CAT (5, 6, etc.): Stands for “CATegory” of copper cables used in network and telephone cabling. For a discussion of various types of network cables compared, see Ethernet for more detailed discussion.
Generally: Cat stands for “CATegory” of cables used in network and telephone cabling. Based on the Commercial Building Telecommunications Standard developed by the Electronics Industries Association as requested by the Computer Communications Industry Association in 1985. (See Associations for more.) CAT cable can be manufactured and labeled as either UTP (“Unshielded Twisted Pair”) or STP (“Shielded Twisted Pair”), STP providing less interference and more security, because the greater the number of twists, the safer the signal will be from interference and crosstalk. Cables may also be labeled as either straight (network connections for many devices) or cross-over (connects only two devices directly), but this isn’t usually necessary on most systems. Here’s a summary of the various categories (remember that “x Mbps” is the same as “x Mhz”). Some of these types are in fact “standards” (ISO/IEC [International Organization for Standardization/International Electrotechnical Commission; again, see Associations] standards can be followed anywhere in the world, but are voluntary, giving manufacturers a manufacturing guideline; the category refers to the cable, and the class refers to the connector), others merely a name without any associated standard. In addition to the standards, various federal, state and local codes (which have the effect of law) control the type and installation of cable in the various jurisdictions:
Cat 1 cable (a name, but never an actual ISO standard) was used in the 1950s for doorbell wiring and analog (POTS) phones, at rates up to 1Mbps.
Cat 2 cable (also a name but not a standard), at rates up to 4 Mbps was mainly used for the old IBM Token Ring networks.
Cat 3 cable was used for analog voice (telephone) cable, unshielded twisted pair with 100 ohm impedance at up to 16Mhz frequencies, with only 4 copper wires, terminated by RJ9 connectors. [This type of cable is still found in older structures and not used much any more.]
Cat 4 is basically enhanced Cat 3 cable (at 20 Mbps) for telephone networks and 16 Mbps Token Ring networks. [Also hardly ever found any more.]
Cat 5 is used simultaneously for both computer networks and telephone and consists of 4 pairs of 24 gauge copper wire with 3 twists per inch (reducing electrical interference and crosstalk) terminated by RJ45 connectors, supporting frequencies up to 100 Mhz and speeds up to 1000 Mbps.
Cat 5e is enhanced to support “gigabit” ethernet networks (10/1000BASE-T) at speeds up to 100 Mbps and for long distance (350 meters, vice 100 meters for Cat 5) links.
Cat 6 is suitable for 1000 Base-T up to 100 meters, up to 250 Mbps.
Cat 6e increased the speed to 500 Mbps, supporting 10 Gigabit ethernet networks.
Cat 7 (a/k/a ISO Class F) has four individually-shielded cable pairs inside electromagnetic shielding and is designed for 10-Gigabit network and 600Mhz, but can run up to 1.2 Ghz in pairs when using Siemon connectors (see connectors).
Cat 7A upped the bandwidth to 1000Mhz.
Cat 8 will support 40Gb/s over a two-connector channel up to at least 30 meters, up to 1000Mhz. But it is a completely different channel topology and not just a performance upgrade from the previous numbered cable category. This has created some confusion about the differences between Cat 7, 7A and 8, as 7A may actually have better performance than Cat 8 in many instances. Both Cat7/7A and 8 cable can be used with either RJ or special Siemon TERA connectors, which are completely different than the usual RJ type connector.
Plenum: For office applications, plenum cable is a type of cable often run in the spaces of buildings used for air circulation (HVAC and telephone cables), typically between the structural ceiling and the suspended ceiling or under a raised floor. This type of twisted pair and coaxial cable is coated with a fire-retardent coating (typically Teflon), so that in case of fire it does not give off toxic smoke and gasses as it burns, which can be dangerous to building occupants. [I have read that some [E.G. Black Box] say that differing CATS (e.g. CAT 5e and CAT 6) aren’t compatible on the same network, but I don’t think this is so, although you should always keep a map of the separate runs in case there are problems later on.] Click on the page links below for photos of different ethernet cable and connectors.
Terminations: The most common computer cables (UTP) can be terminated with standard plug and jack connectors or punchdown blocks. The plug is the male connector at the end of a patch cord, and the wall receptacle is the jack. The set is often referred to as an “RJ45,” which is really a telco designation for the “modular 8 pin connector, terminated with a USOC pinout”. The punch down blocks and 66 blocks use IDC connections, with one of two possible “pinouts” designated “A” and ”B” (short for LAN specifications T568A and T568B. Note that the twisted pairs of CAT wires consist of four pairs, each pair with a solid and a striped wire. The striped wire is the “tip” and the solid is the “ring” (see Tip & Ring), referring to the tip of the old 1/4” telephone plug and the ring around the shaft which made the old telephone connections.