bbit 213 lecture 2

8/8/2019 Bbit 213 Lecture 2

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Lecture 2: Introduction to Networks

A network consists of multiple computers connectedusing some type of interface, each having one ormore interface devices such as a Network Interface

Card (NIC) and/or a serial device for PPP networking. Each computer is supported by network software that

provides the server or client functionality.

The hardware used to transmit data across thenetwork is called the media. It may include copper

cable, fiber optic, or wireless transmission. The standard cabling used for the purposes of this

document is 10Base-T category 5 ethernet cable.


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Network Categories

There are two main types of network categorieswhich are:

Server based

Peer-to-peer

In a server based network, there are computersset up to be primary providers of services such asfile service or mail service.

The computers providing the service are calledservers and the computers that request and use

the service are called client computers. In a peer-to-peer network, various computers on

the network can act both as clients and servers.


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Store-and-Forward Systems

Messages may be stored at intermediate nodes

along the transmission path between sender and

receiver in store-and-forward systems

This helps ensure message delivery withoutobligating the sender to wait until a message is

delivered before transmitting other messages

It also helps ensure message delivery in the case

of link or destination failure while the message is

in transit

Store-and forward algorithms are valuable in time-

staged delivery systems and in networks that

assign priorities to different messages


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Serial and Parallel transmission

The transmission mode refers to the number ofelementary units of information (bits) that can besimultaneously translated by the communications

channel. Parallel connection means simultaneous

transmission ofNbits. These bits are sentsimultaneously overNdifferent channels

Serial connection - the data are sent one bit at a

time over the transmission channel. However,since most processors process data in parallel, thetransmitter needs to transform incoming paralleldata into serial data and the receiver needs to dothe opposite.


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The parallel-serial transformation isperformed using a shift register. The shiftregister, working together with a clock, willshift the register (containing all of the datapresented in parallel) by one position to theleft, and then transmit the most significant bit(the leftmost one) and so on:

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Network Topology, Architecture, and

Complexity Network topologyrefers to the physical layout

of a network, the way that nodes attach to the

communication medium Network architecture refers to the way in

which media, hardware, and software areintegrated to form a network

Network complexityis concerned with extentto which network architectures are simple ordiverse in their make


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Network Topologies

Bus All Pcs connect to a common cable/bus. Bothends of the network must be terminated with aterminator.

Star - All devices revolve around a central hub,which is what controls the networkcommunications, and can communicate with otherhubs. Range limits are about 100 meters from thehub.

Ring - Devices are connected from one to anotherin a ring. A data token is used to grant permissionfor each computer to communicate.

Mesh - allow each computer to have a directconnection to each of the other computers.

There are also hybrid networks including a star-bushybrid, star-ring network, and tree networks withconnections between various computers on the

network.


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Reason for multiple topologies

Each topologies has advantages and

disadvantages. Give them.


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Telecom Channels

Channels - the links by which data orvoice are transmitted between sending

and receiving devices in a network twisted wires

coaxial cable

fiber-optic cable

wireless microwave

satellite


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Telecom Channels other Wireless

Cellular

Mobile data networks (2-way)

PCS (personal communication

systems)- to the end user acts like

cellular, but different

Personal data assistants


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Transmission Speeds

Medium Speed Cost

Twisted Wire 300 bps-10 Mbps Low

Microwave 256 Kbps-100 MbpsSatellite 256 Kbps-100 Mbps

Coaxial Cable 56 Kbps-200 Mbps

Fiber-Optic Cable 500 Kbps-10 Gbps High


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Transmission Media These transmission channels are made up of

several segments that allow the data to circulate inthe form of electromagnetic, electrical, light or evenacoustic waves.

In order for data to be exchanged, an encoding

must be chosen for the transmission signals. Thisdepends basically on the physical medium used totransfer the data, the guaranteed data integrity andtransmission speed.

Data transmission is called "simple" if there are

only two machines communicating, or if only asingle piece of data is sent. Otherwise, it isnecessary to install several transmission lines toshare the line among several differentcommunication actors. This sharing is called

multiplexing.


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COPPERWIRES

Conventional computers use copper wires as theprimary medium to connect computers becausethey are inexpensive and easy to install.

To minimize interference, networks use one oftwo basic wiring types:- twisted pair or coaxialcable

The simple twists change the electrical propertiesof the wire and make it suitable for use in a

network.- they limit electromagnetic energy thewire emits, the twists prevent electric currentfrom radiating energy that interferes with otherwires and others from interfering with its own.


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The jacketprotects the cable from the externalenvironment. It is usually made of rubber (or

sometimes Polyvinyl Chloride (PVC) or Teflon). The shield (metal envelope) surrounding the cables

protects the data transmitted on the medium frominterference (also called noise) that could corrupt thedata.

The insulator surrounding the central core is made ofa dielectric material that prevents any contact with theshield that could cause electrical interactions (shortcircuit).

The core, which actually transports the data, generally

consists of a single copper strand or of several braidedstrands.


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GLASS FIBERS Computers use flexible glass fibers called optical

fibers to transmit data

A transmitter at the end of one fiber uses LED orlaser to send pulses of light through the fiber

Advantages over copper wires:- They are not susceptible to electrical signal

interference

Carry pulses of light much farther that copper

Light can encode more information thanelectrical signals hence optical fiber can carrymore data.

Data from more than one source can betransmitted at a go.


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Disadvantages

Expensive and technically difficult to install andmaintain

If the fiber breaks internally, it is difficult to locatethe problem.

Radio Phones use electromagnetic waves to transmit

computer data.

A network that uses electromagnetic radio waves

is said to operate at a radio frequency andtransmissions are referred to as RF transmissions.

Each participating computer attaches an antennawhich can both transmit and receive RF signals.


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Satelites

A communications satellite (sometimesabbreviated to COMSAT) is an artificial satellitestationed in space for the purpose oftelecommunications.

Radio transmissions do not bend around the surfaceof the earth, RF is combined with satellites to give asolution to this.

The satellite contains a transponder which consists ofa radio receiver and transmitter.

The transponder accepts radio signals, amplify andtransmit the signal back at a different angle

A single satellite contains multiple transponders (sixto twelve) each using a different frequency making itpossible for multiple communications to proceedsimultaneously.


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Communication satellites can be grouped intotwo:- Geosynchronous and geostationary

Geosynchronous (GEO) is placed in an orbitthat is synchronized with the earth rotation.

The laws of physics are use to determine theexact distance 35 785 KM also called Highearth orbit

Thee is a limited amount of space available inthe orbit because they have to be separatedby some distance between them

The minimum separation distance dependson power of the transmitters generally 4 to 8degrees the entire equator can hold 45 to90


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Low earth Orbits (LEO)

They do not stay at a single location but travelaround the earth faster than the earth.

A single LEO can complete an entire orbit in 1.5

hrs. Having a satellite that does not appear stationary

causes problems

Can only be used during the time the orbitspass between two ground stations

Maximal utilization requires complex controlsystems that continuously move the groundstations

How are they therefore used?


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Microwave Electromagnetic waves beyond the radio and

television frequencies can be used totransport information.

Although they are a few frequencies higher

than radio frequencies they behave differently They can be aimed at a single direction.

They also carry more data at lower frequencytransmissions

Microwaves cannot penetrate metalstructures and work best under a clear pathbetween the transmitter and receiver


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Infrared

Infrared light lies between the visibleand microwave portions of the

electromagnetic spectrum.

It is limited in distance The transmitter must be pointed to

receiver and does not require an

antenna


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Data Communication

Frameworks Two major data communication

frameworks have been developed to

help ensure that networks meetbusiness and communicationrequirements:

Open Systems Interconnection (OSI)

reference model developed by theInternational Standards Organization (ISO)

Transmission Control Protocol/InternetProtocol (TCP/IP) suite


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Models of the Internet

OSI/ISO Reference Model TCP/IPReference Model

Open Systems Interconnection

(International Standards Office)

Application

PresentationSessionTransportNetworkData LinkPhysical

Model Layers

Application

TransportInternetHost-to-network

Transmission Control

Protocol/

Internet Protocol


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Summary

Data Communications Supports Applications

The Operating System manages the

resources of the computer.

There must however, be a system that

provides a bridge between applications and

the devices so they can communicatethis is

called a Transaction Control Process (TCP)

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