Figure 1-4. Network Loopback Tests - ADTRAN TSU LT User Manual

Chapter 1. Introduction
connection. Network and DTE interface loopbacks are
discussed in this section.
Network Loopbacks
There are three types of network loopbacks. See Figure 1-4.
Line Loopback
Loops all of the received data back toward the network. The
transmitted data is the identical line code that was received,
including any bipolar violations or framing errors.
Payload Loopback
Similar to line loopback, except that the framing is extracted
from the received data and then regenerated for the transmit-
ted data.
Data Loopback
Loops back all active DS0s and inserts idle code into unoccu-
pied DS0s.

Figure 1-4. Network Loopback Tests

1202060L2-1 TSU LT User Manual 1-9