Extreme Networks WM-4T1i WAN Installation And User Manual page 26

Configuring the WAN Physical Link
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.
Local WAN Port Remote WAN Port
Data out
Data in
Data in
Data out
Framer Framer
XM_012
Figure 2-3: Network line loopback mode
Network Line Loopback Mode. When the local port is enabled for network line
loopback mode, the received signal is sent back to the remote end without reframing
the data. This mode primarily tests the integrity of the line from the remote side.
Local WAN Port Remote WAN Port
Data out
Data in
Data in
Data out
Framer Framer
XM_013
Figure 2-4: Network payload loopback mode
Network Payload Loopback Mode. When the local port is enabled for network
payload mode, the framer removes the framing bits from the received signal and
recovers the transmitted data. This same data is then reframed and transmitted back to
the remote end. This mode tests the line and the local circuitry from the remote side.
2-10 WAN Module Installation and User Guide