Technical data

498 Chapter 18
T1 Analyzer
Making T1 Measurements
T1 Analyzer
Sample Loopback CSU Full T1 BERT Test
Use this test mode to perform a measurement, such as BERT, on a known test
pattern being sent from the far end. The far end signal will be generated by looping
back the transmitted signal from this test set. You will use this test set to send a code
to automatically loop-up either a CSU or NIU at the far end. Since a pattern is being
sent on the T1 line, service on the T1 will be affected.
Once you have selected this test mode, you can send the loop-up or loop-down code
using the buttons on the Control menu. If you are you are using ESF, configure the
appropriate ESF Loop Code on the Setup menu.
The T1 circuit is not available for service when using this test mode. End-to-end
loopback tests are normally limited to the CSU since NIU loop codes are normally
suppressed at the central office.
When the far end of a T1 circuit is in a remote location and trouble is suspected, it is
possible to place the equipment at the far end into loopback by sending a special
code designated for this purpose. If the T1 circuit is leased, then the wireless
technician is often limited to looping only the CSU, as NIU loop codes are usually
blocked at the central office. The loop code can be sent either in-band or on the ESF
datalink channel by the test set to the far end equipment. The first method, in-band,
replaces the bits in the T1 traffic channels with the unique loop code. The remote
equipment must see this code for 5 seconds before it will respond in order to
minimize the potential that patterns in live data will falsify this request. The
downside of this technique is that all devices in the transmit path see this code and
any may respond. This could lead to a confusing situation if a T1 route consists of
multiple hops, each with its own CSU pair. If the far end has a hard loop then the
loop code could come back to the near end and inadvertently place that CSU into
loopback. The test set does monitor for a pre-existing loop and will notify you when
remote loopback is attempted using an in-band loop code.
Another method is available if the circuit is designed for Extended Super Frame
(ESF). This method, ESF datalink, sends the loop code on the ESF data link bits.
This method is not prone to false information and, therefore, responds very rapidly.
This is the default mode of the test set. For more information, see the section
23 Inject an error.
a. [Inject]
b. [On]
Causes the error or condition that is currently
displayed on the button to occur.
Step Notes