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TESTS
DS1 Test Loopback
Function
AIS
EQUIPMENT
4-6
The DS1 Test Loopback (TLB) function, illustrated in Figure 4-4, allows
the signal received from the network to be looped through as much as is
practical of the CSU's circuitry and transmitted back toward the network.
This tests everything on the network side up to and including the CSU.
When the CSU is in the ANSI mode, framing is regenerated; when it is
in the AT&T mode, framing is not regenerated. Bipolar violations are
corrected in both modes. While the TLB function is active, the CSU
transmits an Alarm Indication Signal (AIS) toward the equipment.
The TLB function can be activated and deactivated locally via the Super-
visory terminal, or remotely via loopback codes as defined
PUB 54016 (for Extended Superframe Format).
To allow remote activation and deactivation, the TLB function must be
enabled via the Supervisory terminal or option switches S5-6 and S6-8.
In ANSI terminology, activation of this function is
equivalent to Payload Loopback (PLB), described in
Bellcore TR-TSY-000194. In AT&T terminology, it is
equivalent to DTE Loopback (DLB).
The TLB function cannot be used alone, but must be used in conjunction
with one of the following tests: DS1 Test Loop, DS1 Remote Test, or DS1
Remote Test with Self-Test.
CSU
FIGURE 4-4. DS1 TEST LOOPBACK FUNCTION
NOTE
T1
NETWORK
in
EQUIPMENT
CSU
AT&T
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