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206208-A
B-3
The Model 5625HD switch module receives data on pins 1 and 2 and transmits its
data on pins 3 and 6. The host module ports implement this MDI standard
crossover internally and are called MDI-X (the X for crossover), as shown in
Figure B-1
. All Model 5625HD switch module 10BASE-T ports are MDI-X
standard.
Two simple rules govern all usual RJ-45 connections from each Model 5625HD
switch module 10BASE-T/100BASE-TX port to the 10BASE-T/100BASE-TX
port on another device:
• A straight-through cable (MDI to MDI-X) is customarily used for connection
to a station NIC, to a transceiver, or to a cable plant patch panel.
• A crossover cable or adapter (MDI-X to MDI-X; as shown in Figure B-2
) is
customarily used for connection to another switch or hub port.
Figure B-2. MDI-X to MDI-X External Crossover (RJ-45 Example)
Making the crossover externally with a crossover cable or adapter that exchanges
the TD and RD wire pairs (as shown in Figure B-2) is possible but has the
following disadvantages:
• Because a crossover cable is not standard, you might have to specially order
one or make your own.
• Having crossover cables and standard cables that resemble one another in a
network invites confusion.
Caution:
Make any crossover cable you use look obviously different from
normal straight-through cables and put a tag on each end; for example, use a
distinctive color like yellow and put a tag labeled “X-over” on each end.
2007.4
MDI-X port MDI-X port
1
2
3
6
Receive
Transmit
1
2
3
6
Receive
Transmit
Twisted
pairs