Physical media refers to the physical materials that are used to store or transmit information in
data communications
Data communication, including data transmission and data reception, is the transfer of data, signal transmission, transmitted and received over a Point-to-point (telecommunications), point-to-point or point-to-multipoint communication chann ...
. These physical media are generally physical objects made of materials such as
copper
Copper is a chemical element; it has symbol Cu (from Latin ) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkish-orang ...
or
glass
Glass is an amorphous (non-crystalline solid, non-crystalline) solid. Because it is often transparency and translucency, transparent and chemically inert, glass has found widespread practical, technological, and decorative use in window pane ...
. They can be touched and felt, and have physical properties such as weight and color.
For a number of years, copper and glass were the only media used in computer networking.
The term physical media can also be used to describe
data storage
Data storage is the recording (storing) of information (data) in a storage medium. Handwriting, phonographic recording, magnetic tape, and optical discs are all examples of storage media. Biological molecules such as RNA and DNA are con ...
media like
records,
cassettes,
VHS
VHS (Video Home System) is a discontinued standard for consumer-level analog video recording on tape cassettes, introduced in 1976 by JVC. It was the dominant home video format throughout the tape media period of the 1980s and 1990s.
Ma ...
,
LaserDisc
LaserDisc (LD) is a home video format and the first commercial optical disc storage medium. It was developed by Philips, Pioneer Corporation, Pioneer, and the movie studio MCA Inc., MCA. The format was initially marketed in the United State ...
s,
CDs,
DVD
The DVD (common abbreviation for digital video disc or digital versatile disc) is a digital optical disc data storage format. It was invented and developed in 1995 and first released on November 1, 1996, in Japan. The medium can store any ki ...
s, and
Blu-ray disc
Blu-ray (Blu-ray Disc or BD) is a Digital media, digital optical disc data storage format designed to supersede the DVD format. It was invented and developed in 2005 and released worldwide on June 20, 2006, capable of storing several hours of ...
s, especially when compared with modern streaming media or content that has been downloaded from the Internet onto a hard drive or other storage device as files.
Types of physical media
Copper wire
Copper wire is currently the most commonly used type of physical media due to the abundance of copper in the world, as well as its ability to conduct electrical power.
Copper is also one of the cheaper metals which makes it more feasible to use.
Most copper wires used in data communications today have eight strands of copper, organized in unshielded
twisted pair
Twisted pair cabling is a type of communications cable in which two conductors of a single circuit are twisted together for the purposes of improving electromagnetic compatibility. Compared to a single conductor or an untwisted balanced ...
s, or UTP.
The wires are twisted around one another because it reduces electrical interference from outside sources. In addition to UTP, some wires use shielded twisted pairs (STP), which reduce electrical interference even further.
The way copper wires are twisted around one another also has an effect on data rates.
Category 3 cable
Category 3 cable, commonly known as or station wire, and less commonly known as VG or voice-grade (as, for example, in 100BaseVG), is an unshielded twisted pair (UTP) cable used in telephone wiring. It is part of a family of standards defin ...
(Cat3), has three to four twists per foot and can support speeds of 10
Mbit/s.
Category 5 cable
Category 5 cable (Cat 5) is a twisted pair cable for computer networks. Since 2001, the variant commonly in use is the Category 5e specification (Cat 5e). The cable standard provides performance of up to 100 MHz and is ...
(Cat5) is newer and has three to four twists per inch, which results in a maximum data rate of 100 Mbit/s.
In addition, there are category 5e (Cat5e) cables which can support speeds of up to 1,000 Mbit/s, and more recently, category 6 cables (Cat6), which support data rates of up to 10,000 Mbit/s (i.e., 10
Gbit/s).
On average, copper wire costs around $1 per foot.
Optical fiber
Optical fiber
An optical fiber, or optical fibre, is a flexible glass or plastic fiber that can transmit light from one end to the other. Such fibers find wide usage in fiber-optic communications, where they permit transmission over longer distances and at ...
is a thin and flexible piece of fiber made of glass or plastic. Unlike copper wire, optical fiber is typically used for long-distance data communications, being that it allows for data transmission over far distances and can produce high transmission speeds. Optical fiber also does not require signal repeaters, which ends up reducing maintenance costs, since signal repeaters are known to fail often.
There are two major types of optical fiber in use today. Multimode fiber is approximately 62.5
μm in diameter and utilizes
light-emitting diode
A light-emitting diode (LED) is a semiconductor device that emits light when current flows through it. Electrons in the semiconductor recombine with electron holes, releasing energy in the form of photons. The color of the light (corre ...
s to carry signals over a maximum distance of about 2 kilometers.
Single mode fiber is approximately 10 μm in diameter and is capable of carrying signals over tens of miles.
Like copper wire, optical fiber currently costs about $1 per foot.
Coaxial cables
Coaxial cables have two different layers surrounding a copper core. The inner most layer has an insulator. The next layer has a conducting shield. These are both covered by a plastic jacket. Coaxial cables are used for microwaves, televisions and computers.
This was the second transmission medium to be introduced (often called ''coax''), around the mid-1920s. In the center of a coaxial cable is a copper wire that acts as a conductor, where the information travels. The copper wire in coax is thicker than that in twisted-pair, and it is also unaffected by surrounding wires that contribute to
electromagnetic interference, so it can provide higher transmission rates than the twisted-pair. The center conductor is surrounded by plastic insulation, which helps filter out extraneous interference. This insulation is covered by a return path, which is usually braided-copper shielding or aluminum foil type covering. Outer jackets form a protective covering for coax; the number and type of outer jackets depend on the intended use of the cable (e.g., whether the cable is supposed to be strung in the air or underground, whether rodent protection is required). The two most popular types of coaxial cabling are used with
Ethernet
Ethernet ( ) is a family of wired computer networking technologies commonly used in local area networks (LAN), metropolitan area networks (MAN) and wide area networks (WAN). It was commercially introduced in 1980 and first standardized in 198 ...
networks.
Thinnet is used on Ethernet
10BASE2
10BASE2 (also known as cheapernet, thin Ethernet, thinnet, and thinwire) is a variant of Ethernet that uses thin coaxial cable terminated with BNC connectors to build a local area network. During the mid to late 1980s, this was the dominant ...
networks and is the thinner and more flexible of the two. Unlike a thicknet, it uses a
Bayonet Niell-Concelman (BNC) on each end to connect to computers. Thinnet is part of the RG-58 family of cable with a maximum cable length of 185 meters and transmission speeds of 10 Mbit/s.
Thicknet coaxial cabling is used with Ethernet
10BASE5
10BASE5 (also known as thick Ethernet or thicknet) was the first commercially available variant of Ethernet. The technology was standardized in 1982 as IEEE 802.3. 10BASE5 uses a thick and stiff coaxial cable up to in length. Up to 100 stat ...
networks, has a maximum cable length of 500 meters and transmission speeds of 10 Mbit/s. It's expensive and not commonly used, though it was originally used to directly connect computers. The computer is connected to the transceiver at the cable from the
attachment unit interface of its network card using a drop cable. Maximum thicknet nodes are 100 on a segment. One end of each cable is grounded.
Application
In the midst of the 1920s, coax was applied to telephone networks as inter-office
trunks. Rather than adding more copper cable bundles with 1500 or 1000 pairs of
copper wire and cable
Copper has been used in electrical wiring since the invention of the electromagnet and the telegraph in the 1820s. The invention of the telephone in 1876 created further demand for copper wire as an electrical conductor.
Copper is the electri ...
in them, it was possible to replace those big cables with much smaller coaxial cable.
The next major use of coax in telecommunications occurred in the 1950s, when it was deployed as
submarine cable to carry international traffic. It was then introduced into the data processing realm in the mid 1960s. Early computer architectures required coax as the media type from the terminal to the host.
Local area network
A local area network (LAN) is a computer network that interconnects computers within a limited area such as a residence, campus, or building, and has its network equipment and interconnects locally managed. LANs facilitate the distribution of da ...
s were predominantly based on coax from 1980 to about 1987.
Coax has also been used in
cable TV
Cable television is a system of delivering television broadcast programming, programming to consumers via radio frequency (RF) signals transmitted through coaxial cables, or in more recent systems, light pulses through fibre-optic cables. This ...
and the local loop, in the form of HFC architecture. HFC brings fiber as close as possible to the neighborhood. Fiber terminates at the neighborhood node, where coax fans out to provide home service.
Advantages
*
Broadband
In telecommunications, broadband or high speed is the wide-bandwidth (signal processing), bandwidth data transmission that exploits signals at a wide spread of frequencies or several different simultaneous frequencies, and is used in fast Inter ...
system-coax has sufficient frequency range to support multiple channels, allowing greater throughput.
* Greater channel capacity - each of the multiple channels offers substantial capacity depending on the service location (6 MHz wide in North America, 8 MHz wide in Europe).
* Greater bandwidth - compared to twisted pairs, it has greater bandwidth for each channel. This allows it to support a mixed range of services (voice, data, video, multimedia).
* Lower error rates - the inner conductor serves as a
Faraday shield that protects the network from electronic noise.
Disadvantages
* The
bus network
A bus network is a network topology in which Node (networking), nodes are directly connected to a common half-duplex link called a bus (computing), bus.
A Host (network), host on a bus network is called a ''station''. In a bus network, every ...
on which coax is deployed is susceptible to congestion, noise and security risks.
* Great noise - the return path has some noise problems, and the end equipment requires added intelligence to take care of error control.
*High installation costs
*Susceptible to damage from lightning strikes - if lightning is conducted by a
coaxial cable
Coaxial cable, or coax (pronounced ), is a type of electrical cable consisting of an inner Electrical conductor, conductor surrounded by a concentric conducting Electromagnetic shielding, shield, with the two separated by a dielectric (Insulat ...
, it could very easily damage the equipment at the end of it.
Debate on physical media
With technology constantly changing, there is a debate on whether ''physical media'' is still prudent and necessary to an increasingly wireless world.
Wireless and physical media may actually complement each other, and physical media will matter more, not less, in a society dominated by the wireless technology.
However, other opinions by people consider physical media a dead technology that will eventually disappear.
References
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Computer networking