Nortel Circuit Card Installation Manual page 243

Figure 34
MMI local loopback test
Common
Equipment
Figure 35
MMI external loopback test
System
Common
Equipment
NT5D11 and NT5D14 Lineside T1 Interface cards
System
Line side
T-1
interface
card
Test 2, external loopback, assumes an external loopback is applied to the T1
link. Test data is generated and received by the lineside T1 card on all
timeslots. If test 1 passes but test 2 fails, it indicates that the T1 link is
defective between the lineside T1 card and the external loopback location. If
test 1 was not run and test 2 fails, the T1 link or the lineside T1 card could be
defective. To isolate the failure to the T1 link, tests 1 and 2 must be run in
tandem. Figure 35 demonstrates how an external loopback is applied to the
T1 link.
Line side
T-1
interface
card
Test 3, network loopback, loops the received T1 data back toward the CPE
equipment. No test data is generated or received by the lineside T1 card. If
test 2 passes but test 3 fails, it indicates that the CPE device is defective. If
test 2 was not run and test 3 fails, the T1 link or the CPE device could be
defective. To isolate the failure to the CPE device, tests 2 and 3 must be run
External
T-1 link
network
External
T-1 link
network
Circuit Card
Page 243 of 906
Customer
premise
T-1 link
equipment
(CPE)
Customer
premise
T-1 link
equipment
(CPE)
Description and Installation
553-AAA1120
553-AAA1121