Computer Networks and Internet Technology

Computer networks and Internet technology - This article gives a brief outline of foundation for networks, direct link networks, packet switching, internetworking, end-to-end protocols, resource allocation issues, and applications.

Contents

Computer networks

When two or more computers are interconnected to each other via some kind of medium to share resources then the state is called computer network.

Connection method

Computer networks can also be classified according to the hardware and software technology that is used to interconnect the individual devices in the network, such as Optical fiber, Ethernet, Wireless LAN, HomePNA, Power line communication or G.hn. Ethernet uses physical wiring to connect devices. Frequently deployed devices include hubs, network switches, network bridges and/or routers.

Wireless LAN technology is designed to connect devices without wiring. These devices use radio waves or infrared signals as a transmission medium.

Ethernet over coax 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.

Wired technologies

Twisted pair - This is the most widely used medium for telecommunication. Twisted-pair wires are ordinary telephone wires which consist of two insulated copper wires twisted into pairs and are used for both voice and data transmission. The use of two wires twisted together helps to reduce crosstalk and electromagnetic induction. The transmission speed range from 2 million bits per second to 100 million bits per second.

Coaxial cable – These cables are widely used for cable television systems, office buildings, and other worksites for local area networks. The cables consist of copper or aluminum wire wrapped with insulating layer typically of a flexible material with a high dielectric constant, all of which are surrounded by a conductive layer. The layers of insulation help minimize interference and distortion. Transmission speed range from 200 million to more than 500 million bits per second.

Fiber optics – These cables consist of one or more thin filaments of glass fiber wrapped in a protective layer. It transmits light which can travel over long distance and higher bandwidths. Fiber-optic cables are not affected by electromagnetic radiation. Transmission speed could go up to as high as trillions of bits per second. The speed of fiber optics is hundreds of times faster than coaxial cables and thousands of times faster than twisted-pair wire.[1]

Wireless technologies

Terrestrial microwave – Terrestrial microwaves use Earth-based transmitter and receiver. The equipment look similar to satellite dishes. Terrestrial microwaves use low-gigahertz range, which limits all communications to line-of-sight. Path between relay stations spaced approx. 30 miles apart. Microwave antennas are usually placed on top of buildings, towers, hills, and mountain peaks.

Communications satellites – The satellites use microwave radio as their telecommunications medium which are not deflected by the Earth's atmosphere. The satellites are stationed in space, typically 22,000 miles 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 are divided to different geographic area. Each area has low-power transmitter or radio relay antenna device to relay calls from one area to the next area.

Wireless LANs – Wireless local area network 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. Example of open-standard wireless radio-wave technology is IEEE 802.11b.

Bluetooth – A short range wireless technology. Operate at approx. 1Mbps with range from 10 to 100 meters. Bluetooth is an open wireless protocol for data exchange over short distances.

The wireless Web – The wireless web refers to the use of the World Wide Web through equipments like cellular phones, pagers, PDAs, and other portable communication devices. The wireless web service offers anytime/anywhere connection.

Scale

Networks are often classified as LAN, WAN, MAN, PAN, VPN, CAN, SAN, etc. depending on their scale, scope and purpose. Usage, trust levels and access rights often differ between these types of network - for example, LANs tend to be designed for internal use by an organization's internal systems and employees in individual physical locations (such as a building), while WANs may connect physically separate parts of an organization to each other and may include connections to third parties.

Functional relationship (network architecture)

Computer networks may be classified according to the functional relationships which exist among the elements of the network, e.g., Active Networking, Client-server and Peer-to-peer (workgroup) architecture.

Network topology

Network Topologies examples

Computer networks may be classified according to the network topology upon which the network is based, such as bus network, star network, ring network, mesh network, star-bus network, tree or hierarchical topology network. Network topology signifies the way in which devices in the network see their logical relations to one another. The use of the term "logical" here is significant. That is, network topology is independent of the "physical" layout of the network. Even if networked computers are physically placed in a linear arrangement, if they are connected via a hub, the network has a Star topology, rather than a bus topology. In this regard the visual and operational characteristics of a network are distinct; the logical network topology is not necessarily the same as the physical layout. Networks may be classified based on the method of data used to convey the data, these include digital and analog networks.

OSI-ISO Model

The Open System Interconnection Reference Model (OSI Reference Model or OSI Model) is an abstract description for layered communications and computer network protocoldesign. It was developed as part of the Open Systems Interconnection (OSI) initiative.[1 In its most basic form, it divides network architecture into seven layers which, from top to bottom, are the Application, Presentation, Session, Transport, Network, Data-Link, and Physical Layers. It is therefore often referred to as the OSI Seven Layer Model.

A layer is a collection of conceptually similar functions that provide services to the layer above it and receives service from the layer below it. On each layer an instance provides services to the instances at the layer above and requests service from the layer below. For example, a layer that provides error-free communications across a network provides the path needed by applications above it, while it calls the next lower layer to send and receive packets that make up the contents of the path. Conceptually two instances at one layer are connected by a horizontal protocol connection on that layer.

General communication model

General Communication Model

Communication model

The parts of this model are as follows:

Sender: The sender is what or who is trying to send a message to the receiver.

Encoder: In the general case, it is not possible to directly insert the message onto the communications medium. For instance, when you speak on the telephone, it is not possible to actually transmit sound (vibrations in matter) across the wire for any distance. In your phone is a microphone, which converts the sound into electrical impulses, which can be transmitted by wires. Those electrical impulses are then manipulated by the electronics in the phone so they match up with what the telephone system expects.

Message: Since this is a communication engineer's model, the message is the actual encoded message that is transmitted by the medium.

Medium: The medium is what the message is transmitted on. The phone system, Internet, and many other electronic systems use wires. Television and radio can use electromagnetic radiation. Even bongo drums can be used as a medium .

Decoder: The decoder takes the encoded message and converts it to a form the receiver understands, since for example a human user of the phone system does not understand electrical impulses directly.

Receiver: The receiver is the target of the message.

References

  1. ^ Hallberg, Bruce A. (2005). Networking: a beginner's guide. McGraw-Hill Professional. pp. 49–52. ISBN 0072262125. http://books.google.com/books?id=RzeAWg6XZaQC&printsec=frontcover. 

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