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Chapter 5. Test and Diagnostics
Sub link local analog loop back
The sub link local analog loop back is performed by connecting the sub link transmit signal to
the input of the receive path, as shown in Figure 5-6. This loop back test checks the connection
to the equipment connected to the local sub link. The test signal is provided by the equipment
connected to the local sub link.
LOCAL ETU02-MUX
User
DTE
CH1
CH2
E1
Transmission
CH3
CH4
SUB
LINK
E1
Transmission
MAIN LINK
Figure 5-6. Sub link local analog loop back
Sub link local digital loop back
The sub link local digital loop back is performed by connecting the sub link receive signal to
the output of the transmit path, as shown in Figure 5-7. This loop back is used when testing
from the remote equipment and tests the local ETU02-MUX and the connection to the remote
equipment. The test signal is provided by the equipment connected to the remote sub link.
During this loop back, the ETU02-MUX sub link sends an unframed “all ones” signal to the
equipment connected to the local sub link.
LOCAL ETU02-MUX
User
DTE
CH1
CH2
E1
Transmission
CH3
CH4
E1
Transmission
"1"
SUB
LINK
MAIN LINK
Figure 5-7. Sub link local digital loop back
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