ADTRAN MX3216 System Manual page 141

Option Description
3 Digital Loopback
4 Remote Loopback (C-Bit Only)
5 Remote ALL T1 (C-Bit Only)
61189008L1-1B
Table 6-50. DS3 Test Menu Options (Continued)
Section 6, User Interface - Menu Descriptions
Function
This test loops towards the 3/1 cross-connect and
includes the DS3 framer.
This test performs a line loopback at the equipment
on the other end of the selected DS3.
This test performs a tributary loopback on all DS1s
in the DS3 at the equipment on the other end of the
selected DS3.
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