Unit installation

FCD-E1 Installation and Operation Manual Chapter 6 Troubleshooting and Diagnostics
Testing FCD-E1 6-21
Channel Local Loopback (LP LOC CH)
Local digital loopback towards the local user DTE connected to the channel on
which the loopback is connected. Performed by connecting the data channel
transmit signal to the input of the receive path, as shown in Figure 6-6. The test
signal is provided by the local DTE, which must receive its own transmission. This
test mainly checks the connections to the local DTE.
When an alarm condition is present on the main link, the receive data is held at
MARK. Under these conditions, it is not possible to perform BER measurements
when a local channel loopback is connected. If you try to measure BER, the result is
invariably errors.
LOCAL FCD-E1
E1 Sub
DSU
LTU
User DTE
Figure 6-6. Channel Local Loopback
Channel Remote Loopback (LP REM CH)
Local digital loopback towards the remote user's DTE connected to the channel on
which the loopback is connected. Performed by connecting the local data channel
receive signal to the data channel transmit input, as shown in Figure 6-7. The test
signal is provided by the remote user DTE, that must receive its own transmission.
This test fully checks the user data link, including the cables connecting the remote
DTE to the FCD-E1, the remote FCD-E1, the transmission plant connecting the
two FCD-E1 and the local FCD-E1.
Transmission
Plant
User DTE
REMOTE FCD-E1
E1 Sub
DSU
User DTE
LOCAL FCD-E1
E1 Sub
DSU
LTULTU
Figure 6-7. Channel Remote Loopback
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