Network Cable

Network cable (cables and wires)

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Overview of the network cable

Network cables, as their name implies, establish connections between network devices, or between several computers and a scanner, printer or other device activated by computer commands. Different network cables exist for different purposes: some are suitable for relatively short-distance connections and small numbers of other devices, while others are more suited to long distance connection and very large numbers of other devices. The protocol and topology (i.e. the physical, location-based and logical data-flow-based structure) of each network also determines which network cables and wires can be used.

While the uptake of wireless connection technology is growing rapidly, and may well supplant cables and wires in the not-too-distant future, the latter are still extensively in use to enable the transmission of data and signals from one location and device to another.

The main categories of network cable in use today are coaxial cable (or “coax”), twisted pair, fibre optic cables, and Ethernet crossover, terms which will be explained in the “Technical aspects” section below.

 

History of network and wireless technology

The history of network technology can be traced back to 1844, when Samuel Morse (the man who created the famous Morse Code) managed to send a message from Washington to Baltimore, a distance of 37 miles, with his newly-invented Telegraph. The Morse code, a binary language made up different combinations of dashes (“dahs”) and dots (“dits”) to represent the words of the alphabet, is in principal similar to the means of data transfer between modern computers. It was, of course, far slower: just two or three dots and dashes could be transmitted per second, while contemporary computers can transmit their equivalents (1’s and 0’s) at vastly higher speeds and volumes (around 1,000,000,000 per second, or 1 Gigabit per second).

Other inventors experimented with codes made up of more characters in the eighteenth and early twentieth century, notably the French telegraph engineer Émile Baudot with his five-bit code and typewriter style keyboard which was improved by the New Zealand engineer Donald Murray and sold to Western Union. This development led to the replace of Morse Code machines with the new teleprinting system.

The need for more sophisticated means of data transfer prompted a group of US communications firms to collaborate on a new code, which became the 7-bit, 128-character American Standard Code for Information Interchange (ASCII). Instantly, with the exception of IBM, all computer and communications companies across the world adopted it (IBM came on board subsequently after its own code failed to take on, but used a modified version which it called “Extended ASCII”).

By the mid-1970s, the demand for faster and more sophisticated methods of data transmission and sharing grew even stronger, leading the Xerox Organisation to develop Ethernet technology, which was standardised in 1979 with the assistance of Intel and DEC. This new system could transmit data at the rate of 10 Megabits per second, an unprecedented speed at that time. It required connection using exceptionally thick coaxial cable, which would have to be run throughout the building in which different devices were to be linked together into a Local Area Network (LAN). The cable, known as 10Base5 (or simply “Thick Coax”) was so named because its speed was 10 Mbps, it used its entire bandwidth for every data transfer and its maximum length was 5 decimetres (500mm). Unlike base band cables, broadband cables can divide their bandwidth into a number of distinct channels, allowing several different streams of data to be transmitted simultaneously.

The so-called “Thin Ethernet” or 10base2 was released in 1985, although the “2” is slightly misleading as the actual maximum length of cable was 1.85dm (180mm). Two years later, twisted pair cabling began to take on for making Ethernet connections, leading the Institute of Electrical and Electronic Engineers (IEEE) to release a new Ethernet standard in 1990, the 10baseT (where ‘T’ refers to twisted pair).

Structured cabling systems based on Unshielded Twisted Pair (UTP) cables (see below) began to appear in 1991, and higher grades of UTP cable began to be used in 2000, with data rates of between 20MHz and 100MHz.

Discounting primitive wireless technology such as smoke, firelight and flag signalling in the first centuries AD, the first wireless communication device was the optical telegraph invented by Claude Chappe in the eighteenth century. In 1936, a voice and video broadcast was made between Berlin and Leipzig, but true wireless technology capable of modulating electromagnetic waves was not developed until well after the discovery of the latter by Michael Faraday and Joseph Henry in 1831. In 1886, Heinrich Hertz demonstrated the wave nature of electrical transmissions through space, but the name most prominently associated with wireless technology is of course that of Guglielmo Marconi who provided the first demonstration of wireless telegraphy in 1895. The world’s first transatlantic transmission occurred in 1901, with commercial transatlantic connections in place by 1906.

By 1911, the first mobile transmitter appeared on board the Zeppelin and in 1915, the first wireless voice transmission between New York and San Francisco was set up. Marconi’s discovery of radio short-waves made an enormous difference, as they were naturally reflected at the ionosphere. In 1933, FM wireless transmission was introduced and proved to be vastly superior in quality to the pre-existing AM.

In 1971, the first Wireless Local Area Network connecting seven computers was developed by Norman Abramson at the University of Hawaii (which also gave it its name – the “Alohanet”). WLAN is now in its third incarnation, capable of transmitting data at the rate of 2Mbps.

Mobile wireless communication took a major leap forward in 1982, when the countries of the European Union developed a new EU-wide, fully digital, 900 MHz mobile phone standard.

 

Technical aspects

A set of technical and quality standards govern the installation and design of structured network cabling for voice and data transmission according to whether it is installed in domestic units such as apartments, in offices or in data centres. The most prevalent are twisted pair cables designated as either CAT-5e (category 5e, capable of 100MHx performance) or CAT-6 (category 6, capable of 250 MHz performance). Fibre optic cabling is also increasingly established. All eight of the conductors inside these cables are connected, so that none is used for dual purposes such as voice and data transmission.

The standards prescribe the topology of cable runs and typically include the use of a central patch panel to which various modules can be connected. Every outlet from this panel is linked either to a network switch, an internet provider or private branch executive telephone exchange.

Patch panel cables are normally colour coded for ease of identification.

How the network cable differs from other cables and the difference between different network cables

Coaxial cables consist of a central single-wire copper conductor ensheathed in an electrically insulating (dielectric) plastic coating, which is itself encased throughout the length of the cable in a metallic mesh shield. The cable is then coated in a final layer, the plastic jacket, which can be either thick or relatively thin. Within limits, these cables can be twisted or bent without becoming damaged, although the thicker the external plastic jacket, the less pliable they become. They are typically used for signals requiring bandwidths of several MHz such as television.

Twisted pair cables consist of two conductors which are literally twisted together into a double helix. They are highly suited to telecommunications devices such as telephones because their design tends to cancel our electromagnetic interference from other devices and prevent undesirable effects such as telephone crosstalk. There are three main types of twisted pair cable – foil, unshielded and shielded. Unshielded Twisted Pair (UTP) cable is widely deployed in Ethernet networks.

The central glass filament within fibre optic cables is protected by several layers of material, before a final coating of PVC or Teflon is added, chiefly to minimise interference. Although they remain costly, their chief advantage is that, with their much greater bandwidth, they can transmit large quantities of data over very long distances.

Ethernet crossover cables dispose of the need for routers and network switches when connecting several computers together. Computers can simply be connected via their integral Network Interface Cards (NICs) instead.