MX2800 STS-1 User Manual Loopbacks, Section 6
VT/Port Loopbacks
61204659L1-1A 6-5
CSU Loopback
A CSU Loopback enables the MX2800 STS-1 to generate a CSU loopback pattern (001001…) toward the
T1 CSU for six seconds. After six seconds have elapsed, the pattern will cease and incoming network
traffic will be passed through to the CSU device. If the CSU device successfully responded to the CSU
loopback pattern, it will return all data back toward the network. When Data Mode is selected, a
loop-down pattern (0000100001….) will be generated toward the CSU for six seconds.
NOTE
When in CSU Loopback, only the Data Mode for the T1 under test may
be selected. Selecting any other option will result in an error message.
CSU Loopback w/BERT
A CSU Loopback w/BERT enables the MX2800 STS-1 to test the local T1 loop to the CSU using the
standard QRSS pseudo-random bit sequence. When CSU Loopback w/BERT is selected, the MX2800
STS-1 will initiate a CSU loopback pattern toward the CSU attached to the selected T1 line similar to the
CSU Loopback test above. Six seconds after starting the CSU loopback pattern, the MX2800 STS-1 will
cease sending the CSU loopback pattern and begin sending an unframed QRSS pattern toward the CSU. If
the CSU device successfully responded to the CSU loopback pattern, it will return all data back toward the
network. The MX2800 STS-1 will check the incoming pattern for errors. Additional menu items will
appear to show the state of pattern synchronization, error count, and a clear error count option (see Figure
6-7). Selecting Data Mode will cease the transmission of the QRSS pattern and start transmission of a
loop-down pattern as previously described.
NOTE
Only one T1 port may engage a CSU Loopback, CSU Loopback w/Bert,
or a Line Bert. If one of these tests is already active at the time a new CSU
Loopback, CSU Loopback w/Bert, or Line Bert is selected, the former
test will be terminated and the latter test will be engaged.
Figure 6-7. Loopback Menu with BERT Selected
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