What is bridge in computer networking?

Segmenting a large network with a network device has numerous benefits. Among these are reduced collisions (in an Ethernet network), contained bandwidth utilization, and the ability to filter out unwanted packets. However, if the addition of the interconnect device required extensive reconfiguration of stations, the benefits of the device would be outweighed by the administrative overhead required to keep the network running. Bridges were created to allow network administrators to segment their networks transparently. This means that individual...

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What are the functions of Repeaters

All types of network connections suffer from attenuation and pulse distortion. For a given cable specification and bit rate, each has a maximum length of cable. Repeaters can be used to increase the maximum interconnection length and will do the following: Functions of Repeaters Clean signal pulses. Pass all signals between attached segments. Boost signal power. Possibly translate between two different media types (e.g., fiber – optic to twisted – pair cable...

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Stop and Wait Protocol

The sender allows one message to be transmitted, checked for errors and an appropriate ACK (Affirmative Acknowledgement) or NAK (Negative Acknowledgement) returned to the sending station. No other data messages can be transmitted until the receiving station sends back a reply, thus the name STOP and WAIT is derived from the originating station sending a message, stopping further transmission and waiting for a reply. Its major drawback is the...

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Frequency Division & Time Division Multiplexing

Frequency Division Multiplexing (FDM) In FDM the frequency spectrum is divided to form logical channels with each user having exclusive possession of the assigned channel. Time Division Multiplexing (TDM) In TDM, the users take turns (in a round robin); each one is periodically getting the entire bandwidth for the allotted time. Television broadcasting provides an example of multiplexing. Each TV channel operates in a different frequency range, which is a portion of the allocated spectrum, with the inter-channel separation great enough...

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What is Multiplexing?

In communication, Multiplexing is a technique that transmits signals from several sources over a single communication channel. So in order to minimize the cost of communication bearer, various techniques of sharing a communication channel between several users have been devised. These are known as multiplexing technique...

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Broadband Coaxial Cable

The other kind of coaxial cable systems uses analog transmission on standard cable television cabling. These can be used for digital data transfer also. It is cabled broadband. Although the term “broadband” comes from the telephone world, where it refers to anything wider than 4 kHz, in the computer networking world “broadband cable” means any cable network using analog transmission. Since broadband networks use standard cable television technology, the cables can be used up to 300 MHz (and often up to 450 MHz) and can run for nearly 100 km...

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Baseband Coaxial Cable

Another communication transmission medium is the coaxial cable. It has better shielding than twisted pairs, so it can span longer distances at higher speeds. Two kinds of coaxial cable are widely used. One kind, 50-ohm cable is commonly used for digital transmission and is the subject of this section. The other kind, 75-ohm cable, is commonly used for analog transmission and will be described in the next section. This distinction is based on historical, rather than technical factor, (e.g., early dipole antennas had an impedance of 300 ohms, and...

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Twisted Pair Cables

The oldest and still most common transmission medium is twisted pair. A twisted pair consists of two insulated copper wires, typically about 1 mm thick. The wires are twisted together in a helical form. The purpose of twisting the wires is to reduce electrical interference from similar pairs close by. The most common application of the twisted pair is the telephone systems. Twisted pairs can be used for either analog or digital transmission. The...

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Relationship between Data Rate and Bandwidth

The concept of effective bandwidth is somewhat fuzzy one. It is the band within which most of the energy is confined. The term “most” in this context is somewhat arbitrary. The important issue here is that, although a given waveform may contain frequencies over a broad range, as a practical matter any transmission medium that is used will be able to accommodate only a limited band of frequencies. This, in turn, limits the data rate that can be carried on the transmissio...

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Difference between Continuous & Discrete Signals

A continuous signal is one in which the signal amplitude or intensity varies in smooth fashion over time. There are no breaks or discontinuities in the signal. A discrete signal is one in which the signal intensity maintains a constant level for some period of time and then changes to another constant leve...

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Classification of Transmission Media

Transmission media may be classified in Two broad categories namely Guided & Unguided. In both cases, communication is in the form of electromagnetic waves. With guided media, the waves are guided along a physical path; examples of guided media are twisted pair, coaxial cable, and optical fiber. Unguided media provide a means for transmitting electromagnetic waves but do not guide them; examples are propagation through air, vacuum and seawater. The term direct link is used to refer to the transmission path between two devices in...

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Token Bus: IEEE Standard 804

IEEE Standard 804 (Token Bus) uses highly reliable cable envision equipments which is available from numerous vendors. It uses tokens to allow stations for start of transmission. It is more deterministic than IEEE Standard 802.3 although repeated losses of the token at critical moments can introduce more uncertainty than its supporters like to admit. Token Bus also supports priorities....

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Difference between OSI & TCP Reference Model

Following is the six basic differences between OSI Reference Model & TCP/IP Reference Model. OSI Reference ModelSeven layers It distinguishes between service, interface, and protocol. Firstly description of model and protocol came next Both have Network Supports connectionless and connection oriented communication in network layer and only connection-oriented communication in transport layer. Protocol in OSI model are better hidden and can be replaced relatively easily (No Transparency). TCP Reference ModelFour layers Did not clearly distinguish...

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TCP/IP Network Architecture & Reference Model

The TCP/IP network architecture is a set of protocols that allow communication across multiple diverse networks. The architecture evolved out of research that had the original objective of transferring packets across three different packet networks: the ARPANET packet-switching network, a packet radio network, and a packet satellite network. The military orientation of the research placed a premium on robustness with regard to failures in the...

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Difference between Broadcasting & Multicasting

Broadcasting refers to addressing a packet to all destinations in a network whereas multicasting refers to addressing a packet to a subset of the entire networ...

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Functions of Application Layer

Application Layer supports functions that control and supervise OSI application processes such as start/maintain/stop application, allocate or keep OSI resources, accounting, check point and recovering. It also supports remote job execution, file transfer protocol, message transfer and virtual termina...

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Presentation Layer Services & Functions

Unlike all the lower layers, which are just interested in moving bits reliably from here to there, the presentation layer is concerned with the syntax and semantics of the information transmitted. A typical example of a presentation service is encoding data in a standard agreed upon way. Most user programs do not exchange random binary bit strings, they exchange things such as people’s names, dates, amounts of money and invoices. These items are represented as character strings, integers, floating-point number, and data structures composed...

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Session Layer Functions & Services

The main tasks of the session layer are to provide: Session Establishment Session Release – Orderly or abort Synchronization Data Exchange Expedited Data Exchange The session layer allows users on different machines to establish sessions between them. A session allows ordinary data transport, as does the transport layer, but it also provides enhanced services useful in some applications. A session might be used to allow a user to log into a remote time-sharing system or to transfer a file between two machines. One of the services of the session...

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Functions of Transport Layer

The basic function of the transport layer is to accept data from the session layer, split it up into smaller units if need be, pass these to the network layer, and ensure that the pieces all arrive correctly at the other end. Furthermore, all this must be done efficiently, and in a way that isolates the upper layers from the inevitable changes in the hardware technology. Transport Layer provides location and media independent end-to-end data transfer service to session and upper layers. Functions of Transport Layer:  Segmentation Segment...

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Functions of Network Layer

The network layer ensures that each packet travels from its sources to destination successfully and efficiently. A key design issue is determining how packets are routed from source to destination. Routes can be based on static tables that are “wired into” the network and rarely changed. They can also be determined at the start of each conversation, for example a terminal session. Finally, they can be highly dynamic, being determined anew for each packet, to reflect the current network load. When a packet has to travel from one network to...

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Functions of Data Link Layer

The main task of the data link layer is to provide error free transmission. It accomplishes this task by having the sender configure the input data into data frames, transmit the frames sequentially, between network devices and process the acknowledgement frames sent back by the intermediate receiver. The data link layer creates and recognizes frame boundaries. This can be accomplished by attaching special bit patterns to the beginning and end of the frame. Since these bit patterns can accidentally occur in the data, special care must be taken...

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Functions of OSI Physical Layer

Physical Layer defines electrical and mechanical specifications of cables, connectors and signaling options that physically links two nodes on a network. The major functions and services performed by the physical layer are: Bit-by-bit or symbol-by-symbol delivery Providing a standardized interface to physical transmission media, including Mechanical specification of electrical connectors and cables, for example maximum cable length Electrical specification of transmission line signal level and impedance Radio interface, including electromagnetic...

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Physical Layer of OSI

Physical Layer defines electrical and mechanical specifications of cables, connectors and signaling options that physically links two nodes on a network. The physical layer or layer 1 is the first and lowest layer in the seven-layer OSI model of computer networking. The implementation of this layer is often termed PHY. The physical layer consists of the basic hardware transmission technologies of a network. It is a fundamental layer underlying the logical data structures of the higher level functions in a network. Due to the plethora of available...

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OSI (Open Systems Interconnection) Reference Model

The OSI model is based on a proposal developed by the International Standards Organization as a first step towards international standardization of the protocols used in the various layers. The model is called the ISO - OSI (International Standard Organization - Open Systems Interconnection) Reference Model because it deals with connecting open systems — that is, systems that follow the standard are open for communication with other systems, irrespective...

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What is Multicasting?

Broadcast networks have a single communication channel that is shared by all the machines on the network. Short messages, called packets sent by any machine are received by all the others. An address field within the packet specifies for whom it is intended. Upon receiving a packet, a machine checks the address field. If the packet is intended for itself, it processes the packet; if the packet is intended for some other machine, it is just ignored. Some broadcast systems also support transmission to a subset of the machines, something known as...

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Broadcast Networks and Broadcasting

Broadcast systems generally allow the possibility of addressing a packet to all destinations by using a special cod e in the address field. When a packet with this code transmitted, it is received and processed by every machine on the network. This mode of operation is called broadcasting. Broadcast networks have a single communication channel that is shared by all the machines on the network. Short messages, called packets sent by any machine are received by all the others. An address field within the packet specifies for whom it is intended....

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Ring Topology

In a ring topology, each device has a dedicated point to point line configuration only with the two devices on either side of it. A signal is passed along the ring in one direction from device to device, until it reaches its destination. Each device in the ring incorporates a repeater. When a device receiver a signal intended for another device, its repeater regenerates the bits and passes them along. A ring is relatively easy to install and...

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Tree Topology

A tree topology is a variation of a star. As in a star, modes in a tree are linked to a central hub that controls the traffic to the network. However, not every device plugs directly into the central hubs. The majority of devices connect to a secondary hub that in turn is connected to the central hubs. The advantage and disadvantages of a tree topology are generally the same as those of star. The addition of secondary hubs, however, brings...

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Star Topology

In a star topology, each device has a dedicated point to point link only to a central controller, usually called a hub. These devices are not linked to each other. If one device wants to send data to another, it sends to the hub, which then relays the data to the other connected devices. In a star, each device needs only one link and one I/O Port to connect it to any number of other devices. This factor makes it easy to install and reconfigure....

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Point to Point Network or Switched Networks

Point-to-point networks consist of many connections between individual pairs of machines. Data is usually transferred in relatively small fragments called packets (units bits or bytes). To go from the source to the destination, a packet on this type of networks may have to first visit one or more intermediate routers. When a packet is sent from one router to another intermediate routers, the entire packet is stored at each intermediate router till the output line is free and then forwarded. A subnet using this principle is called point to point...

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Applications of Computer Networks

The following is the list of some applications of computer network. Generic applications Resource sharing (CPU, peripherals, information and software) Personal communication (text + graphics + audio + video + data) Network-wide information discovery and retrieval Some Specific end applications Campus-wide computing and resources sharing Collaborative research and development Integrated system for design + manufacturing + inventory Electronic commerce, publishing and digital libraries Multi-media communication (tele-training, etc.) Health-care...

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Goals or Objective of Computer Network

The main goal of a computer network is to enable its users to share resources and to access these resources (i.e. hard disks, high quality expensive laser printer, modems, peripheral devices, licensed software, etc.), regardless of their physical locations. Physical locations may be a few feet or even thousands of miles apart, but users exchange data and programs in the same way. In other words, distance is removed as barrier for the above application. The computer network thus creates a global environment for its users and computers. Other goal...

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Wide Area Network (WAN)

Wide Area Network provides no limit of distance. In most WANs, the subnet consists of two distinct components. Transmission lines also called circuits or channels or links and switching and routing devices (switches & routers). Transmission-lines are used for moving bits between machines, whereas routers are used to connect two or more transmission lines. A WAN provides long distance transmission of data, voice, image and video information over large geographical areas that may comprise a country, a continent or even the whole world. In...

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Metropolitan Area Network (MAN)

Metropolitan Area Network is defined for less than 50 km. and provides regional connectivity typically within small geographical area. It is designed to extend over an entire city. It may be a single network such as cable television, network, or it may be a means of connecting a number of LANs into a large network, so that resources may be shared LAN to LAN as well as device to device. For example, a company can use a MAN to connect to the LANs in all of its offices throughout a city....

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Local Area Network (LAN)

What is Local Area Network (LAN)? A local area network is relatively smaller and privately owned network with the maximum span of 10 km. to provide local connectivity within a building or small geographical area. The LANs are distinguished from other kinds of networks by three characteristics: Size Transmission technology, and Topology Accordingly, there are many LAN standards such as IEEE standards 802...

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What is a Computer Network?

In the simplest form, data transfer can take place between two devices which are directly connected by some form of communication medium. But it is not practical for two devices to be directly point to point connected. This is due to the following reasons: The devices are very far apart. There is a set of devices, each of whom may require connecting to others at various times. Solution to this problem is to connect each device to a communication network. Computer Networks means interconnected set of autonomous systems that permit distributed...

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