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Chapter 1. Introduction
In addition to the specified self-tests, background tests are run on var-
ious parts of the internal electronics. These run during normal opera-
tion to confirm continued correct functioning. The background tests
include:
•
Monitoring the phase locked loop for lock
•
Standard background network performance monitoring, as re-
quired by ANSI T1.403 and AT&T 54016 for which the results are
stored
Loopback Tests
A number of different loopbacks can be invoked locally from the front
panel or remotely by using special inband codes (AT&T D4 network
loop up/loop down codes and V.54 loop up/loop down codes for the
Nx56K/64K serial interface). Additionally the loopbacks can be re-
motely controlled by out-of-band commands via the T1 ESF facility
data link (FDL), or from T-Watch via a modem connection. Network
and DTE interface loopbacks are discussed in this section.
Network Loopbacks
There are three types of network loopbacks; see Figure 1-4 on page 1-9.
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.
1-8
TSU ACE User Manual
61200295L1-20
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