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Quantum and Evolution Series Installation and Operating Handbook
Options:
Off
Interface
Interface (local and remote)
Framer/deframer (local)
RS (local)
FEC (local)
IF (local)
Factory default:
Off
Allows a number of loopbacks to be selected to aid fault diagnosis and
Description:
resolution of system level problems.
IF (local) is used to loopback transmit to receive internally within the
modem.
Interface (local and remote) is used to loopback receive to transmit and
is normally set on one of the pair of modems (usually the remote
modem).
The other modems are more specialized and cause a loopback at
various points within the Tx/Rx processing chains.
In general it is not a good idea to loopback IP data to itself. This will
cause the modem to retransmit on its terrestrial port packets that it has
received and this can confuse intelligent switches, which conclude that
the original sending device has moved and is now on a different port,
which can cause traffic storms! If it is necessary to test modems that
have an IP interface, it is recommended to change the terrestrial
interface selected to be a serial interface (which is fitted on all modems)
and to perform the loopback test and then change the interface back to
IP.
7-159
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