RJ-45 Wiring and Cables
RJ-45 connectors are used for the following ports:
-
Console
-
Asynchronous
-
Auxiliary
No standards define RJ-45 interface pinouts, but Cisco defines
them as DTE. If you were to cable the access server port (RJ-45) to an external
device (modem or terminal), you would need RJ-45-to-RJ-45 cable and an
RJ-45-to-DB-25 adapter. An RJ-45-to-RJ-45 cable can be rollover or
straight-through. A rollover cable has its pins reversed, as in 1 to 8, 2 to 7,
and so on. A straight-through cable, on the other hand, has the pins going
straight in a 1 to 1, 2 to 2 fashion.
To find out which of the two types of cable you have, hold the
two connector ends of the same cable side by side. Check the color-coded wires
inside the connector. Straight-through cable wires are the same color for the
same pins on both connectors. A rolled cable has the wire colors on the two
connectors flipped, as shown in Figure
3-1.
The octal cable used for the asynchronous port connections
functions as a rolled cable.
An RJ-45-to-DB-25 adapter can be either rollover or
straight-through. For instance, a male or female DTE adapter (MDTE or FDTE) is
straight-through. A male or female DCE adapter (MDCE or FDCE) is rolled. A male
modem (MMOD) adapter is rolled and is the only one that supports modems. In it,
the MDCE connectors are changed so that DB-25 pin 8 instead of pin 6 is wired to
DSR.
The auxiliary and console ports are configured as DTE devices
on Cisco access servers. Terminals (such as PCs) are also DTE devices. Two DTE
devices cannot be directly connected unless the signals are rolled exactly once.
So you must either roll the pins in the cable or in the DB-25 adapter, but not
both. To directly connect two DTE devices, you can use either of these
formulas:
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