Chapter 6. Diagnostics6-8 MX2800 STS-1 User Manual 61200659L1-1STS-1 LOOPBACKSAfter you select STS-1 LOOPBACK, the menu in Figure 6-10appears. The sections following the figure provide descriptions andillustrations of the testing options. Select 1=D ATA M ODE to end atest in progress.Figure 6-10. STS-1 Diagnostics MenuLine NetworkL INE N ETWORK performs a loop of the STS-1 back to the network.This loopback occurs just prior to the HDB3/B8ZS decoder of theLIU; therefore, any coding violations received by the STS-1 will beinserted back into the network without modification. See Figure6-11 on page 6-9 for an illustration of this text.If a LINE N ETWORK loopback is active when the MX2800 STS-1 isoperating in the FREE-R UN timing mode, the timing source for theSTS-1 is effectively removed from the circuit. Therefore, it is up tothe test equipment or network to provide STS-1 timing into thecircuit for the duration of the test.
