computer networks2003

7/31/2019 Computer Networks2003

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Computer Networks

Computer network connects two ormore autonomous computers.The computers can be geographicallylocated anywhere.

Two or more than two computersystems connected by means of acommunication medium like cablesis termed as a Network.Computer Network is acommunication systems, which linkscomputers and their resources.

Computer Resources are storagedevices e.g. HDD, tape drive,CDROM, MODEM,RDBMS likeOracle, MS-SQL etc and any othercomputing system (Mainframe,Minicomputer etc.).

Introduction to Computer Networks


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Resource Sharing

Hardware (computing resources, disks, printers)Software (application software)

Information SharingEasy accessibility from anywhere (files, databases)Search Capability (WWW)

CommunicationEmailMessage broadcast

Remote computing

Distributed processing (GRID Computing)

Service Access

Easy Back-Up Management

Security

Centralized Administration and Support

Advantages of a Network


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The network topology defines the way in which computers,printers, and other devices are connected.

A network topology describes the physical layout of the wireand devices as well as the paths used by data transmissions.The choice of the networks topology for installing a computernetwork depends upon a combination of factors, such as:

The desired performance of the system.

The desired reliability of the system.

Size of the system.

Expandability of the system.

Availability of communication lines.

Delays involved in routing information from one node toanother.

Network Topology


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Bus Topology

The bus topology refers to a linear arrangement ofcomputers that are connected together by a single

cable referred to as the trunk or backbone. It is

often used when a network installation is small,

simple or temporary.


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Advantages:

Simple,Reliable,Easy to use and understand.Least amount of cable to connect acomputers.

Easy to extend a bus with the help of arepeater.

Disadvantages

If the cable is broken from the middle the entirenetwork collapses

If the bus is long then packets may be lost.


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The star topology is the most

commonly used architecture inEthernet LANs.

When installed, the star topologyresembles spokes in a bicyclewheel.

Larger networks use the extendedstar topology also called treetopology.

When used with network devices

that filter frames or packets, likebridges, switches, and routers, thistopology significantly reduces thetraffic on the wires by sendingpackets only to the wires of thedestination host.

Star and Tree Topology


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Advantages:

Good PerformanceEasy to set up and to expand.

Any non-centralized failure will have verylittle effect on the network, whereas on a

ring network it would all fail with one fault.

Disadvantages:Expensive to install

Extra hardware requiredIf the host computer fails the entire system isaffected.


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A frame travels around the ring,stopping at each node. If a node wantsto transmit data, it adds the data aswell as the destination address to theframe.

The frame then continues around thering until it finds the destination node,which takes the data out of the frame.

Single ring All the devices on the

network share a single cable

Dual ring The dual ring topologyallows data to be sent in bothdirections.

Ring Topology


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Advantages:

Data is quickly transferred without a bottle neck.(very fast, all data traffic is in the same direction)

The transmission of data is simple as packets travel inone direction only.Adding additional nodes has very little impact onbandwidthIt prevents network collisions because of the mediaaccess method or architecture required.

Disadvantages:Data packets must pass through every computerbetween the sender and recipient therefore this makesit slower.

If any of the nodes fail then the ring is broken anddata cannot be transmitted successfully.It is difficult to troubleshoot the ring.Because all stations are wired together, to add a stationyou must shut down the network temporarily.In order for all computers to communicate with each

other, all computers must be turned on.


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Token Ring TopologyA token ring is a type of computer network in which all thecomputers are arranged (schematically) in a circle. A token,

which is a special bit pattern, travels around the circle. Tosend a message, a computer catches the token, attaches amessage to it, and then lets it continue to travel around thenetwork.

Although it is considered a more reliablesystem, a token ring network is slower and offers lessflexibility than schools and other businesses need. In a tokenring, only one computer may send information at a time.


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The mesh topologyconnects all devices(nodes) to each other forredundancy and faulttolerance.

It is used in WANs tointerconnect LANs and formission critical networkslike those used by banksand financial institutions.

Implementing the meshtopology is expensive anddifficult.

Introduction to Computer Networks

Mesh Topology


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Wired Network


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LAN (Local Area Network)

WAN (Wide Area Network)

Types of Network


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Network in small geographical Area

E.g. Room, Building or a Campus

Definition: LAN connects computers that are located neareach other or at the same location.

A corporate network consisting of several building in acampus an example of a LAN

LAN


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A local area network is a computer network across one

building or site.

Fileserver

Printer

Work Station

Network Cable

A Typical Local Area Network


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WIDE AREA NETWORKSLONG HAUL NETWORKS

WAN connects a numbers of computers which are located ata greater distance from one other or at different location.

Internet is an example of WAN

A WAN is a data communications network that covers arelatively broad geographic area and that often uses

transmission facilities provided by common carriers, such astelephone companies(coaxial cables) or communicationsatellites.

WAN uses no fixed Network Topology.

WAN


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Hybrid Network


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CAN (Campus Area Network)

MAN (Metropolitan Area Network)

HAN (Home Area Network)

Types of Network


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Network in a campus specific to an academic setting. iscalled as CAN

ALSO CALLED: Controller Area Network, or Cluster AreaNetwork

A network spanning multiple LANs but smaller than a MAN,such as on a university campus.

The main aim is to facilitate students accessing internet anduniversity resources.

CAN


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Network in a City is call MAN

Networks that share some of the characteristics of both

LANs and WANs are sometimes referred to as MAN.

The MANs usually cover a wider geographic area than LANs.

The main objective of MANs is to interconnect LANs located

in a entire city or metropolitan area.

MAN


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Network in a home is called as HAN

ALSO CALLED: Home Networks, Home Networking, HAN,Digital Home Networks, and Digital Home Networking

A home network allows computer owners to interconnectmultiple computers so that each can share files, programs,printers, other peripheral devices, and Internet access withother computers, reducing the need for redundantequipment and, in general, making everything easier to use.

A new trend, sometimes referred to as an intelligentnetwork, extends the home network to include controls forthe home ambient environment, security systems, andkitchen devices which in future will be controlled remotely.

HAN


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Hybrid Networks: Wired vs. WirelessWired Network Wireless Network

Fast Slow

Stationary Mobile

Flexibility depends on the wired length Flexibility

Only the devices connected can access Wider devices can access, e.g. PDA

Expensive to set up Cheaper to set up

Difficult to set up Easier to setup

Troubleshooting is difficult Troubleshooting is easier

More Secure Less Secure

Gaming, Share Files Streaming audio and video files

A hybrid network offers the best of both in terms of speed, mobility, affordability andsecurity.If a user needs maximum Internet speed, then he can plug into the network viaEthernet cable. If he needs to use internet in the hallway, he can access the networkwirelessly.With the right planning, an organisation can save money on Ethernet cable.With the right encryption and password management , the wireless portion of the

network can be made secure.


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Wireless Network


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IntranetAn internal corporate network built using Internet and World WideWeb standards and products that allows employees of anorganization to gain access to corporate information

ExtranetA network based on Web technologies that links selected resourcesof the intranet of a company with its customers, suppliers, or otherbusiness partners

Intranets and Extranets


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A network based an internet belonging to an organization,usually a corporate.

An Intranet does not extend beyond the organisation thatcreated it.

It is accessible only by the organization's members,employees, or others with authorization.An intranet's Web sites look and act just like any other Websites, but the firewall surrounding an intranet fends offunauthorized access.

Based on client server model

Intranet


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Like the Internet itself, intranets are used to shareinformation.

Secure intranets are now popular because they aremuch less expensive to build and manage.

Low cost distribution of internal corporateinformation

Intranets can also be used to provide softwareupdates and patches, which update userscomputers automatically using scripts

Intranet Advantages


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Training

Provides online access to a host of training functionsincluding course catalogue, registration, content, andevaluation

Provides significant increases in productivity andstandardization, and cost reductions (e.g. travel costs)

Application IntegrationAllows for integration and consolidation of information fromdisparate systems into a single point of access

Increases employee productivity and output quality

Online Entry of InformationAllows for direct online input to streamline routine businessprocesses (e.g. expense reporting)

Provides for significant cost reductions from reducingadministrative support and shifting maintenance functionsback to the employee (e.g. updating 401K selections)

Intranet Applications


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Extranet is a type of intranet that is partially accessible toauthorized outsiders, members not belonging to theorganisation.

An extranet provides various levels of accessibility tooutsiders.

You can access an extranet only if you have a valid usernameand password, and your identity determines which parts ofthe extranet you can view.

Extranets are becoming a very popular means for businesspartners(of two different corporate or organisation) to

exchange information.

Extranet


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Networks that connect companies with suppliers,

business partners and authorised usersEach user has access to the databases, files and otherinformation stored on computers connected to theextranet

Improves timeliness and accuracy of communications

reducing errors and misunderstandingsAllows central management of documents allowingsingle updates which are then available to all interestedparties

Easy to use, requires little training

Used to automate transactions, reducing cost and cycletime

Fedex changed from an Intranet to Extranet for packagetracking on their Web site

Extranet Advantages


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Supply Chain Management

Used to exchange supply and manufacturing informationbetween customers and suppliers

The extranet contains features allowing participants topurchase online, check supplier inventory, transfer

design specifications, and other business related tasks

Trading Exchanges (Electronic Marketplaces)

Allow many buyers and many sellers to come togetherOffer transaction processing, industry information, bestsourcing, info resources, and invoicing

Revenues made through advertising and transaction fees

Extranet Applications


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Virtual Private Network, is a network that is constructed byusing public wires to connect nodes.

For example, there are a number of systems that enable youto create networks using the Internet as the medium fortransporting data.

These systems use encryption and other securitymechanisms to ensure that only authorized users can accessthe network and that the data cannot be intercepted.

The connection is virtual since it is only temporary, it iscreated when information needs to be transmitted

A VPN is an extranet, but not every extranet is a VPN

VPN


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In this structure there is one computer or

workstation assigned as a server or master and thatprovides services or controls the other workstationsor clients.

There are 2 types

Master/Slave

Client/Server

Master SlaveMaster/slave is a model for a communication protocol inwhich one device or process (known as the master)controls one or more other devices or processes (knownas slaves).

Once the master/slave relationship is established, thedirection of control is always from the master to theslave(s).

Some manufacturers prefer the term primary/secondary.

Network Structures Server Based


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Client/server describes the relationship betweentwo computer programs in which one program, the

client, makes a service request from anotherprogram, the server, which fulfills the request.

In a network, this model provides a convenient wayto interconnect programs that are distributedefficiently across different locations.

In the Internet, your Web browser is a clientprogram that requests services (the sending of Web

pages or files) from a Web server in anothercomputer somewhere on the Internet.

The server contains the file, print, application,security, and other services in a central computerthat is continuously available to respond to clientrequests.

For example, to check your bank account from your

computer, a client program in your computerforwards your request to a server program at thebank. That program may in turn forward the requestto its own client program that sends a request to adatabase server at another bank computer toretrieve your account balance. The balance isreturned back to the bank data client, which in turn

serves it back to the client in your personalcomputer, which displays the information for you.

Network Structures Client Server


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Peer-to-peer is a communications model inwhich each party has the same capabilities

and either party can initiate a communicationsession.

In some cases, P2P communications isimplemented by giving each communicationnode both server and client capabilities.

In recent usage, P2P has come to describe

applications in which users can use theInternet to exchange files with each otherdirectly or through a mediating server.

On the Internet, P2P is a type of transientnetwork that allows a group of computerusers with the same software to connect witheach other and directly access files from one

another's hard drives. E.g Napster, Limewire

Corporations are looking at the advantages ofusing P2P as a way for employees to sharefiles without the expense involved inmaintaining a centralized server and as a wayfor businesses to exchange information witheach other directly.

Network Structures Peer to Peer
http://upload.wikimedia.org/wikipedia/commons/3/3f/P2P-network.svg


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How Does Internet P2P Work?

The user must first download and execute a peer-to-peer networking program.

After launching the program, the user enters the IPaddress of another computer belonging to thenetwork.Once the computer finds another network memberon-line, it will connect to that user's connection (whohas gotten their IP address from another user'sconnection and so on).

Users can choose how many member connections toseek at one time and determine which files they wishto share or password protect.

Network Structures Peer to Peer


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physical link: transmitted data bit propagates across link

Guided or wired media:signals propagate in solid media: copper, fiber

unguided or wireless media:signals propagate freely .eg., radio or infrared

signal carried in electromagnetic spectrum

no physical wire

bidirectional

propagation environment effects:reflection

obstruction by objects

interference

Network Media


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Twisted Pair (TP)two insulated copper wires

Category 3: traditional phone wires, 10 Mbps ethernet

Category 5 TP: 100Mbps ethernet

DrawbacksUnidirectional

Data loss due to no insulation

Network Media - Wired


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Coaxial cable:

wire (signal carrier) within a wire (shield)

baseband: single channel on cable

broadband: multiple channel on cablebidirectional

common use in 10Mbs Ethernet

The error rate is less than coaxial but more than Fiber Optic



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Fiber optic cable:glass fiber carrying light pulses

high-speed operation:

100Mbps Ethernet

high-speed point-to-point transmission (e.g., 5 Gps)

low error rate


k d l


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Radio

10 Khz to 1 Ghz.It is broken into many bands including AM, FM,and VHF bands.

Frequencies for unregulated use are:902-928Mhz - Cordless phones, remote controls.

2.4 Ghz

5.72-5.85 Ghz

Network Media - Wireless

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Microwave

Terrestrial

Used to link networks over long distances but the twomicrowave towers must have a line of sight betweenthem.

4-6GHz or 21-23GHz.

Speed is often 1-10MbpsThe signal is normally encrypted for privacy.

Satellite

A station on the ground will send and receive signalsfrom the satellite.

The signal can have propagation delays between 0.5 to5 seconds due to the distances involved.

The transmission frequency is normally 11-14GHz

Speed is in the range of 1-10Mbps.


k di i l


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Infared

Infared is just below the visible range of lightbetween 100Ghz and 1000Thz.

A light emitting diode (LED) or laser is used totransmit the signal.

The signal cannot travel through objects.

Light may interfere with the signal.


N k M di Wi l


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The types of infared are

Point to point

Transmission frequencies are 100GHz-1,000THz.Transmission is between two points and is limited toline of sight range.

It is difficult to eavesdrop on the transmission. The

speed is 100Kbps to 16Mbpsbroadcast

The signal is dispersed so several units may receive thesignal.

The unit used to disperse the signal may be reflectivematerial or a transmitter that amplifies and retransmitsthe signal.

The speed is limited to 1Mbps.

Transmission frequency is normally 100GHz-1,000THzwith transmission distance in 10's of meters.



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A network interface card (NIC) is a

computer circuit board or card that isinstalled in a computer so that it can beconnected to a network.

Each computer MUST have one of these.

It is the component that uniquelyidentifies the client or the server.

Personal computers and workstations ona local area network (LAN) typicallycontain a NIC specifically designed for the

LAN transmission technology, such asEthernet or Token Ring.

NIC provide a dedicated, full-timeconnection to a network.

Network Interface Card


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A hub is the central part of a star topology

The term is similar to airport "hubs" to make connecting flights fromone point to another.

In data communications, a hub is a place of convergence where dataarrives from one or more directions and is forwarded out in one or more

other directions.

A hub usually includes a switch of some kind. (And a product that iscalled a "switch" could usually be considered a hub as well.)

A hub can also include a router.

A hub may include a group of modem cards for dial-in users, a gatewaycard for connections to a local area network (for example, an Ethernetor a Token Ring), and a connection to a line (the main line in thisexample).

HUB


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A bridge is a device that connects one local area network (LAN) to another localarea network that uses the same protocol (for example, Ethernet or Token Ring).

If a data unit on one LAN is intended for a destination on an interconnected LAN,the bridge forwards the data unit to that LAN; otherwise, it passes it along onthe same LAN.

A bridge usually offers only one path to a given interconnected LAN.

In bridging networks, computer or node addresses have no specific relationshipto location. For this reason, messages are sent out to every address on thenetwork and accepted only by the intended destination node.

Bridges learn which addresses are on which network and develop a learningtable so that subsequent messages can be forwarded to the right network.

Drawback: Bridging networks are generally always interconnected local areanetworks since broadcasting every message to all possible destinations wouldflood a larger network with unnecessary traffic.

A bridge is sometimes combined with a router in a product called a brouter.

BRIDGES


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A switch is a single connection point for a group of computers.

A switch is a device that channels incoming data from any ofmultiple input ports to the specific output port that will takethe data toward its intended destination.

On a LAN, it determines from the physical device address ineach incoming message frame which output port to forward itto and out of.

In case of the Internet, a switch determines from the IPaddress in each packet which output port to use for the nextpart of its trip to the intended destination.

In the simplest networks, a switch is not required formessages that are sent and received within the network.

Switches


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A device that forwards data packets along networks.

A router is connected to at least two networks, commonlytwo LANs or WANs or a LAN and its ISPs network anddecides which way to send each information packet basedon its current understanding of the state of the networks itis connected to. .

Routers are located at gateways, the places where two ormore networks connect.

Routers choose the best route for data, based on the info inrouting table, out of a number of paths out to destinationson the various connected networks.

Very little filtering of data is done through routers.

Routers

GATEWAYS


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They are used for connecting networks that are built on totallydifferent communication architectures.

Definition: A node on a network that serves as an entrance toanother network.

In enterprises, the gateway is the computer that routes the trafficfrom a workstation to the outside network that is serving the Webpages. Also acts as a proxy server and a firewall.

In homes, the gateway is the ISP that connects the user to theinternet.

It also connects a computer system located on earth that switchesdata signals and voice signals between satellites and terrestrialnetworks.

An earlier term for router, though now obsolete in this sense as

router is commonly used.

GATEWAYS


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Definition

The standard local area network (LAN) access method. Areference to "LAN," "LAN connection" or "network card"automatically implies Ethernet.

Most new computers come network ready with Ethernet builtin. For machines without a network connection, Ethernet

adapters can be added via USB or PC Card or by plugging anEthernet card into a free PCI bus slot inside the case.

A 10/100 Ethernet port supports two speeds: 10 Mbps (10Base-T or Ethernet) and 100 Mbps (100Base-T or Fast Ethernet).

Computers also come with 10/100/1000 ports, which includes

Gigabit Ethernet at 1 Gbps (1,000 megabits).Ethernet devices negotiate with each other and transmit at thehighest speed possible. For high-speed backbones inmetropolitan and wide area networks, 10 Gigabit Ethernet(10,000 megabits), the fastest Ethernet, is also used (see 10Gigabit Ethernet).

Ethernet


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CONNECTION BITSModems

Modem 56k 53.3 kbit/s

ISDN

64k ISDN 64.0 kbit/s128k dual-channel ISDN 128.0 kbit/s

Wide area networkADSL upstream 64 kbit/s to 1024 kbit/sADSL downstream 256 kbit/s to 8 Mbit/s

Local area networkFast Ethernet (100base-X) 100 Mbit/sGigabit Ethernet (1000base-X) 1 Gbit/s

Bandwidths


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The term protocol is used to refer to a set of rules and

conventions needed for communication betweencommunicating parties.

Computer networks are implemented using the concept oflayered protocols.

A protocol provides a service

For e.g. the post office protocol for reliable parcel transfer servicePeer entities use a protocol to provide a service to a higher-level peer entity

for e.g., truck drivers use a protocol to present post offices with theabstraction of an unreliable parcel transfer service

E.g. OSI Model, TCP/IP ModelProtocols

set of valid messages

meaning of each message

Network Protocol


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application

supporting network applicationsE.g. ftp, smtp, http

transporthost-host data transfer

E.g. tcp, udp packets

networkrouting of datagrams from source todestination

ip, routing protocols

link

data transfer between neighboringnetwork elements

ppp, ethernet

Physicalbits on the wire

TCP/IP

application

transport

network

link

physical


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Bandwidth tells us therate at which data canbe transmitted downthe communicationsline in a given period

of time

Data Communications

FAST BANDWIDTH

SLOW BANDWIDTH


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The higher the bandwidth, the quicker thedata will flow along the lineWeb pages loaded quicker.

Multimedia is downloaded faster.

Internet connection is faster.Less network traffic.

Quicker response time.

Bandwidth


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Also called as PSTN : Public Switched Telephone Network.

Uses traditional telephone system to allow access to theInternet.

Low Bandwidth

Dial Up Connection.

Public Switched Telephone Network.


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Stands for Modulator Demodulator.

First created to take digital signals from a computer andconvert them to analogue so that they can be transmitteddown a telephone line.

Speed at which a modem operates will affect the downloadtime of web pages and files.

Modem

Di i l D C i


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There are a number of connection types

available to us when we want to access theservices from the Internet Each one has adifferent BANDWIDTH.

DSL : Digital subscriber line.

ADSL : Asymmetric DSL.

HSDL : High-speed DSL.

ISDN : Integrated Services Digital Network.

Digital Data Connections

Di i l b ib li


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Also called DSL : Digital subscriber line.

Does not use a modem.

Uses a piece of network equipment similarto a network switch.

More expensiveBandwidth of 128Kbps 256Kbps.

Digital subscriber line

A i Di i l S b ib Li


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Is known as Broadband. or ADSL

Is permanently switched on, no need for dialup.

Has a high bandwidth.

Bandwidths from 100-640Kbps upstreamand from 1.5 to 9 Mbps downstream

Asymmetric Digital Subscriber Line.

Hi h d Di it l S b ib Li


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Is known as HDSL.

Like ADSL, is permanently switched on, noneed for dial up.

Has a higher bandwidth than ADSL.

For businesses purposes768Kbps of symmetric bandwidth

High-speed Digital Subscriber Line.

I t t d S i Di it l N t k


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Is known as ISDN.

Supports Videoconferencing, faxes and voiceapplications.

Users still must dial up.

High speed digital transfer.Integrated services digital network (ISDN)first used DSL protocol suite in 1984

Integrated Services Digital Network.

C bl d


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Connected using broadband coaxial cable thatserves a television.

Upstream bandwidth of 300Kbps to 1 Mbps anddownstream bandwidth of 10Mbps

Cable modems

DSL vs Cable

DSL is a private line with no competing traffic

Cable connections bandwidth change with the userload (number of subscribers using the service)

ProblemsWeb users in rural areas often do not have cableaccess and have limited telephone access (low costvoice-grade lines, rather than data-grade lines)thus bandwidth is limited (


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Large firms with a large amounts of Internet traffic

can lease lines from telecommunication carriersVarious technologies are used; classified by theamount of telephone lines they include:

DS0 (digital signal zero) carries one digital signal

(64Kbps)T1 (or DS1) carries 24 DS0 lines (1.544Mbps)

Fractional T1 (128Kbps and upwards)

T3 (or DS3) carries 30 T1 lines (44.736Mbps)

Connections more expensive than PSTN, ISDN andDSL

Leased-Line Connections

i l k


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Wireless LAN IEEE 802.11a, b, gFixed Point Wireless

Bluetooth

Cellular Telephone Networks.

Wireless Networks

Wi l LAN


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Also called Wireless

Ethernet or Wi-Fi.They follow standard IEEE802.11a, b, gMost common wireless on

LANsBandwidth 11Mbps at 300feetA computer with a Wi-Finetwork can communicatewith a wireless accesspoint (WAP) to become apart of the network

Wireless LAN

Wi l E h Ad


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Wi-Fi devices can roam, i.e. shift from oneWAP to another without user intervention

Increasingly WAPs are becoming available inpublic places, e.g. airports

Wireless Ethernet Advantages

Fi d P i Wi l


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Uses a system ofrepeaters (transmitter-receiver devices) toforward a radio signalfrom the ISP tocustomersUsers antennas areconnected to a devicethat converts radiosignals to Wi-Fipackets which are sentto their computers

Fixed Point Wireless

Bl t th


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One of the first wireless protocols

Operates reliably over 35 feetCan be part of up to 10 networks of eight deviceseach.

When in a networks they are called Personal Area

network or PANBandwidth of 722kbps

Good for wireless printing

Bluetooth

Bl t th Ad t


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Bluetooth technology consumes very littlepower

Bluetooth devices can discover each otherand exchange information automatically

e.g. a user can print to a printer on a networkwithout logging on

Bluetooth Advantages

C ll l T l h N t k


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In 2003, about 500 million mobile (cell) phones

worldwideOriginally slow data communication (10 kbps 384kbps)

Third generation cell phones

Up to 2 MbpsServices Provide

Short message service (SMS) protocol

Web browser which provide web access, email, etc.

Internet access through their cellular networks. Fixed feeplus charge for amount of data transferred

Business potential of mobile commerce

Cellular Telephone Networks

computer networks2003

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