Twisted Pair Facts

Twisted pair cables support a wide variety of fast, modern network standards. Twisted pair cabling is composed of the following components:

Two wires that carry the data signals (one conductor carries a positive signal; one carries a negative signal). They are made of 22 or 24 gauge copper wiring.
PVC or plenum plastic insulation surrounds each wire. Plenum cable is fire resistant and non-toxic. It must be used when wiring above ceiling tiles. PVC cable cannot be used to wire above ceilings because it is toxic when burned.
Two wires are twisted to reduce the effects of electromagnetic interference (EMI) and crosstalk. Because the wires are twisted, EMI should affect both wires equally and can be cancelled out.
Multiple wire pairs are bundled together in an outer sheath. Twisted pair cable can be classified according to the makeup of the outer sheath:
- Shielded Twisted Pair (STP) has a grounded outer copper shield around the bundle of twisted pairs or around each pair. This provides added protection against EMI.
- Unshielded Twisted Pair (UTP) does not have a grounded outer copper shield. UTP cables are easier to work with and are less expensive than shielded cables.

The table below describes the different unshielded twisted pair (UTP) cable types (categories).

Type	Connector	Description
Phone cable	RJ-11	Used to connect a PC to a phone jack in a wall outlet to establish a dial-up Internet connection. Has two pairs of twisted cable (a total of 4 wires).
Cat 3	RJ-45	Designed for use with 10 megabit Ethernet or 16 megabit token ring.
Cat 5	RJ-45	Supports 100 megabit and ATM networking. Cat 5 specifications also support 100 megabit Ethernet.
Cat 5e	RJ-45	Similar to Cat 5 but provides better EMI protection. Supports 100 megabit and gigabit Ethernet.
Cat 6	RJ-45	Supports 10 gigabit Ethernet and high-bandwidth, broadband communications. Cat 6 cables often include a solid plastic core that keeps the twisted pairs separated and prevents the cable from being bent too tightly. Additional standards for Cat 6 include Cat 6a (advanced) and Cat 6e (enhanced) which provide better protection against EMI.

Each type of UTP cable can be substituted for any category below it, but never for a category above. For example, Cat 6 can be substituted for a task requiring Cat 5e; however, neither Cat 5 nor Cat 3 should be used for this particular task.

The table below describes the two types of connectors used with twisted pair cables.

Connector	Description
RJ-11	Has 4 connectors Supports up to 2 pairs of wires Uses a locking tab to keep connector secure in outlet Used primarily for telephone wiring
RJ-45	Has 8 connectors Supports up to 4 pairs of wires Uses a locking tab to keep connector secure in outlet Used for Ethernet and some token ring connections

Note: When connecting a modem to a phone line, connect the modem to the wall jack using the Line port on the modem. Then connect the phone to the Phone port on the modem. This allows you to use the phone or the modem using a single connection.