Category 5 cable
(Redirected from Cat5)
Categories: Computer networks | Signal cables
Category 5 cable, commonly known as Cat 5, is an unshielded twisted pair type cable designed for high signal integrity. The actual standard defines specific electrical properties of the wire, but it is most commonly known as being rated for its Ethernet capability of 100 Mbit/s. Its specific standard designation is EIA/TIA-568. Cat 5 cable typically has three twists per inch of each twisted pair of 24 gauge copper wires within the cable. The twisting of the cable reduces electrical interference and crosstalk. Another important characteristic is that the wires are insulated with a plastic (FEP) that has low dispersion, that is, the dielectric constant of the plastic does not depend greatly on frequency. Special attention also has to be paid to minimizing impedance mismatches at connection points.
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Usage and wiring methods
Cat 5 cables are often used in structured cabling for computer networks such as Fast Ethernet, although they are also used to carry many other signals such as basic voice services, token ring, and ATM (at up to 155 Mbit/s, over short distances).
Cat 5e cable is an enhanced version of Cat 5 for use with 1000BASE-T (gigabit) networks, or for long-distance 100 Base-T links (350 m, compared with 100 m for Cat 5). It must meet the EIA/TIA 568A-5 specification. Virtually all cables sold as Cat 5 are actually Cat 5e. The markings on the cable itself reveal the exact type.
RJ-45 electrical connectors are nearly always used for connecting category 5 cable. Generally solid core cable is used for connecting between the wall socket and the socket in the patch panel whilst stranded cable is used for the patch leads between hub/switch and patch panel socket and between wall port and computer. However it is possible to put plugs onto solid core cable and some installations save on the cost of patch panels and/or wall ports by putting plugs directly onto the fixed category 5 wiring and plugging them straight into the computers and/or hub/switches.
Straight-through and crossover cable
Straight-through and crossover cables are basically the same Cat 5 cable but with different wirings into RJ-45 connectors.
Straight-through Cat 5 cables are used to connect a computer to a hub or a switch. Straight through cables are also used by some phone system and Token Ring. Although the TIA-568A standard is preferred for new installations, it makes no difference which is used.
Crossover Cat 5 cables are used to connect PC-to-PC, hub-to-hub, switch-to-switch, etc. The general rule of thumb is that if two devices of the same type are to be connected, a crossover cable is used. To make a crossover cable, one end should use the TIA-568A standard and the other end should use the TIA-568B standard. What this does is effectively hard-wire the transmit module of each station to the receive module of the other.
Other categories of network cables
- Cat 1 and Cat 2: 1 Mbit/s cables for transfering voice and low-speed data.
- Cat 3: 10 Mbit/s cables, a well-known variant of Cat 5 cables.
- Cat 4: 20 Mbit/s cables, being phased out in favor of Cat 5.
- Cat 6: defined by the ANSI TIA/EIA 568B-2.1. It is suitable for 1000 Base-T Ethernet up to 100 m.
- Cat 7 cable, with four individually-shielded pairs (ScTP) inside an overall shield, has been proposed as a standard but did not gain its popularity. It is designed for transmission frequencies up to 600MHz, which should enable it to carry 10-Gigabit Ethernet (10GBaseT), but requires a redesigned RJ-45 connector (called a GG45) to achieve this speed. Also in development are standards such as Tera from Siemon. Tera, which does not maintain compatibility with RJ-45, promises transmission frequencies of up to 1200 MHz. 10GBaseT networks are not yet widely available, and may not be able to compete with fibre optic networks.