Juniper ACX1000 Configuration Manual page 1386

ACX Series Universal Access Router Configuration Guide
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Any open wire
Wires of a particular pair that are shorted
Distance to fault per pair—Distance at which an open or a short-circuit is detected in
meters. This measurement is also termed as cable length. The transceiver reports the
following faults:
Cable length when the cable status is normal
Distance to fault when the cable status is not normal
Pair Swap—Swapping of twisted-pairs in straight-through and cross-over cable plants
are detected.
Polarity Swap—Each cable pair carries a differential signal from one end to the other
end of the cable. Each wire within the pair is assigned a polarity. The wires in a pair are
normally connected in a one-to-one form. This connection enables the transmitter at
one end to be connected to the receiver at the other end with same polarity. Sometimes,
the wiring within the pair is also swapped. This type of connection is called polarity
swap. Broadcom transceivers can detect such swapping and automatically adjust the
connection to enable the links to operate normally. However, the transceiver reports
polarity swaps that it detects in the cable plant.
On 4-port Gigabit Ethernet and 8-port Gigabit Ethernet MICs with copper SFP transceivers
(using BCM54880) and 4-port Gigabit Ethernet, 6-port Gigabit Ethernet, and 8-port
Gigabit Ethernet MICs with copper and optical SFP transceivers (using BCM54640E
PHY), only 10BASE-T pair polarity is supported. 100BASE-T and 1000BASE-T polarities
are not supported.
When the Gigabit Ethernet link cannot be established (for example, if only two pairs are
present that are fully functional), TDR in the physical layer (PHY) brings down the link
to a 100 MB link, which is called a downshift in the link. The physical layer might require
10-20 seconds for the link to come up if a downgrade in wire speed occurs because it
attempts to connect at 1000 MB five times before it falls back to 100BASE-TX.
TDR diagnostics is supported only on copper interfaces and not on fiber interfaces.
Keep the following points in mind when you configure TDR:
If you connect a port undergoing a TDR test to a Gigabit Ethernet interface that is
enabled to automatically detect MDI (Media Dependent Interface) and MDIX (Media
Dependent Interface with Crossover) port connections, the TDR result might be invalid.
If you connect a port undergoing a TDR test to a 100BASE-T copper interface, the
unused pairs are reported as faulty because the remote end does not terminate these
pairs.
You must not modify the port configuration while the TDR test is running.
Because of cable characteristics, you need to run the TDR test multiple times to get
accurate results.
Do not change the port status (such as removing the cable at the near or far end)
because such a change can result in inaccurate statistics in the results.
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