunk B and measured as far-near over trunk A. The first recorded measurement subtracted from the second measurement indicates the near-far loss of trunk B.

Early versions may not be equipped with reference tone, and the initial far-near measurement must first be ascertained from a 102-type test line. Also, some early versions do not trip ringing on port A until port B is seized.

NOTE: All loop-around test lines should be equipped with 60A control units.

After ringing signal and pretripping test, a 1.3 second synchronizing pulse (off-hook signal) is sent. This synchronizes the automatic progression test equipment in the originating office with the test line.

The synchronizing pulse is followed by three 0.2 second pulses of on-hook, separated by 0.3 second intervals of off-hook. During the off-hook periods, soak current is applied; during the on-hook periods, an open circuit is presented to the supervisory relays.

A third series of signals may be provided to test transfer features of Centrex offices.

Results of tests are as follows: 0.3 second bursts of audible ringing at 0.2 second intervals indicate that the trunk tripping feature operated on the pretripping tests, or a tick-tone at 120 IPM, without flash, indicates that all tests are completed.

In offices also equipped with synchronous test line, the nonsynchronous test line may trip ringing, and return alternate 0.5 second off-hook and on-hook signals, with low tone applied during the off-hook period, until released.

The level, as read at the customer location on a 24-type loop checker, will be substantially flat. This enables an "in the green" acceptance of the transmission quality of the loop.

The loop checker test line is not used for trunk testing. On-hook supervision is a standard arrangement.

NOTE 1: Operational test lines do not interwork with SS7

Operational test lines (signal-supervisory test line 103, synchronous, and nonsynchronous) are not functional when the terminating route uses SS7 trunk signaling. SS7 requirements documents have not provided for such test lines (because operational test lines are designed for "per trunk signaling," which requires E&M off- and on-hooks -- in SS7 all signaling is done in the separate SS7 path). This can be confusing when trying to isolate a problem, because testers often use operational test lines for call-through tests; if you are in office 'A', and you are testing through office 'B' (a tandem) to office 'C', even if your route to office 'B' is not SS7 the distant route from 'B' to 'C' might be, and a failure (the call goes either to "fast busy" (120 IPM) or reorder announcement) can be misleading. The thing to remember is that if you are doing any sort of call-through it is best to use milliwatt or similar test line, unless you are certain the route does not include SS7.