Physical media

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Physical media refers to the physical materials that are used to store or transmit information in data communications. These physical media are generally physical objects made of materials such as copper or glass. They can be touched and felt, and have physical properties such as weight and color. [1] For a number of years, copper and glass were the only media used in computer networking.

Contents

The term physical media can also be used to describe data storage media like records, cassettes, VHS, LaserDiscs, CDs, DVDs, and Blu-rays, 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. [1] Copper is also one of the cheaper metals which makes it more feasible to use. [1]

Most copper wires used in data communications today have eight strands of copper, organized in unshielded twisted pairs, or UTP. [1] 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. [2] The way copper wires are twisted around one another also has an effect on data rates. Category 3 cable (Cat3), has three to four twists per foot and can support speeds of 10  Mbit/s. [1] Category 5 cable (Cat5) is newer and has three to four twists per inch, which results in a maximum data rate of 100 Mbit/s. [1] 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). [1]

On average, copper wire costs around $1 per foot. [1]

Optical fiber

Optical fiber 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. [1]

There are two major types of optical fiber in use today. Multimode fiber is approximately 62.5  μm in diameter and utilizes light-emitting diodes to carry signals over a maximum distance of about 2 kilometers. [1] Single mode fiber is approximately 10 μm in diameter and is capable of carrying signals over tens of miles. [1]

Like copper wire, optical fiber currently costs about $1 per foot. [1]

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 networks.

Thinnet is used on Ethernet 10BASE2 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 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. [2]

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 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 networks were predominantly based on coax from 1980 to about 1987.[ citation needed ]

Coax has also been used in cable TV 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. [3]

Advantages

  • Broadband 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 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, 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. [4] 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. [4] However, other opinions by people consider physical media a dead technology that will eventually disappear. [5]

Related Research Articles

<span class="mw-page-title-main">Ethernet</span> Computer networking technology

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 1983 as IEEE 802.3. Ethernet has since been refined to support higher bit rates, a greater number of nodes, and longer link distances, but retains much backward compatibility. Over time, Ethernet has largely replaced competing wired LAN technologies such as Token Ring, FDDI and ARCNET.

<span class="mw-page-title-main">Local area network</span> Computer network that connects devices over a limited area

A local area network (LAN) is a computer network that interconnects computers within a limited area such as a residence, school, laboratory, university campus or office building. By contrast, a wide area network (WAN) not only covers a larger geographic distance, but also generally involves leased telecommunication circuits.

<span class="mw-page-title-main">10BASE2</span> Once-dominant 10 Mbit/s Ethernet standard

10BASE2 is a variant of Ethernet that uses thin coaxial cable terminated with BNC connectors to build a local area network.

<span class="mw-page-title-main">Ethernet over twisted pair</span> Ethernet physical layers using twisted-pair cables

Ethernet over twisted-pair technologies use twisted-pair cables for the physical layer of an Ethernet computer network. They are a subset of all Ethernet physical layers.

<span class="mw-page-title-main">Fiber Distributed Data Interface</span> Standard for data transmission in a local area network

Fiber Distributed Data Interface (FDDI) is a standard for data transmission in a local area network. It uses optical fiber as its standard underlying physical medium, although it was also later specified to use copper cable, in which case it may be called CDDI, standardized as TP-PMD, also referred to as TP-DDI.

<span class="mw-page-title-main">Network topology</span> Arrangement of a communication network

Network topology is the arrangement of the elements of a communication network. Network topology can be used to define or describe the arrangement of various types of telecommunication networks, including command and control radio networks, industrial fieldbusses and computer networks.

<span class="mw-page-title-main">Transmission medium</span> Conduit for signal propagation

A transmission medium is a system or substance that can mediate the propagation of signals for the purposes of telecommunication. Signals are typically imposed on a wave of some kind suitable for the chosen medium. For example, data can modulate sound, and a transmission medium for sounds may be air, but solids and liquids may also act as the transmission medium. Vacuum or air constitutes a good transmission medium for electromagnetic waves such as light and radio waves. While a material substance is not required for electromagnetic waves to propagate, such waves are usually affected by the transmission media they pass through, for instance, by absorption or reflection or refraction at the interfaces between media. Technical devices can therefore be employed to transmit or guide waves. Thus, an optical fiber or a copper cable is used as transmission media.

<span class="mw-page-title-main">Fast Ethernet</span> Ethernet standards that carry data at the nominal rate of 100 Mbit/s

In computer networking, Fast Ethernet physical layers carry traffic at the nominal rate of 100 Mbit/s. The prior Ethernet speed was 10 Mbit/s. Of the Fast Ethernet physical layers, 100BASE-TX is by far the most common.

<span class="mw-page-title-main">Gigabit Ethernet</span> Standard for Ethernet networking at a data rate of 1 gigabit per second

In computer networking, Gigabit Ethernet is the term applied to transmitting Ethernet frames at a rate of a gigabit per second. The most popular variant, 1000BASE-T, is defined by the IEEE 802.3ab standard. It came into use in 1999, and has replaced Fast Ethernet in wired local networks due to its considerable speed improvement over Fast Ethernet, as well as its use of cables and equipment that are widely available, economical, and similar to previous standards. The first standard for faster 10 Gigabit Ethernet was approved in 2002.

<span class="mw-page-title-main">Twisted pair</span> Type of wiring used for communications

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 pair, a twisted pair reduces electromagnetic radiation from the pair and crosstalk between neighbouring pairs and improves rejection of external electromagnetic interference. It was invented by Alexander Graham Bell.

<span class="mw-page-title-main">HIPPI</span>

HIPPI, short for High Performance Parallel Interface, is a computer bus for the attachment of high speed storage devices to supercomputers, in a point-to-point link. It was popular in the late 1980s and into the mid-to-late 1990s, but has since been replaced by ever-faster standard interfaces like Fibre Channel and 10 Gigabit Ethernet.

<span class="mw-page-title-main">Medium Attachment Unit</span>

A Medium Attachment Unit (MAU) is a transceiver which converts signals on an Ethernet cable to and from Attachment Unit Interface (AUI) signals.

Fiber to the <i>x</i> Broadband network architecture term

Fiber to the x or fiber in the loop is a generic term for any broadband network architecture using optical fiber to provide all or part of the local loop used for last mile telecommunications. As fiber optic cables are able to carry much more data than copper cables, especially over long distances, copper telephone networks built in the 20th century are being replaced by fiber.

International standard ISO/IEC 11801Information technology — Generic cabling for customer premises specifies general-purpose telecommunication cabling systems that are suitable for a wide range of applications. It is published by ISO/IEC JTC 1/SC 25/WG 3 of the International Organization for Standardization (ISO) and the International Electrotechnical Commission (IEC). It covers both balanced copper cabling and optical fibre cabling.

<span class="mw-page-title-main">Computer network</span> Network that allows computers to share resources and communicate with each other

A computer network is a set of computers sharing resources located on or provided by network nodes. Computers use common communication protocols over digital interconnections to communicate with each other. These interconnections are made up of telecommunication network technologies based on physically wired, optical, and wireless radio-frequency methods that may be arranged in a variety of network topologies.

An Ethernet extender is any device used to extend an Ethernet or network segment beyond its inherent distance limitation which is approximately 100 metres (330 ft) for most common forms of twisted pair Ethernet. These devices employ a variety of transmission technologies and physical media.

<span class="mw-page-title-main">Ethernet physical layer</span> Electrical or optical properties between network devices

The physical-layer specifications of the Ethernet family of computer network standards are published by the Institute of Electrical and Electronics Engineers (IEEE), which defines the electrical or optical properties and the transfer speed of the physical connection between a device and the network or between network devices. It is complemented by the MAC layer and the logical link layer. An implementation of a specific physical layer is commonly referred to as PHY.

Ethernet in the first mile (EFM) refers to using one of the Ethernet family of computer network technologies between a telecommunications company and a customer's premises. From the customer's point of view, it is their first mile, although from the access network's point of view it is known as the last mile.

Networking cable is a piece of networking hardware used to connect one network device to other network devices or to connect two or more computers to share devices such as printers or scanners. Different types of network cables, such as coaxial cable, optical fiber cable, and twisted pair cables, are used depending on the network's topology, protocol, and size. The devices can be separated by a few meters or nearly unlimited distances.

Classic Ethernet is a family of 10 Mbit/s Ethernet standards, which is the first generation of Ethernet standards. In 10BASE-X, the 10 represents its maximum throughput of 10 Mbit/s, BASE indicates its use of baseband transmission, and X indicates the type of medium used. Classic Ethernet includes coax, twisted pair and optical variants. The first Ethernet standard was published in 1983 and classic Ethernet operating at 10 Mbit/s was the dominant form of Ethernet until the first standard for Fast Ethernet was approved in 1995.

References

  1. 1 2 3 4 5 6 7 8 9 10 11 12 Agrawal, Manish (2010). Business Data Communications. John Wiley & Sons. pp. 36–44. ISBN   9780470483367.
  2. 1 2 "Physical Media" . Retrieved 5 December 2012.
  3. Lilian, Goleniewski (2007). Telecommunication Essentials. Addison Wesley Professional. p. 928. ISBN   978-0-13-290777-4.
  4. 1 2 Hon, Adrian. "Why physical media still matters". Telegraph Media Group Limited. Archived from the original on 2011-06-03. Retrieved 2017-11-30.
  5. Malik, Om. "Physical Media Is Dead, Long Live the App". GIGAOM. Retrieved 2017-11-30.