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AbbreviationsO ANSI: American National Standards
InstituteO WWW: World Wide WebO CPU: Central Processing UnitO HDX: Half DuplexO FDX: Half DuplexO CB radio: Citizens' Band radioO UTP : Unshielded twisted pair
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Computer NetworkingDefinition: O A computer network, often simply
referred to as a network, is a collection of hardware components and computers interconnected by communications channels that allow sharing of resources and information.
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Applications of Networks
Resource SharingHardware (computing resources, disks, printers)Software (application software)
Information SharingEasy accessibility from anywhere (files, databases)Search Capability (WWW)
CommunicationEmailMessage broadcast
Remote computingDistributed processing (GRID Computing)
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AdvantagesOFile sharing.OResource sharing.OIncrease storage capacity.
OIncrease cost efficiency.
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DisadvantagesOSecurity issues.ORapid spread of computer virus.
OExpenses set-up.ODependency of main file server.
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Type Of TransmissionO Simplex
O Half DuplexO Full Duplex
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SimplexSimplex communication refers to communication that occurs in one direction only.O ANSI definition: A simplex circuit is one where all signals can
flow in only one direction. These systems are often employed in broadcast networks, where the receivers do not need to send any data back to the transmitter/broadcaster.
ExamplesO Commercial Radio Broadcast (not walkie-talkies, etc.)O Television BroadcastO Keyboard to CPU communicationO One-way communications from a launcher to a guided missile,
where the launcher (airplane, ship, etc.) sends commands to the missile, but does not receive any information sent back.
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Simplex (Continued..)
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Half DuplexDefinition:O A half-duplex (HDX) system provides
communication in both directions, but only one direction at a time (not simultaneously).
Typically, once a party begins receiving a signal, it must wait for the transmitter to stop transmitting, before replying.
Example: Walkie-talkie Fax Machine
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Full-DuplexO A full-duplex (FDX), or sometimes double-duplex system,
allows communication in both directions, and, unlike half-duplex, allows this to happen simultaneously.
It is a system composed of two connected parties or devices that can communicate with one another in both directions. (The term multiplexing is also used when describing communication between more than two parties or devices.)
Examples: Land-line telephone networks are full-duplex, since they allow both callers to speak and be heard at the same time. A good analogy for a full-duplex system would be a two-lane road with one lane for each direction.
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Full-DuplexExamples:O Telephone networksO Mobile phone networksO CB radioO Internet
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How many kinds of Networks?We can classify networks in different ways…
• Based on Transmission Media: Wired (UTP, coaxial cables, fiber-optic cables) and Wireless
• Based on Network Size: LAN and WAN (and MAN)• Based on Management Method: Peer-to-peer and
Client/Server• Based on Topology (connectivity): Bus, Star, Ring, Mesh,
Hybrid…
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Transmission MediaO Twisted Pair Cable
O Coaxial cablesO Fiber-optic cables
O Wireless
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Twisted Pair CableO Twisted pair cabling is a type of wiring in
which two conductors (the forward and return conductors of a single circuit) are twisted together for the purposes of cancelling out electromagnetic interference (EMI) from external sources; for instance, electromagnetic radiation from unshielded twisted pair (UTP) cables, and crosstalk between neighbouring pairs. It was invented by Alexander Graham Bell.
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Twisted Pair CableAdvantages:O High availability—More than 1 billion telephone
subscriber lines based on twisted-pair have been deployed, and because it's already in the ground it can be used.
O Low cost of installation on premises—The cost of installing twisted-pair on premises is very low.
O It is a thin, flexible cable that is easy to string between walls.
O More lines can be run through the same wiring ducts.
O UTP costs less per meter/foot than any other type of LAN cable.
O Electrical noise prevented- Electrical noise going into or coming from the cable can be prevented.
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Twisted Pair CableDisadvantages:O Limited frequency spectrum—The total usable
frequency spectrum of twisted-pair copper cable is about 1MHz.
O Limited data rates—The longer a signal has to travel over twisted-pair, the lower the data rate. At 30 feet (100 m), twisted-pair can carry 100Mbps, but at 3.5 miles (5.5 km), the data rate drops to 2Mbps or less.
O Short distances required between repeaters—More components need to be maintained, and those components are places where trouble can arise, which leads to higher long-term operational costs.
O High error rate—Twisted-pair is highly susceptibility to signal interference.
Coaxial CablesO Coaxial cable, or coax, is an electrical
cable with an inner conductor surrounded by a flexible, tubular insulating layer, surrounded by a tubular conducting shield. The term coaxial comes from the inner conductor and the outer shield sharing the same geometric axis. Coaxial cable was invented by English engineer and mathematician Oliver Heaviside, who patented the design in 1880.
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Coaxial CablesAdvantages:O Broadband system: Coax has a sufficient frequency
range to support multiple channels, which allows for much greater throughput.
O Greater bandwidth: Compared to twisted-pair, coax provides greater bandwidth, and it also offers greater bandwidth for each channel. As it has greater bandwidth per channel, it supports a mixed range of services. Voice, data, and even video and multimedia can benefit from the enhanced capacity.
O Lower error rates: Because the inner conductor is in a shield insulator, noise immunity is improved, and coax has lower error rates and therefore slightly better performance than twisted-pair. The error rate is generally 10-9 (i.e., 1 in 1 billion) bps.
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Coaxial CablesDisadvantages:O Problems with the deployment
architecture: The bus topology in which coax is deployed is susceptible to congestion, noise, and security risks.
O High installation costs: Installation costs in the local environment are high.
O Bidirectional upgrade required: In countries that have a history of cable TV, the cable systems were designed for broadcasting, not for interactive communications. Before they can offer to the subscriber any form of two-way services, those networks have to be upgraded to bidirectional systems.
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Fiber-Optic CablesO An optical fiber cable is a cable containing
one or more optical fibers. The optical fiber elements are typically individually coated with plastic layers and contained in a protective tube suitable for the environment where the cable will be deployed.
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Fiber-Optic Cables
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Fiber-Optic CablesAdvantages:O Extremely high bandwidth – No other cable-
based data transmission medium offers the bandwidth that fiber does.
O Resistance to electromagnetic interference – Fiber has a very low rate of bit error (10 EXP-13), as a result of fiber being so resistant to electromagnetic interference. Fiber-optic transmission are virtually noise free.
O Early detection of cable damage and secure transmissions – Fiber provides an extremely secure transmission medium. By constantly monitoring an optical network and by carefully measuring the time it takes light to reflect down the fiber, splices in the cable can be easily detected.
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Fiber-Optic CablesDisadvantages:O Installation costs are still high – Despite the fact
that fiber installation costs are dropping by as much as 60% a year, still installing fiber optic cabling is relatively costly.
O Special test equipment is often required – The traditionally used test equipment are of no use. Equipment such as an OTDR (Optical Time Domain Reflectometer) are used.
O Susceptibility to physical damage – Fiber is a small and compact cable, and it is highly susceptible to becoming cut or damaged during installation or construction activities.
O Wildlife damage to fiber optic cables – Fibre optic cable (fiber cable jackets particularly) is made of using many Wildlife materials such as Bird’s nest.
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WirelessO Wireless network refers to any type of computer
network that is not connected by cables of any kind. It is a method by which homes, telecommunications networks and enterprise (business) installations avoid the costly process of introducing cables into a building, or as a connection between various equipment locations. Wireless telecommunications networks are generally implemented and administered using a transmission system called radio waves.
Example: WiMAX (Wireless MAN)
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WirelessWireless communications can be via:O Radio frequency communicationO Microwave communication, for example long-range
line-of-sight via highly directional antennas, or short-range communication,
O Infrared (IR) short-range communication, for example from consumer IR devices such as remote controls.
O Wi-Fi is a wireless local area network that enables portable computing devices to connect easily to the Internet. Standardized as IEEE 802.11 a,b,g,n, Example: Internet access at private homes, within offices, and at public hotspots.
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WirelessO Cellular data service offers effective coverage within a range of
10-15 miles from the nearest cell site. Speeds have increased as technologies have evolved, from earlier technologies such as GSM, CDMA and GPRS, to 3G networks such as W-CDMA, EDGE or CDMA2000.
O Mobile Satellite Communications may be used where other wireless connections are unavailable, such as in largely rural areas or remote locations. Satellite communications are especially important for transportation, aviation, maritime and military use.
O Bluetooth is a proprietary open wireless technology standard for exchanging data over short distances (using short wavelength radio transmissions in the ISM band from 2400-2480 MHz) from fixed and mobile devices, creating personal area networks(PANs) with high levels of security. Created by telecoms vendor Ericsson in 1994, it was originally conceived as a wireless alternative to RS-232 data cables. It can connect several devices, overcoming problems of synchronization.
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Network TropologyDefinition: The network topology defines the way in which computers, printers, and other devices are connected. A network topology describes the layout of the wire and devices as well as the paths used by data transmissions
Types:O Bus TropologyO Ring TropologyO Star TropologyO Mesh Tropology
O Hybrid Tropology
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Bus TropologyO A bus network topology is a network
architecture in which a set of clients are connected via a shared communications line, called a bus. There are several common instances of the bus architecture, including one in the motherboard of most computers, and those in some versions of Ethernet networks.
Bus Topology
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Ring TropologyO A ring network is a network topology in
which each node connects to exactly two other nodes, forming a single continuous pathway for signals through each node - a ring. Data travels from node to node, with each node along the way handling every packet.
Ring Topology
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Star TropologyO Star networks are one of the most
common computer network topologies. In its simplest form, a star network consists of one central switch, hub or computer, which acts as a conduit to transmit messages. This consists of a central node, to which all other nodes are connected; this central node provides a common connection point for all nodes through a hub.
Star Topology
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Mesh TropologyO The type of network topology in which
some of the nodes of the network are connected to more than one other node in the network with a point-to-point link – this makes it possible to take advantage of some of the redundancy that is provided by a physical fully connected mesh topology without the expense and complexity required for a connection between every node in the network.Mesh
Topology
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Hybrid TropologyO Hybrid networks use a combination of any two
or more topologies in such a way that the resulting network does not exhibit one of the standard topologies (e.g., bus, star, ring, etc.).
For example, a tree network connected to a tree network is still a tree network topology. A hybrid topology is always produced when two different basic network topologies are connected. Two common examples for Hybrid network are: star ring network and star bus network
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Hybrid Tropology(Continued…)
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LAN (Local Area Network)
O A local area network (LAN) is a computer network that interconnects computers in a limited area such as home, school, computer laboratory or office building.
It allows resource sharing between computers within a limited area.Example: Intranet of IMED.
Wifi Network of my House.
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MAN (Metropolitan Area Network)O A metropolitan area network (MAN) is
a computer network that usually spans a city or a large campus. A MAN usually interconnects a number of local area networks (LANs) using a high-capacity backbone technology, such as fiber-optical links, and provides up-link services to wide area networks (or WAN) and the Internet.
Example: Many Telcom Company provide a popular MAN service called SMDS (Switched Multimegabit Data Services).
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WAN (Wide Area Network)O A wide area network (WAN) is a
telecommunication network that covers a broad area (i.e., any network that links across metropolitan, regional, or national boundaries). Business and government entities utilize WANs to relay data among employees, clients, buyers, and suppliers from various geographical locations. In essence this mode of telecommunication allows a business to effectively carry out its daily function regardless of location.
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WAN (Wide Area Network)(Cont.…)
WAN
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InternetO The Internet is a global system of
interconnected computer networks that use the standard Internet Protocol Suite (TCP/IP) to serve billions of users worldwide. It is a network of networks that consists of millions of private, public, academic, business, and government networks, of local to global scope, that are linked by a broad array of electronic, wireless and optical networking technologies.
O Example: World Wide Web
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INTERNET
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IntranetO An intranet is a computer network that
uses Internet Protocol technology to securely share any part of an organization's information or network operating system within that organization.
Sometimes the term refers only to the organization's internal website.
Example: Intranet Of Bharati Vidyapeeth University
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ExtranetO An extranet is a computer network that
allows controlled access from the outside, for specific business or educational purposes. An extranet can be viewed as an extension of a company's intranet that is extended to users outside the company, usually partners, vendors, and suppliers.
Example: Bank’s Internet Banking
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