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VDV CABLES

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The Cabling

The choice of network cabling (or communication medium as it is sometimes called) is rather important because of the extremely high frequencies of the signals. Sending a 60-cycle utility power through a wire rarely presents a difficulty; but sending 100 million bits per second signal can be a little trickier. For this reason, the method of sending signals and the materials they are sent through can be important.

Network Cabling Types

A number of cabling options are available for networking connections.

Unshielded Twisted pair (UTP)

UTP cable is the primary cable used for networks, as specified in the EIA/TIA 568 standard. This cable type has been widely used because it is inexpensive and simple to install. Limited bandwidth (which translates into slower transmissions) has pushed development of new cable grades (the "categories" of 568) but has created a more expensive product and more complicated installation process.

Screened Twisted pair (ScTP)

Same as UTP with an overall shield around the 4 pairs. While not currently specified for any networks, it is allowed in the EIA/TIA 568 standard, it is used in many networks in Europe where EMI is a greater concern. It tends to be more expensive, harder to terminate and requires special plugs and jacks.

Shielded Twisted Pair (STP)

Like UTP but with a shield around every pair. Widely used in IBM systems (IBM Type 1 cable) and included in 568.

Coaxial Cables

Original Ethernet, used in CATV systems. This is familiar and easy to install, has good bandwidth and lower attenuation but more expensive, bulky. Not included in 568, but in 570 for residential use.

Optical Fiber

Optional for most networks, top performance, excellent bandwidth, very long life span, excellent security but slightly higher installed cost than twisted pair cables, more expensive electronics interface to them. Fiber can be cost effective with optimal architecture.

Other transmission options:


Wireless - no data transmission cable is required to connect any individual terminal, but requires cabling to every antenna (called an Access Point), so it's hardly "wireless". Within the range of the radio signals, a terminal can be moved anywhere. Usually more expensive but used in locations where is would be difficult to install cables. In the modern network, wireless is a requirement because so many users want "mobility" - so they are not "tethered" to a desktop.

Infrared Transmission - Also transmits without wires to the terminal by using inferred (IR) light but each transmitter requires cabling. By sending pulses of infrared light in the same patterns as electronic pulses sent over cables, it is possible to send data from one place to another. Networks based on IR transmission have been developed for use in office and for line-of-sight transmissions between buildings.

Because networking evolved over several decades, many different cabling solutions have been used.

Unshielded Twisted Pair

Because networking evolved over several decades, many different cabling solutions have been used. But today, virtually all VDV copper cabling has moved to unshielded twisted pair (UTP) as specified in the EIA/TIA 568 standard because it has been inexpensive, may already be in place, is familiar to installers and is simple to install. (The cost and simplicity of installation has changed a bit, however, with Cat 6, see below.)
Virtually all VDV copper cabling has moved to unshielded twisted pair (UTP) as specified in the EIA/TIA 568 standard because it has been inexpensive, may already be in place, is familiar to installers and is simple to install.

UTP cable is comprised of four pairs of carefully twisted pairs of copper wire, insulated with carefully chosen material to provide high bandwidth, low attenuation and crosstalk. UTP cable works so well because it is used with transmitters that work on "balanced transmission." They transmit equal but opposite signals on each wire of the pair so each wire has only half the amplitude of the final signal. The electrical and magnetic fields of each wire are opposite and cancel out each other, producing low electromagnetic emissions. Likewise, electromagnetic pickup is the same on both wires so they cancel out.