3-2 CHAPTER 3: CABLING SWITCH 3900 PORTS
Fast Ethernet Ports
Your Switch 3900 has 24 or 36 10/100BASE-TX ports
with RJ-45 connectors. This section contains
information on cabling the 10/100BASE-TX (RJ-45)
ports and pin assignments for the RJ-45 connectors.

Cabling 10/100BASE-TX (RJ-45) Ports

The Switch 3900 system’s Ethernet ports are shielded
RJ-45 data sockets. You can connect shielded or
unshielded data cables with shielded or unshielded
jacks to these data sockets.
The Ethernet ports are numbered from 1X to 24X or
1X to 36X, depending on your system. They are
configured as MDI-X for direct connection to a
workstation or other data terminal equipment (DTE),
using straight-through twisted-pair wiring.
To connect a Switch 3900 system to a
10/100BASE-TX repeater or switch, use a crossover
cable, or set the port on the connected device to MDI
and use a straight-through cable.
Follow these guidelines when you cable
10/100BASE-TX connectors:
■Use two twisted-pair wires for each link.
■Use twisted-pair wire that is 22-26 AWG (0.5
millimeter) in diameter.
■Use twisted-pair wire with an impedance of
between 85 and 115 Ohms.
■Verify that the length of the twisted-pair link from
the system to any potential workstation location is
100 meters (328 feet) or less.
To cable a 10/100BASE-TX (RJ-45) port:
1Remove the dust cover and save it for future use.
2Plug the male RJ-45 connector on the
10/100BASE-TX cable into the selected port until it
clicks into place.
3Attach the other end of the cable to an MDI port on a
workstation, repeater, or concentrator.
4Repeat steps 2 and 3 for the remaining ports.