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Diagnostics
Far-End Loopback
When a port of the QUAD DATA module is routed to another QUAD
DATA module or any type of CSU/DSU that supports industry
standard DSU loop codes—far-end loopbacks are supported. When
the Fn) command is used, the QUAD DATA module transmits a
loopback request for a fixed period of time (a few seconds).
While it is sending the loopback code, the module monitors the
receive data for that port. Under ideal circumstances, the QUAD
DATA module transmits the test pattern for a few seconds, the farend device enters a loopback state, and then the QUAD DATA
module briefly receives its own loopback code. This will not
always occur, but if the QUAD DATA module does detect that it is
receiving its own loopback request, it “knows” that the far-end
loopback was successful and indicates this on the third line of the
Diagnostics Menu. See Figure 4-3.
Figure 4-3
DTE
Far End Loopback
Quad Data
CSU or
M1-3
Far End
CSU or
M1-3
Data Port
DTE
Therefore the presence of “yes” for the Far-end loopback field
indicates that the QUAD DATA module has detected a loopback.
The presence of “no” on the Far-end loopback field only indicates
that the QUAD DATA module did not detect a loopback. It does not
necessarily mean that no loopback exists. If a loopback has been
initiated by a far-end operator or network service provider, it will
not be indicated in the Far-end loopback field.
DTE as Test Set
In addition to the tests built in to all Verilink products, many types
of Data Terminal Equipment will indicate received errors and
detected loopbacks. Often this equipment operates using a
protocol which is transparent to the Verilink hardware and may
provide additional performance information. By using loopbacks in
conjunction with the information provided by the DTE, problems
can often be located and corrected. A suggested troubleshooting
procedure follows.
1. Connect to the DTE which is reporting errors. Establish a local
Data Port Loopback and observe whether the errors clear.
Verilink QUAD DATA User Manual
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