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History Of Data Communication Essay Free

Since prehistoric times, significant changes in communication technologies (media and appropriate inscription tools) have evolved in tandem with shifts in political and economic systems, and by extension, systems of power. Communication can range from very subtle processes of exchange, to full conversations and mass communication. Human communication was revolutionized with the origin of speech approximately 500,000 years ago. Symbols were developed about 30,000 years ago. The imperfection of speech, which nonetheless allowed easier dissemination of ideas and stimulated inventions, eventually resulted in the creation of new forms of communications, improving both the range at which people could communicate and the longevity of the information. All of those inventions were based on the key concept of the symbol.

The oldest known symbols created for the purpose of communication were cave paintings, a form of rock art, dating to the Upper Paleolithic age. The oldest known cave painting is located within Chauvet Cave, dated to around 30,000 BC.[1] These paintings contained increasing amounts of information: people may have created the first calendar as far back as 15,000 years ago.[2] The connection between drawing and writing is further shown by linguistics: in Ancient Egypt and Ancient Greece the concepts and words of drawing and writing were one and the same (Egyptian: 's-sh', Greek: 'graphein').[3]

Petroglyphs[edit]

Further information: Petroglyphs

The next advancement in the history of communications came with the production of petroglyphs, carvings into a rock surface. It took about 20,000 years for homo sapiens to move from the first cave paintings to the first petroglyphs, which are dated to around 10,000BC.[4]

It is possible that humans of that time used some other forms of communication, often for mnemonic purposes - specially arranged stones, symbols carved in wood or earth, quipu-like ropes, tattoos, but little other than the most durable carved stones has survived to modern times and we can only speculate about their existence based on our observation of still existing 'hunter-gatherer' cultures such as those of Africa or Oceania.[5] ÷

Pictograms[edit]

Further information: Pictograms

A pictogram (pictograph) is a symbol representing a concept, object, activity, place or event by illustration. Pictography is a form of proto-writing whereby ideas are transmitted through drawing. Pictographs were the next step in the evolution of communication: the most important difference between petroglyphs and pictograms is that petroglyphs are simply showing an event, but pictograms are telling a story about the event, thus they can for example be ordered chronologically.

Pictograms were used by various ancient cultures all over the world since around 9000 BC, when tokens marked with simple pictures began to be used to label basic farm produce, and become increasingly popular around 6000-5000 BC.

They were the basis of cuneiform[6] and hieroglyphs, and began to develop into logographicwriting systems around 5000 BC.

Ideograms[edit]

Further information: Ideograms

Pictograms, in turn, evolved into ideograms, graphical symbols that represent an idea. Their ancestors, the pictograms, could represent only something resembling their form: therefore a pictogram of a circle could represent a sun, but not concepts like 'heat', 'light', 'day' or 'Great God of the Sun'. Ideograms, on the other hand, could convey more abstract concepts, so that for example an ideogram of two sticks can mean not only 'legs' but also a verb 'to walk'.

Because some ideas are universal, many different cultures developed similar ideograms. For example, an eye with a tear means 'sadness' in Native American ideograms in California, as it does for the Aztecs, the early Chinese and the Egyptians.[citation needed]

Ideograms were precursors of logographic writing systems such as Egyptian hieroglyphs and Chinese characters.[citation needed]

Examples of ideographical proto-writing systems, thought not to contain language-specific information, include the Vinca script (see also Tărtăria tablets) and the early Indus script.[citation needed] In both cases there are claims of decipherment of linguistic content, without wide acceptance.[citation needed]

Writing[edit]

Further information: History of writing

The oldest-known forms of writing were primarily logographic in nature, based on pictographic and ideographic elements. Most writing systems can be broadly divided into three categories: logographic, syllabic and alphabetic (or segmental); however, all three may be found in any given writing system in varying proportions, often making it difficult to categorise a system uniquely.

The invention of the first writing systems is roughly contemporary in with the beginning of the Bronze Age in the late Neolithic of the late 4000 BC. The first writing system is generally believed to have been invented in pre-historic Sumer and developed by the late 3000's BC into cuneiform. Egyptian hieroglyphs, and the undeciphered Proto-Elamite writing system and Indus Valley script also date to this era, though a few scholars have questioned the Indus Valley script's status as a writing system.

The original Sumerian writing system was derived from a system of claytokens used to represent commodities. By the end of the 4th millennium BC, this had evolved into a method of keeping accounts, using a round-shaped stylus impressed into soft clay at different angles for recording numbers. This was gradually augmented with pictographic writing using a sharp stylus to indicate what was being counted. Round-stylus and sharp-stylus writing was gradually replaced about 2700-2000 BC by writing using a wedge-shaped stylus (hence the term cuneiform), at first only for logograms, but developed to include phonetic elements by the 2800 BC. About 2600 BC cuneiform began to represent syllables of spoken Sumerian language.

Finally, cuneiform writing became a general purpose writing system for logograms, syllables, and numbers. By the 26th century BC, this script had been adapted to another Mesopotamian language, Akkadian, and from there to others such as Hurrian, and Hittite. Scripts similar in appearance to this writing system include those for Ugaritic and Old Persian.

The Chinese script may have originated independently of the Middle Eastern scripts, around the 16th century BC (early Shang Dynasty), out of a late neolithic Chinese system of proto-writing dating back to c. 6000 BC. The pre-Columbian writing systems of the Americas, including Olmec and Mayan, are also generally believed to have had independent origins.

Alphabet[edit]

Further information: history of alphabet

The first pure alphabets (properly, "abjads", mapping single symbols to single phonemes, but not necessarily each phoneme to a symbol) emerged around 2000 BC in Ancient Egypt, but by then alphabetic principles had already been incorporated into Egyptian hieroglyphs for a millennium (see Middle Bronze Age alphabets).

By 2700 BC Egyptian writing had a set of some 22 hieroglyphs to represent syllables that begin with a single consonant of their language, plus a vowel (or no vowel) to be supplied by the native speaker. These glyphs were used as pronunciation guides for logograms, to write grammatical inflections, and, later, to transcribe loan words and foreign names.

However, although seemingly alphabetic in nature, the original Egyptian uniliterals were not a system and were never used by themselves to encode Egyptian speech. In the Middle Bronze Age an apparently "alphabetic" system is thought by some to have been developed in central Egypt around 1700 BC for or by Semitic workers, but we cannot read these early writings and their exact nature remains open to interpretation.

Over the next five centuries this Semitic "alphabet" (really a syllabary like Phoenician writing) seems to have spread north. All subsequent alphabets around the world[citation needed] with the sole exception of Korean Hangul have either descended from it, or been inspired by one of its descendants.

History of telecommunication[edit]

Further information: History of telecommunication

The history of telecommunication - the transmission of signals over a distance for the purpose of communication - began thousands of years ago with the use of smoke signals and drums in Africa, America and parts of Asia. In the 1790s the first fixed semaphore systems emerged in Europe however it was not until the 1830s that electrical [telecommunication] systems started to appear.

Timeline[edit]

Main article: Timeline of communication technology

See also[edit]

References[edit]

Further reading[edit]

  • Asante, Molefi Kete, Yoshitaka Miike, and Jing Yin, eds. The global intercultural communication reader (Routledge, 2013)
  • Berger, Arthur Asa. Media and communication research methods: An introduction to qualitative and quantitative approaches (SAGE 2013)
  • Burke, Peter. A Social History of Knowledge: From Gutenberg to Diderot (2000)
  • Burke, Peter. A Social History of Knowledge II: From the Encyclopaedia to Wikipedia (2012)
  • de Mooij, Marieke. "Theories of Mass Communication and Media Effects Across Cultures." in Human and Mediated Communication around the World (Springer 2014) pp 355–393.
  • Esser, Frank, and Thomas Hanitzsch, eds. The handbook of comparative communication research (Routledge, 2012)
  • Gliek, James (2011). The Information: A History, a Theory, a Flood. ISBN 978-0-375-42372-7. 
  • Jensen, Klaus Bruhn, ed. A handbook of media and communication research: qualitative and quantitative methodologies (Routledge, 2013)
  • Paxson, Peyton. Mass Communications and Media Studies: An Introduction (Bloomsbury, 2010)
  • Poe, Marshall T. A History of Communications: Media and Society From the Evolution of Speech to the Internet (Cambridge University Press; 2011) 352 pages; Documents how successive forms of communication are embraced and, in turn, foment change in social institutions.
  • Schramm, Wilbur. Mass Communications (1963)
  • Schramm, Wilbur, ed. Mass Communications: A Reader (1960)
  • Simonson, Peter. Refiguring Mass Communication: A History (2010)
  1. ^Paul Martin Lester, Visual Communication with Infotrac: Images with Messages, Thomson Wadsworth, 2005, ISBN 0-534-63720-5, Google Print: p.48
  2. ^according to a claim by Michael Rappenglueck, of the University of Munich (2000) [1]
  3. ^David Diringer, The Book Before Printing: Ancient, Medieval and Oriental, Courier Dover Publications, 1982, ISBN 0-486-24243-9, Google Print: p.27
  4. ^Cite error: The named reference was invoked but never defined (see the help page).
  5. ^David Diringer, History of the Alphabet, 1977; ISBN 0-905418-12-3.
  6. ^"Linguistics 201: The Invention of Writing". Pandora.cii.wwu.edu. Retrieved 2012-10-02. 

"Datacom" redirects here. For other uses, see Datacom (disambiguation).

A computer network, or data network, is a digitaltelecommunications network which allows nodes to share resources. In computer networks, computing devicesexchange data with each other using connections between nodes (data links.) These data links are established over cable media such as wires or optic cables, or wireless media such as WiFi.

Network computer devices that originate, route and terminate the data are called network nodes.[1] Nodes can include hosts such as personal computers, phones, servers as well as networking hardware. Two such devices can be said to be networked together when one device is able to exchange information with the other device, whether or not they have a direct connection to each other. In most cases, application-specific communications protocols are layered (i.e. carried as payload) over other more general communications protocols. This formidable collection of information technology requires skilled network management to keep it all running reliably.

Computer networks support an enormous number of applications and services such as access to the World Wide Web, digital video, digital audio, shared use of application and storage servers, printers, and fax machines, and use of email and instant messaging applications as well as many others. Computer networks differ in the transmission medium used to carry their signals, communications protocols to organize network traffic, the network's size, topology, traffic control mechanism and organizational intent. The best-known computer network is the Internet.

History[edit]

See also: History of the Internet

The chronology of significant computer-network developments includes:

  • In the late 1950s, early networks of computers included the U.S. military radar system Semi-Automatic Ground Environment (SAGE).
  • In 1959, Anatolii Ivanovich Kitov proposed to the Central Committee of the Communist Party of the Soviet Union a detailed plan for the re-organisation of the control of the Soviet armed forces and of the Soviet economy on the basis of a network of computing centres, the OGAS.[2]
  • In 1960, the commercial airline reservation system semi-automatic business research environment (SABRE) went online with two connected mainframes.
  • In 1963, J. C. R. Licklider sent a memorandum to office colleagues discussing the concept of the "Intergalactic Computer Network", a computer network intended to allow general communications among computer users.
  • In 1964, researchers at Dartmouth College developed the Dartmouth Time Sharing System for distributed users of large computer systems. The same year, at Massachusetts Institute of Technology, a research group supported by General Electric and Bell Labs used a computer to route and manage telephone connections.
  • Throughout the 1960s, Paul Baran, and Donald Davies independently developed the concept of packet switching to transfer information between computers over a network. Davies pioneered the implementation of the concept with the NPL network, a local area network at the National Physical Laboratory (United Kingdom) using a line speed of 768 kbit/s.[3][4][5]
  • In 1965, Western Electric introduced the first widely used telephone switch that implemented true computer control.
  • In 1966, Thomas Marill and Lawrence G. Roberts published a paper on an experimental wide area network (WAN) for computer time sharing.[6]
  • In 1969, the first four nodes of the ARPANET were connected using 50 kbit/s circuits between the University of California at Los Angeles, the Stanford Research Institute, the University of California at Santa Barbara, and the University of Utah.[7]Leonard Kleinrock carried out theoretical work to model the performance of packet-switched networks, which underpinned the development of the ARPANET.[8][9] His theoretical work on hierarchical routing in the late 1970s with student Farouk Kamoun remains critical to the operation of the Internet today.
  • In 1972, commercial services using X.25 were deployed, and later used as an underlying infrastructure for expanding TCP/IP networks.
  • In 1973, the French CYCLADES network was the first to make the hosts responsible for the reliable delivery of data, rather than this being a centralized service of the network itself.[10]
  • In 1973, Robert Metcalfe wrote a formal memo at Xerox PARC describing Ethernet, a networking system that was based on the Aloha network, developed in the 1960s by Norman Abramson and colleagues at the University of Hawaii. In July 1976, Robert Metcalfe and David Boggs published their paper "Ethernet: Distributed Packet Switching for Local Computer Networks"[11] and collaborated on several patents received in 1977 and 1978. In 1979, Robert Metcalfe pursued making Ethernet an open standard.[12]
  • In 1976, John Murphy of Datapoint Corporation created ARCNET, a token-passing network first used to share storage devices.
  • In 1995, the transmission speed capacity for Ethernet increased from 10 Mbit/s to 100 Mbit/s. By 1998, Ethernet supported transmission speeds of a Gigabit. Subsequently, higher speeds of up to 100 Gbit/s were added (as of 2016[update]). The ability of Ethernet to scale easily (such as quickly adapting to support new fiber optic cable speeds) is a contributing factor to its continued use.[12]

Properties[edit]

Computer networking may be considered a branch of electrical engineering, electronics engineering, telecommunications, computer science, information technology or computer engineering, since it relies upon the theoretical and practical application of the related disciplines.

A computer network facilitates interpersonal communications allowing users to communicate efficiently and easily via various means: email, instant messaging, online chat, telephone, video telephone calls, and video conferencing. A network allows sharing of network and computing resources. Users may access and use resources provided by devices on the network, such as printing a document on a shared network printer or use of a shared storage device. A network allows sharing of files, data, and other types of information giving authorized users the ability to access information stored on other computers on the network. Distributed computing uses computing resources across a network to accomplish tasks.

A computer network may be used by security hackers to deploy computer viruses or computer worms on devices connected to the network, or to prevent these devices from accessing the network via a denial-of-service attack.

Network packet[edit]

Main article: Network packet

Computer communication links that do not support packets, such as traditional point-to-point telecommunication links, simply transmit data as a bit stream. However, most information in computer networks is carried in packets. A network packet is a formatted unit of data (a list of bits or bytes, usually a few tens of bytes to a few kilobytes long) carried by a packet-switched network. Packets are sent through the network to their destination. Once the packets arrive they are reassembled into their original message.

Packets consist of two kinds of data: control information, and user data (payload). The control information provides data the network needs to deliver the user data, for example: source and destination network addresses, error detection codes, and sequencing information. Typically, control information is found in packet headers and trailers, with payload data in between.

With packets, the bandwidth of the transmission medium can be better shared among users than if the network were circuit switched. When one user is not sending packets, the link can be filled with packets from other users, and so the cost can be shared, with relatively little interference, provided the link isn't overused. Often the route a packet needs to take through a network is not immediately available. In that case the packet is queued and waits until a link is free.

Network topology[edit]

Main article: Network topology

The physical layout of a network is usually less important than the topology that connects network nodes. Most diagrams that describe a physical network are therefore topological, rather than geographic. The symbols on these diagrams usually denote network links and network nodes.

Network links[edit]

Further information: data transmission

The transmission media (often referred to in the literature as the physical media) used to link devices to form a computer network include electrical cable, optical fiber, and radio waves. In the OSI model, these are defined at layers 1 and 2 — the physical layer and the data link layer.

A widely adopted family of transmission media used in local area network (LAN) technology is collectively known as Ethernet. The media and protocol standards that enable communication between networked devices over Ethernet are defined by IEEE 802.3. Ethernet transmits data over both copper and fiber cables. Wireless LAN standards use radio waves, others use infrared signals as a transmission medium. Power line communication uses a building's power cabling to transmit data.

Wired technologies[edit]

The orders of the following wired technologies are, roughly, from slowest to fastest transmission speed.

  • Coaxial cable is widely used for cable television systems, office buildings, and other work-sites for local area networks. The cables consist of copper or aluminum wire surrounded by an insulating layer (typically a flexible material with a high dielectric constant), which itself is surrounded by a conductive layer. The insulation helps minimize interference and distortion. Transmission speed ranges from 200 million bits per second to more than 500 million bits per second.
  • ITU-TG.hn technology uses existing home wiring (coaxial cable, phone lines and power lines) to create a high-speed (up to 1 Gigabit/s) local area network
  • Twisted pair wire is the most widely used medium for all telecommunication. Twisted-pair cabling consist of copper wires that are twisted into pairs. Ordinary telephone wires consist of two insulated copper wires twisted into pairs. Computer network cabling (wired Ethernet as defined by IEEE 802.3) consists of 4 pairs of copper cabling that can be utilized for both voice and data transmission. The use of two wires twisted together helps to reduce crosstalk and electromagnetic induction. The transmission speed ranges from 2 million bits per second to 10 billion bits per second. Twisted pair cabling comes in two forms: unshielded twisted pair (UTP) and shielded twisted-pair (STP). Each form comes in several category ratings, designed for use in various scenarios.
  • An optical fiber is a glass fiber. It carries pulses of light that represent data. Some advantages of optical fibers over metal wires are very low transmission loss and immunity from electrical interference. Optical fibers can simultaneously carry multiple wavelengths of light, which greatly increases the rate that data can be sent, and helps enable data rates of up to trillions of bits per second. Optic fibers can be used for long runs of cable carrying very high data rates, and are used for undersea cables to interconnect continents.

Price is a main factor distinguishing wired- and wireless-technology options in a business. Wireless options command a price premium that can make purchasing wired computers, printers and other devices a financial benefit. Before making the decision to purchase hard-wired technology products, a review of the restrictions and limitations of the selections is necessary. Business and employee needs may override any cost considerations.[13]

Wireless technologies[edit]

Main article: Wireless network

  • Terrestrial microwave – Terrestrial microwave communication uses Earth-based transmitters and receivers resembling satellite dishes. Terrestrial microwaves are in the low gigahertz range, which limits all communications to line-of-sight. Relay stations are spaced approximately 48 km (30 mi) apart.
  • Communications satellites – Satellites communicate via microwave radio waves, which are not deflected by the Earth's atmosphere. The satellites are stationed in space, typically in geosynchronous orbit 35,400 km (22,000 mi) above the equator. These Earth-orbiting systems are capable of receiving and relaying voice, data, and TV signals.
  • Cellular and PCS systems use several radio communications technologies. The systems divide the region covered into multiple geographic areas. Each area has a low-power transmitter or radio relay antenna device to relay calls from one area to the next area.
  • Radio and spread spectrum technologies – Wireless local area networks use a high-frequency radio technology similar to digital cellular and a low-frequency radio technology. Wireless LANs use spread spectrum technology to enable communication between multiple devices in a limited area. IEEE 802.11 defines a common flavor of open-standards wireless radio-wave technology known as Wifi.
  • Free-space optical communication uses visible or invisible light for communications. In most cases, line-of-sight propagation is used, which limits the physical positioning of communicating devices.

Exotic technologies[edit]

There have been various attempts at transporting data over exotic media:

Both cases have a large round-trip delay time, which gives slow two-way communication, but doesn't prevent sending large amounts of information.

Network nodes[edit]

Main article: Node (networking)

Apart from any physical transmission media there may be, networks comprise additional basic system building blocks, such as network interface controllers (NICs), repeaters, hubs, bridges, switches, routers, modems, and firewalls. Any particular piece of equipment will frequently contain multiple building blocks and perform multiple functions.

Network interfaces[edit]

A network interface controller (NIC) is computer hardware that provides a computer with the ability to access the transmission media, and has the ability to process low-level network information. For example, the NIC may have a connector for accepting a cable, or an aerial for wireless transmission and reception, and the associated circuitry.

The NIC responds to traffic addressed to a network address for either the NIC or the computer as a whole.

In Ethernet networks, each network interface controller has a unique Media Access Control (MAC) address—usually stored in the controller's permanent memory. To avoid address conflicts between network devices, the Institute of Electrical and Electronics Engineers (IEEE) maintains and administers MAC address uniqueness. The size of an Ethernet MAC address is six octets. The three most significant octets are reserved to identify NIC manufacturers. These manufacturers, using only their assigned prefixes, uniquely assign the three least-significant octets of every Ethernet interface they produce.

Repeaters and hubs[edit]

A repeater is an electronic device that receives a network signal, cleans it of unnecessary noise and regenerates it. The signal is retransmitted at a higher power level, or to the other side of an obstruction, so that the signal can cover longer distances without degradation. In most twisted pair Ethernet configurations, repeaters are required for cable that runs longer than 100 meters. With fiber optics, repeaters can be tens or even hundreds of kilometers apart.

A repeater with multiple ports is known as an Ethernet hub. Repeaters work on the physical layer of the OSI model. Repeaters require a small amount of time to regenerate the signal. This can cause a propagation delay that affects network performance and may affect proper function. As a result, many network architectures limit the number of repeaters that can be used in a row, e.g., the Ethernet 5-4-3 rule.

Hubs and repeaters in LANs have been mostly obsoleted by modern switches.

Bridges[edit]

A network bridge connects and filters traffic between two network segments at the data link layer (layer 2) of the OSI model to form a single network. This breaks the network's collision domain but maintains a unified broadcast domain. Network segmentation breaks down a large, congested network into an aggregation of smaller, more efficient networks.

Bridges come in three basic types:

  • Local bridges: Directly connect LANs
  • Remote bridges: Can be used to create a wide area network (WAN) link between LANs. Remote bridges, where the connecting link is slower than the end networks, largely have been replaced with routers.
  • Wireless bridges: Can be used to join LANs or connect remote devices to LANs.

Switches[edit]

A network switch is a device that forwards and filters OSI layer 2datagrams (frames) between ports based on the destination MAC address in each frame.[16] A switch is distinct from a hub in that it only forwards the frames to the physical ports involved in the communication rather than all ports connected. It can be thought of as a multi-port bridge.[17] It learns to associate physical ports to MAC addresses by examining the source addresses of received frames. If an unknown destination is targeted, the switch broadcasts to all ports but the source. Switches normally have numerous ports, facilitating a star topology for devices, and cascading additional switches.

Multi-layer switches are capable of routing based on layer 3 addressing or additional logical levels. The term switch is often used loosely to include devices such as routers and bridges, as well as devices that may distribute traffic based on load or based on application content (e.g., a Web URL identifier).

Routers[edit]

A router is an internetworking device that forwards packets between networks by processing the routing information included in the packet or datagram (Internet protocol information from layer 3). The routing information is often processed in conjunction with the routing table (or forwarding table). A router uses its routing table to determine where to forward packets. A destination in a routing table can include a "null" interface, also known as the "black hole" interface because data can go into it, however, no further processing is done for said data, i.e. the packets are dropped.

Modems[edit]

Modems (MOdulator-DEModulator) are used to connect network nodes via wire not originally designed for digital network traffic, or for wireless. To do this one or more carrier signals are modulated by the digital signal to produce an analog signal that can be tailored to give the required properties for transmission. Modems are commonly used for telephone lines, using a Digital Subscriber Line technology.

Firewalls[edit]

A firewall is a network device for controlling network security and access rules. Firewalls are typically configured to reject access requests from unrecognized sources while allowing actions from recognized ones. The vital role firewalls play in network security grows in parallel with the constant increase in cyber attacks.

Network structure[edit]

Network topology is the layout or organizational hierarchy of interconnected nodes of a computer network. Different network topologies can affect throughput, but reliability is often more critical. With many technologies, such as bus networks, a single failure can cause the network to fail entirely. In general the more interconnections there are, the more robust the network is; but the more expensive it is to install.

Common layouts[edit]

Common layouts are:

  • A bus network: all nodes are connected to a common medium along this medium. This was the layout used in the original Ethernet, called 10BASE5 and 10BASE2.
  • A star network: all nodes are connected to a special central node. This is the typical layout found in a Wireless LAN, where each wireless client connects to the central Wireless access point.
  • A ring network: each node is connected to its left and right neighbour node, such that all nodes are connected and that each node can reach each other node by traversing nodes left- or rightwards. The Fiber Distributed Data Interface (FDDI) made use of such a topology.
  • A mesh network: each node is connected to an arbitrary number of neighbours in such a way that there is at least one traversal from any node to any other.
  • A fully connected network: each node is connected to every other node in the network.
  • A tree network: nodes are arranged hierarchically.

Note that the physical layout of the nodes in a network may not necessarily reflect the network topology. As an example, with FDDI, the network topology is a ring (actually two counter-rotating rings), but the physical topology is often a star, because all neighboring connections can be routed via a central physical location.

Overlay network[edit]

An overlay network is a virtual computer network that is built on top of another network. Nodes in the overlay network are connected by virtual or logical links. Each link corresponds to a path, perhaps through many physical links, in the underlying network. The topology of the overlay network may (and often does) differ from that of the underlying one. For example, many peer-to-peer networks are overlay networks. They are organized as nodes of a virtual system of links that run on top of the Internet.[18]

Overlay networks have been around since the invention of networking when computer systems were connected over telephone lines using modems, before any data network existed.

The most striking example of an overlay network is the Internet itself. The Internet itself was initially built as an overlay on the telephone network.[18] Even today, each Internet node can communicate with virtually any other through an underlying mesh of sub-networks of wildly different topologies and technologies. Address resolution and routing are the means that allow mapping of a fully connected IP overlay network to its underlying network.

Another example of an overlay network is a distributed hash table, which maps keys to nodes in the network. In this case, the underlying network is an IP network, and the overlay network is a table (actually a map) indexed by keys.

Overlay networks have also been proposed as a way to improve Internet routing, such as through quality of service guarantees to achieve higher-quality streaming media. Previous proposals such as IntServ, DiffServ, and IP Multicast have not seen wide acceptance largely because they require modification of all routers in the network.[citation needed] On the other hand, an overlay network can be incrementally deployed on end-hosts running the overlay protocol software, without cooperation from Internet service providers. The overlay network has no control over how packets are routed in the underlying network between two overlay nodes, but it can control, for example, the sequence of overlay nodes that a message traverses before it reaches its destination.

For example, Akamai Technologies manages an overlay network that provides reliable, efficient content delivery (a kind of multicast). Academic research includes end system multicast,[19] resilient routing and quality of service studies, among others.

Communication protocols[edit]

A communication protocol is a set of rules for exchanging information over a network. In a protocol stack (also see the OSI model), each protocol leverages the services of the protocol layer below it, until the lowest layer controls the hardware which sends information across the media. The use of protocol layering is today ubiquitous across the field of computer networking. An important example of a protocol stack is HTTP (the World Wide Web protocol) running over TCP over IP (the Internet protocols) over IEEE 802.11 (the Wi-Fi protocol). This stack is used between the wireless router and the home user's personal computer when the user is surfing the web.

Communication protocols have various characteristics. They may be connection-oriented or connectionless, they may use circuit mode or packet switching, and they may use hierarchical addressing or flat addressing.

There are many communication protocols, a few of which are described below.

IEEE 802[edit]

IEEE 802 is a family of IEEE standards dealing with local area networks and metropolitan area networks. The complete IEEE 802 protocol suite provides a diverse set of networking capabilities. The protocols have a flat addressing scheme. They operate mostly at levels 1 and 2 of the OSI model.

For example, MACbridging (IEEE 802.1D) deals with the routing of Ethernet packets using a Spanning Tree Protocol. IEEE 802.1Q describes VLANs, and IEEE 802.1X defines a port-based Network Access Control protocol, which forms the basis for the authentication mechanisms used in VLANs (but it is also found in WLANs) – it is what the home user sees when the user has to enter a "wireless access key".

Ethernet[edit]

Ethernet, sometimes simply called LAN, is a family of protocols used in wired LANs, described by a set of standards together called IEEE 802.3 published by the Institute of Electrical and Electronics Engineers.

Wireless LAN[edit]

Wireless LAN, also widely known as WLAN or WiFi, is probably the most well-known member of the IEEE 802 protocol family for home users today. It is standardized by IEEE 802.11 and shares many properties with wired Ethernet.

Internet Protocol Suite[edit]

The Internet Protocol Suite, also called TCP/IP, is the foundation of all modern networking. It offers connection-less as well as connection-oriented services over an inherently unreliable network traversed by data-gram transmission at the Internet protocol (IP) level. At its core, the protocol suite defines the addressing, identification, and routing specifications for Internet Protocol Version 4 (IPv4) and for IPv6, the next generation of the protocol with a much enlarged addressing capability.

SONET/SDH[edit]

Synchronous optical networking (SONET) and Synchronous Digital Hierarchy (SDH) are standardized multiplexing protocols that transfer multiple digital bit streams over optical fiber using lasers. They were originally designed to transport circuit mode communications from a variety of different sources, primarily to support real-time, uncompressed, circuit-switched voice encoded in PCM (Pulse-Code Modulation) format. However, due to its protocol neutrality and transport-oriented features, SONET/SDH also was the obvious choice for transporting Asynchronous Transfer Mode (ATM) frames.

Asynchronous Transfer Mode[edit]

Asynchronous Transfer Mode (ATM) is a switching technique for telecommunication networks. It uses asynchronous time-division multiplexing and encodes data into small, fixed-sized cells. This differs from other protocols such as the Internet Protocol Suite or Ethernet that use variable sized packets or frames. ATM has similarity with both circuit and packet switched networking. This makes it a good choice for a network that must handle both traditional high-throughput data traffic, and real-time, low-latency content such as voice and video. ATM uses a connection-oriented model in which a virtual circuit must be established between two endpoints before the actual data exchange begins.

While the role of ATM is diminishing in favor of next-generation networks, it still plays a role in the last mile, which is the connection between an Internet service provider and the home user.[20]

Cellular standards[edit]

There are a number of different digital cellular standards, including: Global System for Mobile Communications (GSM), General Packet Radio Service (GPRS), cdmaOne, CDMA2000, Evolution-Data Optimized (EV-DO), Enhanced Data Rates for GSM Evolution (EDGE), Universal Mobile Telecommunications System (UMTS), Digital Enhanced Cordless Telecommunications (DECT), Digital AMPS (IS-136/TDMA), and Integrated Digital Enhanced Network (iDEN).[21]

Geographic scale[edit]

A network can be characterized by its physical capacity or its organizational purpose. Use of the network, including user authorization and access rights, differ accordingly.

Nanoscale network

A nanoscale communication network has key components implemented at the nanoscale including message carriers and leverages physical principles that differ from macroscale communication mechanisms. Nanoscale communication extends communication to very small sensors and actuators such as those found in biological systems and also tends to operate in environments that would be too harsh for classical communication.[22]

Personal area network

A personal area network (PAN) is a computer network used for communication among computer and different information technological devices close to one person. Some examples of devices that are used in a PAN are personal computers, printers, fax machines, telephones, PDAs, scanners, and even video game consoles. A PAN may include wired and wireless devices. The reach of a PAN typically extends to 10 meters.[23] A wired PAN is usually constructed with USB and FireWire connections while technologies such as Bluetooth and infrared communication typically form a wireless PAN.

Local area network

A local area network (LAN) is a network that connects computers and devices in a limited geographical area such as a home, school, office building, or closely positioned group of buildings. Each computer or device on the network is a node. Wired LANs are most likely based on Ethernet technology. Newer standards such as ITU-TG.hn also provide a way to create a wired LAN using existing wiring, such as coaxial cables, telephone lines, and power lines.[24]

The defining characteristics of a LAN, in contrast to a wide area network (WAN), include higher data transfer rates, limited geographic range, and lack of reliance on leased lines to provide connectivity. Current Ethernet or other IEEE 802.3 LAN technologies operate at data transfer rates up to 100 Gbit/s, standardized by IEEE in 2010.[25] Currently, 400 Gbit/s Ethernet is being developed.

A LAN can be connected to a WAN using a router.

Home area network

A home area network (HAN) is a residential LAN used for communication between digital devices typically deployed in the home, usually a small number of personal computers and accessories, such as printers and mobile computing devices. An important function is the sharing of Internet access, often a broadband service through a cable TV or digital subscriber line (DSL) provider.

Storage area network

A storage area network (SAN) is a dedicated network that provides access to consolidated, block level data storage. SANs are primarily used to make storage devices, such as disk arrays, tape libraries, and optical jukeboxes, accessible to servers so that the devices appear like locally attached devices to the operating system. A SAN typically has its own network of storage devices that are generally not accessible through the local area network by other devices. The cost and complexity of SANs dropped in the early 2000s to levels allowing wider adoption across both enterprise and small to medium-sized business environments.

Campus area network

A campus area network (CAN) is made up of an interconnection of LANs within a limited geographical area. The networking equipment (switches, routers) and transmission media (optical fiber, copper plant, Cat5 cabling, etc.) are almost entirely owned by the campus tenant / owner (an enterprise, university, government, etc.).

For example, a university campus network is likely to link a variety of campus buildings to connect academic colleges or departments, the library, and student residence halls.

Backbone network

A backbone network is part of a computer network infrastructure that provides a path for the exchange of information between different LANs or sub-networks. A backbone can tie together diverse networks within the same building, across different buildings, or over a wide area.

For example, a large company might implement a backbone network to connect departments that are located around the world. The equipment that ties together the departmental networks constitutes the network backbone. When designing a network backbone, network performance and network congestion are critical factors to take into account. Normally, the backbone network's capacity is greater than that of the individual networks connected to it.

Another example of a backbone network is the Internet backbone, which is the set of wide area networks (WANs) and core routers that tie together all networks connected to the Internet.

Metropolitan area network

A Metropolitan area network (MAN) is a large computer network that usually spans a city or a large campus.

Wide area network

A wide area network

2007 map showing submarine optical fiber telecommunication cables around the world.
Computers are very often connected to networks using wireless links
An ATM network interface in the form of an accessory card. A lot of network interfaces are built-in.
A typical home or small office router showing the ADSL telephone line and Ethernet network cable connections
Common network topologies
The TCP/IP model or Internet layering scheme and its relation to common protocols often layered on top of it.
Figure 4. Message flows (A-B) in the presence of a router (R), red flows are effective communication paths, black paths are across the actual network links.

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