3Com 3C509B User Manual page 112

B
When you work with 10BASE-T cabling, concentrators,
and NICs from different vendors, it is possible to connect
everything but still have no communication between
file servers and workstations.
When there are several unknown variables, it is difficult
to determine which component is failing. Start with
the following procedure to narrow the range of
possible causes:
1 Determine whether your equipment complies
with the 10BASE-T standard.
This is particularly important for data concentrators
(hubs or repeaters).
2 Connect a straight-through cable from the PC to
the hub.
The hub performs an internal crossover so that the signal
can go from TD+ to RD+ and TD– to RD–. When you look
at an RJ-45 connector from the front (that is, the opposite
side from where the wires enter the connector), pin 1 is
identified on the right side when the metal contacts are
facing up.
3 Make sure that the TD+ and TD– wires are twisted
together, and that the RD+ and RD– wires are
twisted together.
Using wires from opposing pairs can cause signals to
be lost.
C
ROSSOVER
T
ROUBLESHOOTING
C
ABLE
T
IPS