WAN Module Installation and User Guide
2-9
Monitoring WAN Physical Links
to the remote end. At the remote end, the process is reversed as the framing bits are
discarded and the data stream is passed to the remote system.
Loopback can be enabled on the near-end of a WAN link, but only the T1 and T3
modules can enable loopback on the far-end of a link. The near-end loopback modes are
controlled directly by the hardware on the near-end. Far-end loopback modes require
the cooperation of the far-end hardware. A message is sent to the far-end to cause it to
enter a far-end loopback mode. When loopback is enabled on a WAN port, the green
port LED will blink.
Near-end Loopback Modes
The near-end of T1 links can be enabled for the following three loopback modes:
•
Local
•
Network Line
•
Network Payload
The near-end of E1 and T3 links can be enabled for the following two loopback modes:
•
Local
•
Network Line
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.
Figure 2-2: Local loopback mode
XM_011
Remote WAN Port
Local WAN Port
Framer
Data in
Data out
Data out
Data in
Framer
