MX2800 STS-1 User Manual Loopbacks, Section 6VT/Port Loopbacks61204659L1-1A 6-5CSU LoopbackA CSU Loopback enables the MX2800 STS-1 to generate a CSU loopback pattern (001001…) toward theT1 CSU for six seconds. After six seconds have elapsed, the pattern will cease and incoming networktraffic will be passed through to the CSU device. If the CSU device successfully responded to the CSUloopback pattern, it will return all data back toward the network. When Data Mode is selected, aloop-down pattern (0000100001….) will be generated toward the CSU for six seconds.NOTEWhen in CSU Loopback, only the Data Mode for the T1 under test maybe selected. Selecting any other option will result in an error message.CSU Loopback w/BERTA CSU Loopback w/BERT enables the MX2800 STS-1 to test the local T1 loop to the CSU using thestandard QRSS pseudo-random bit sequence. When CSU Loopback w/BERT is selected, the MX2800STS-1 will initiate a CSU loopback pattern toward the CSU attached to the selected T1 line similar to theCSU Loopback test above. Six seconds after starting the CSU loopback pattern, the MX2800 STS-1 willcease sending the CSU loopback pattern and begin sending an unframed QRSS pattern toward the CSU. Ifthe CSU device successfully responded to the CSU loopback pattern, it will return all data back toward thenetwork. The MX2800 STS-1 will check the incoming pattern for errors. Additional menu items willappear to show the state of pattern synchronization, error count, and a clear error count option (see Figure6-7). Selecting Data Mode will cease the transmission of the QRSS pattern and start transmission of aloop-down pattern as previously described.NOTEOnly 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 CSULoopback, CSU Loopback w/Bert, or Line Bert is selected, the formertest will be terminated and the latter test will be engaged.Figure 6-7. Loopback Menu with BERT Selected
