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Monitoring T1 Physical Link
Near-end Loopback Modes
The near-end of the link can be enabled for the following three loopback modes:
• Local
• Network Line
• Network Payload
The local loopback mode reflects the data stream internally to the near-end. The
network line loopback mode reflects the signal to the far-end. The network payload
mode reflects the data carried in the signal and regenerates framing information back to
the far-end.
Local T1 Port
Remote T1 Port
Data out
Data in
Data in
Data out
Framer
Framer
XM_011
Figure 2-2: Local loopback mode
Local Loopback Mode. When the local port is enabled for local loopback, the local
data stream goes into the framer and the framing bits are inserted into the data, but the
data is not transmitted to the remote end. Instead, it is sent back through the local
framer, the framing bits are discarded, and the original data is returned. This mode tests
the local end.
WM-4T1i Module Installation and User Guide
2-7
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