 the loopback points that are usually available. Remember that the descriptions are based on the network as seen from Router A in Figure 21-11: Data port/DTE This point loops the signal from the directly connected data device (in our case, Router A) back to that device without using the T1 framer logic. This tests the V.35 cable and the router. Local This point loops the signal from the directly connected data device back to that device after it has been processed by the T1 framer logic. This tests the CSU/DSU, in addition to testing the physical connection to the router. Payload This point loops the signal coming from the T1 back onto the T1 after it has been processed by the T1 framer logic. This test would be administered on the (B) side in our example, but the loopback would be set locally on CSU/DSU (A). This point loops the signal coming from the T1 back onto the T1 before it has been processed by the T1 framer logic, effectively testing the T1 line without testing the CSU/DSU. In our example, a line loopback on CSU/DSU (A) would be tested from the (B) side, though the line loopback would be set locally on CSU/DSU (A). Remote line Remote line loopback is a feature available on some CSU/DSUs that allows a local CSU/DSU to set a line loopback on the far-end device. In our example, though the loopback would exist on CSU/DSU (B), you'd enter the command to initiate the loopback on CSU/DSU (A). Remote payload Remote payload loopback is a feature available on some CSU/DSUs that allows a local CSU/DSU to set a payload loopback on the far-end device. In our example, though the loopback would exist on CSU/DSU (B), you'd enter the command to initiate the loopback on CSU/DSU (A). Say we're having problems with the T1 in Figure 21-11 and we need to troubleshoot. Looking at the error stats in CSU/DSU (A), we see many OOF, BPV, and CRC6 errors. Actual testing of the T1 line would typically proceed as shown in Figure 21-12. First, we set a data port loopback on CSU/DSU (A) and send our tests. The tests all pass without er