Specifications

Chapter 3 Testing & Diagnostics
3-2
LIU has failed, and should be replaced. (Note: Test is valid only with at least one channel
card in place.)
Off: When the Self Test switch is in the Normal position, the Test LED is turned off and the Access
Bank is returned to normal operation.
Note: The Self Test can be turned on and off to reset the Access Bank. This is useful when the user
wants to manually return to normal operation if no loop-down code was sent to the Access Bank
after T1 line testing by a carrier (that is a loop-up code was sent but no loop- down code was sent
after testing, the test LED being yellow).
Access Bank
Self-Test Loopback Network Loopback
T1 Line
Receive Pair
Transmit Pair
Self Test and Network Loopback Block Diagram
NETWORK LOOPBACK SWITCH
Changing this test switch to the Network Loopback position causes the T1 signal received from the T1
line (network) to be sent back toward the T1 line. The function is performed by a connection of the T1
receiver to the T1 transmitter, before the T1 framer chip of the Access Bank. T1 signals are sent back to
the network exactly as they were received. No pulse density enforcement, Bipolar Violation (BPV)
correction, or framing is performed that would corrupt T1 test patterns (such as QRSS) sent from the far
end. Channel interfaces are held in the Trunk Processing state when the Network Loopback switch is
activated. The Test LED shows a continuous Yellow indication while this switch is set to the Network
Loopback position.