Airvana ipBTS C30, Installation And Commissioning Manual

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Chapter 4
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RN commissioning
Performing Loopback tests
4-14 910136 Rev01.00 Standard July 2007
The extent of the loopback test (the amount of equipment and cabling that is tested) depends on
where the physical loop back is installed. The farther away from the ipBTS C30 the loopback
is installed, the greater the extent of the test, although Ethernet loopbacks cannot be installed at
the far side of a router, switch, FRAD, or other edge device.
NOTE
If a loopback is installed directly on the backhaul, a bare minimum is tested. For example,
the backhaul cable exiting the ipBTS C30 is not tested.
Airvana recommends installing the loopback at least as far as the far end of each backhaul
cable exiting the ipBTS C30. Installation at that point includes the backhaul cable’s wiring into
the Ethernet port and the backhaul cable itself.
Maximum cable lengths must be considered when installing loopbacks. Loopbacks double the
length of a cable (the cable length now equals the outgoing leg plus the return leg, or twice the
physical cable length). Failure to consider this factor can result in failed loopback tests for
cables that are flawless.
The technician must have appropriate equipment and materials for installing and performing
loopbacks.
Ethernet loopbacks
The Ethernet loopback test has two parts:
• Physically loopback the Ethernet
• Run the loopback test
The loopback can be done externally on the cable or on the Ethernet port by physically
connecting the receive wires (RXs) to the transmit wires (TXs). The loopback can also be done
internally on the hardware transceiver chip. Looping back internally on the transceiver chip
only tests limited hardware functionality and does not test the cable connection or the Ethernet
port. Looping back externally tests more. The Ethernet loopback test is not a standard function
of Ethernet, but is a value-added proprietary feature.
Looping back Ethernet backhaul links
This section explains how to install the physical loopbacks when Ethernet backhaul links are
used. Install the loopback as far as possible along the length of the Ethernet. This increases the
extent of the test. You cannot loopback the Ethernet at the far side of most network devices,
including switches, routers, and FRADS. However, if the Ethernet backhaul cable is connected
to a patch panel (or another passive, pass-through device), you can install the loopback at the
far side of it and thereby include the patch panel in the test.
Because Airvana does not specify the Ethernet cable/connector types, the details of looping
back the Ethernet cables are site-dependent. Typically, Ethernet backhaul cables installed into
the backhaul punch block have an RJ-45 jack at the far-end. This section provides the pin-out
for the RJ-45 jack.