Chapter 1. Introduction1-6 ESU LT User Manual 61200410L1-1run during normal operation to confirm continued correctfunctioning. The background tests include:• Monitoring the phase-locked loop for lock.• Standard background network performance monitoring.Loopback TestsA number of different loopbacks can be invoked locally fromthe front panel, by T-Watch commands, or remotely usingV.54 loopback code.Network LoopbacksThere are two types of network loopbacks. See Figure 1-4.Payload LoopbackSimilar to line loopback, except that the framing is extractedfrom the received data and then regenerated for thetransmitted data.Line LoopbackLoops all of the received data back toward the network. Thetransmitted data is the identical line code that was received,including any bipolar violations or framing errors.Figure 1-4. Network Loopback TestsESUE1
