NT5D33 and NT5D34 Lineside E1 Interface cards Page 309 of 906
Circuit Card Description and Installation
Figure 60
MMI External loopback test
Test 3, network loopback, loops the LEI's received E1 data back toward the CPE. No test data is generated or received by the LEI. 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 E1 link or the CPE device could be defective. To isolate the failure to the CPE device, tests 2 and 3 must be run in tandem. Figure 61 illustrates how the signaling is looped back toward the CPE.
Figure 61
MMI Network loopback test
E-1 link
Line side
E-1
interface
card
Customer
premise
equipment
(CPE)
Common
Equipment
System
External
network E-1 link
553-1161
E-1 link
Line side
E-1
interface
card
Customer
premise
equipment
(CPE)
Common
Equipment
System
External
network E-1 link
553-1162