Computer network


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Computer network

  1. 1. AIM: TO STUDY THE BASICS OF COMPUTER NETWORKWhat is computer network:• A computer network, often simply referred to as a network, is a collection ofhardware components and computers interconnected by communication channelsthat allow sharing of resources and information.• Where at least one process in one device is able to send/receive data to/from atleast one process residing in a remote device, then the two devices are said to bein a network.Why networking:• Information access.• Sharing of Resources.• Facilitate Communication.• Interactive entertainment.• High reliability.• Saving money.What a network includes:• Transmission Hardware (NIC, MODEM, other transmitter)• Intermediate hardware devices(Hub, Repeaters, Amplifiers, Switch, Router)
  2. 2. • Protocol softwareWhat a network does:• Provides communication that is1. Reliable2. Fair3. Efficient• Automatically detects and corrects1. Data corruption and data loss2. Duplication3. Out of order delivery• Automatically finds optimal path from source to destinationLink:Link is defined as the physical transmission medium that connects networkeddevices/systemsDifferent types of links:• Point-to-Point or Direct Access Link1. Such links provide a direct path between two devices,thus forming a networkthat does not have intermediate devices.2. Can not be used to connect large networks.• Multiple Access Link1. When multiple devices are connected to one another via a single link, suchthateach of the devices is connected by the link to all other devices at thesame time,the link is said to be a multiple-access link.2. The main channel that connects all thedevices is also called as a ‘bus’ or anether
  3. 3. AIM: TO STUDY THE TYPES OF NETWORKSTypes of network are:• MAN(Metropolitan Area Network)• LAN (Local Area Network)• WAN(Wide Area Network)LANFeatures• A group of computers that share a common connection and are usually in a smallarea or even in the same building form a LAN.• They are usually connected by lan cables and have high speed connections.• Security & Administration: A LAN administrator is one who supervises theoperation of a LAN. He takes care of tasks like adding or deleting users, creatingpasswords providing authorizations and other resources like printers and backing updata.• Range of LAN-90mts best but we can go upto 150 also.ADVANTAGES:• Reliability & Stability: LANS tend to be very reliable failures on a LAN are mostlydue to wrong or improper installation and monitoring. Software that comes alongwith a LAN provides a number of useful programs like error-detection, preventionof transmission loss and excellent security features.
  4. 4. • Files can be backed up more easily when they are all on a central fileserver ratherthan when they are scattered across a number of independent workstations.• Networks also allow security to be established, ensuring that the network usersmay only have access to certain files and applications.• Software and resources can be centrally managed.DISADVANTAGES:• Special security measures are needed to stop users from using programs and datathat they should not have access to.• Networks are difficult to set up and need to be maintained by skilled technicians.• If the file server develops a serious fault, all the users are affected, rather thanjust one user in the case of a stand-alone machine.• Limited no. of users.: Most LAN supports number of users usually around five orten. More users can be supported by connecting different LANs together, whichgives better results than making one; by network of the nature of MAN.MANFeatures:• This is a larger network that connects computer users in a particular geographicarea or region.
  5. 5. • The MAN network usually exist to provide connectivity to local ISPs, cable tv, orlarge corporations.• Range of Man: can connect cities 10 kms - 50kms• It is far larger than a LAN and smaller than a WAN.• The network size falls intermediate between LANs and WANs. A MAN typicallycovers an area of between 5 and 50 km diameter. Many MANs cover an area thesize of a city, although in some cases MANs may be as small as a group of buildings.ADVANTAGES• It provides a good back bone for a large network and provides greater access toWans.• A MAN would probably be the next fastest as the data is only travelling around thecity.DISADVANTAGES:• more cable required for a man connection from one place to another.• The large the network becomes difficult to mange.• It is difficult to make the system secure from hackers and industrial espionage.WANFEATURES:• This is the largest network and can interconnect networks throughout the worldand is not restricted to a geographical location.• Most WANs exist to connect LANs that are not in the same geographical area.• This technology is high speed and very expensive to setup.• Covers a Large geographical area.
  6. 6. ADVANTAGES:• Covers a large geographical area so long distance businesses can connect on the onenetwork• Shares software and resources with connecting workstations• Messages can be sent very quickly to anyone else on the network. These messagescan have pictures, sounds, or data included with them (called attachments).• Everyone on the network can use the same data. This avoids problems where someusers may have older information than others.• large network cover.DISADVANTAGES:• Are expensive and generally slow• Need a good firewall to restrict outsiders from entering and disrupting thenetwork• Information may not meet local needs or interests• Vulnerable to hackers or other outside threats
  7. 7. AIM: TO STUDY THE TYPES OF NETWORK TOPOLOGY.Two or more computers connected together through communication media form acomputer network. The arrangement of computers in a network is called NetworkTopology. It is a physical layout of connected computer.Types of topologies are:-• STAR TOPOLOGY• BUS TOPOLOGY• RING TOPOLOGY• TREE TOPOLOGY• MESH TOPOLOGYSTAR TOPOLOGY:This topology consists of a central node to which all other nodes are connected by a singlepath.ADVANTAGES:• EASE OF SERVICE: The star topology has a number of concentration points. Theseprovide easy access for service or reconfiguration of the network.• ONE DEVICE PER CONNECTION: Connection points in any network are inherentlyprone to failure. In the star topology, failure of a single connection typicallyinvolves disconnecting one node from an otherwise fully functional node.
  8. 8. • CENTRALIZED CONTROL: The fact that the centralized node is connecteddirectly to every other node in he network means that faults are easily detectedand isolated. It is a simple matter to disconnect failing nodes from the system.• SIMPLE ACCESS PROTOCOLS: Any given connection in a star topology involves onlythe central node, In this situation, connection for who has control of the mediumfor the transmission purposes is easily solved. Thus in a star network, accessprotocols are very simple.DISADVANTAGES:• LONG CABLE LENGTH: Because each node is directly connected to the centre, thestar topology necessitates a large number quantity of cable.• DIFFICULT TO EXPAND: The addition of a new node to star network involves aconnection all the way to the central node.• CENTRAL NODE DEPENDENCY: If the central node faiuls, the entire network isrendered inoperable.BUS TOPOLOGY:In the bus topology, the computers are connected through a common communication media.A special type of central wire is used as communication media. This central wire is calledBus. The computer are attached through the bus the ends of the bus are closed with theterminator .The terminators are used to absorb signals.ADVANTAGES:
  9. 9. • SHORT CABLE LENGTH AND SIMPLE WIRING LAYOUT: Because there is a singlecommon data path connecting nodes, the linear topology allows a very short cablelength to be used.• INEXPENSIVE.• EASY TO EXTEND: Additional nodes can be added to the network at any point.DISADVANTAGES:• Fault diagnosis is difficult.• Performance decreases.• Weak signals.RING TOPOLOGY:In ring topology each computer is connected to the next computer and the last computer isconnected to the first computer. Data is accepted from one of the neighboring nodes andis transmitted onwards to another. Thus data travels only in one direction only, from nodeto node around the ring.ADVANTAGES:• Short cable length.
  10. 10. • It provides an orderly network in which every device has access to the token andcan transmit.• Suitable for optical fibres.DISADVANTAGES:• Node failure causes network failure.• Difficult to diagnose faults.• Change mode with adding or removing a device effect the entire network.TREE TOPOLOGY:Tree topologies integrate multiple star topologies together onto a bus. In its simplestform, only hub devices connect directly to the tree bus, and each hub functions as the"root" of a tree of devices. This bus/star hybrid approach supports future expandabilityof the network much better than a bus (limited in the number of devices due to thebroadcast traffic it generates) or a star (limited by the number of hub connection points)alone.ADVANTAGES:• Point-to-point wiring for individual segments.• Supported by several hardware and software venders
  11. 11. DISADVANTAGES:• Overall length of each segment is limited by the type of cabling used.• If the backbone line breaks, the entire segment goes down.• More difficult to configure and wire than other topologies.MESH TOPOLOGY:A mesh network or mesh topology uses separate cable to connect each device to everyother device on the network, providing a straight communication path .ADVANTAGES:• Enhance for error tolerance provided by redundant links.• Easy to troubleshoot.DISADVANTAGES:• Difficult to install and maintain.• Expensive.• Large cable length.
  12. 12. AIM: TO STUDY THE TYPES OF TRANSMISSION MEDIA.The means through which data is transformed from one place to another is calledtransmission or communication media. There are two categories of transmission media usedin computer communications:• BOUNDED/GUIDED MEDIA• UNBOUNDED/UNGUIDED MEDIAGUIDED MEDIA• Bounded media are the physical links through which signals are confined to narrowpath. These are also called guided media.• Bounded media are made up to a external conductor (Usually Copper) bounded byjacket material.• Bounded media are great for LABS because they offer high speed, good securityand low cast. However, some time they cannot be used due distance communication.Three common types of bounded media are used of the data transmission. Theseare:1. Coaxial Cable2. Twisted Pairs Cable3. Fiber Optics CableCOAXIAL CABLES:
  13. 13. Coaxial cable is very common & widely used commutation media. For example TV wire isusually coaxial. Coaxial cable gets its name because it contains two conductors that areparallel to each other. The center conductor in the cable is usually copper. The copper canbe either a solid wire or stranded martial. Outside this central Conductor is a non-conductive material. It is usually white, plastic material used to separate the innerConductor form the outer Conductor. The other Conductor is a fine mesh made fromCopper. It is used to help shield the cable form EMI. Outside the copper mesh is the finalprotective cover.CHARACTERISTICS:• Low cost• Easy to install• Up to 10Mbps capacity• Medium of attenuationADVANTAGES:• Inexpensive• Easy to wire• Easy to expand• Moderate level of EMI immunityDISADVANTAGES:• Single cable failure can take down an entire network.TWISTED PAIR CABLE:The most popular network cabling is Twisted pair. It is light weight, easy to install,inexpensive and support many different types of network. It also supports the speedof 100 mbps. Twisted pair cabling is made of pairs of solid or stranded copper twistedalong each other. The twists are done to reduce vulnerably to EMI and cross talk. Thenumber of pairs in the cable depends on the type. There are two types of twisted pairscabling:• Unshielded twisted pair (UTP)• Shielded twisted pair (STP)UNSHIELDED TWISTED PAIR (UTP):UTP is more common. It can be either voice grade or data grade depending on thecondition. UTP cable normally has an impedance of 100 ohm. UTP cost less than STP andeasily available due to its many use. There are five levels of data cabling.
  14. 14. TYPE DESCRIPTIONCAT1 Voice-grade transmission only; No data transmission.CAT2 Data grade transmission up to 4 mbps.CAT3 Data grade transmission up to 10 mbps.CAT4 Data grade transmission up to 16 mbps.CAT5 Data grade transmission up to 1000 mbps.CHARACTERISTICS:• low cost• easy to install• High speed capacity• High attenuation• Effective to EMI• 100 meter limitADVANTAGES:• Easy installation• Capable of high speed for LAN• Low costDISADVANTAGES:• Short distance due to attenuation.SHIELDED TWISTED PAIR (STP):
  15. 15. It is similar to UTP but has a mesh shielding that’s protects it from EMI which allows forhigher transmission rate.CHARACTERISTICS:• Medium cost• Easy to install• Higher capacity than UTP• Higher attenuation, but same as UTP• Medium immunity from EMI• 100 meter limitADVANTAGES:• Shielded• Faster than UTP and coaxialDISADVANTAGES:• More expensive than UTP and coaxial• More difficult installation• High attenuation rateFiber Optics:Fiber optic cable uses electrical signals to transmit data. It uses light. In fiber optic cablelight only moves in one direction for two way communication to take place a secondconnection must be made between the two devices. The fibre cable consists of threepieces:• The Core i.e the glass or plastic through which light travels.• The Cladding which is the covering of the core that reflects light back to the core.
  16. 16. • The Protective covering, which protects the fibre cable from hostile environment.CHARACTERISTICS:• Expensive• Very hard to install• Capable of extremely high speed• Extremely low attenuation• No EMI interferenceADVANTAGES:• Fast• Low attenuation• No EMI interferenceDISADVANTAGES:• Very costly• Hard to installCOMPARISON TABLE OF GUIDED MEDIA:TYPE SUBTYPE MAX.SEGMENTLENGTHBANDWIDTHSUPPLIEDINSTALLATION COST INTERFERENCETWISTEDPAIRCABLEUTP 100 MTS 100 Mbps Easy Cheapest HighSTP 100 MTS 500 Mbps Moderate Moderate ModerateCOAXIALCABLETHINNET 185 MTS 10 Mbps Easy Cheap ModerateTHICKNET 500 MTS 100 Mbps Hard Moderate LowFIBREOPTICCABLEMULTINODE 2 KMS 100 Mbps Very Hard Expensive NoneSINGLENODE 100KMS 2 Gbps Very Hard Expensive NoneUNGUIDED MEDIA:Unguided media relates to data transmission through the air and is commonly referred toas wireless. The transmission and reception of data is carried out using antenna.
  17. 17. RADIO WAVES:Radio transmission works with or without line of sight. If line of sight is possible thentransmission can take place between sending antenna and receiving antenna. The placementof antenna has to take into account the curvature of the Earth with antenna being builttaller accordingly. This will also allow for greater transmission distances. If line of sightcannot be implemented then signals can be broadcast to the upper layers or theatmosphere or space and then transmitted back to Earth.ADVANTAGES:• Radio wave transmission offers mobility.• It provides cheaper than digging trenches for laying cables and maintainingrepeaters and cables if cables get broken by a variety of causes.• It offers freedom from land acquisition rights that are required for laying,repairing the cables.DISADVANTAGES:• It is an insecure communication.• Radio wave propagation is susceptible to weather effects like rains, thunder stormsetc.MICRO WAVES:In microwave communication, parabolic antennas are mounted on towers to send a beam toother antennas tens of kilometers away. The higher the tower, the greater the range.With a 100-meter high tower, distances of 100 km between tower are feasible. It is a lineof sight transmission.
  18. 18. ADVANTAGES:• No cables needed• Multiple channels available.• Have the ability to communicate over oceans.• Wide bandwidthDISADVANTAGES:• Line-of-sight will be disrupted if any obstacle, such as new buildings, are in the way• Signal absorption by the atmosphere. Microwaves suffer from attenuation due toatmospheric conditions.• Towers are expensive to build.SATELLITE:In satellite communication the earth station consists of a satellite dish that functions asan antennae and communication equipment to transmit and receive data from satellitespassing overhead.
  19. 19. ADVANTAGES:• High bandwidth• Coverage over a large geographical area• Can be cheaper over long distancesDISADVANTAGES:• Huge initial cost• Noise and interference• Propagation delay
  20. 20. AIM: TO STUDY TCP/IP PROTOCOLS.TCP/IP is based on a four-layer reference model. All protocols that belong to the TCP/IPprotocol suite are located in the top three layers of this model. As shown in the aboveillustration, each layer of the TCP/IP model corresponds to one or more layers of theseven-layer Open Systems Interconnection (OSI) reference model proposed by theInternational Standards Organization (ISO).LAYER DESCRIPTION PROTOCOLSAPPLICATION Defines TCP/IP application protocols and how hostprograms interface with transport layer services touse the network.HTTP, Telnet,FTP, TFTP,SNMP, DNS,SMTP,TRANSPORT Provides communication session management betweenhost computers. Defines the level of service andstatus of the connection used when transporting data.TCP, UDP,RTPINTERNET Packages data into IP datagram’s, which containsource and destination address information that isused to forward the datagrams between hosts andacross networks. Performs routing of IP datagrams.IP, ICMP,ARP, RARPNETWORK INTERFACE Specifies details of how data is physically sentthrough the network, including how bits areelectrically signaled by hardware devices thatinterface directly with a network medium, such ascoaxial cable, optical fiber, or twisted-pair copperwire.Ethernet,Token Ring,FDDI, X.25,Frame Relay,RS-232, v.35
  21. 21. AIM: TO STUDY INNER WORKING OF AN E-MAIL.IntroductionE-mail (electronic mail) is the exchange of computer-stored messages bytelecommunication. E-mail messages are usually encoded in ASCII text. However, you canalso send non-text files, such as graphic images and sound files, as attachments sent inbinary streams. E-mail is one of the protocols included with the Transport ControlProtocol/Internet Protocol (TCP/IP) suite of protocols. A popular protocol for sending e-mail is Simple Mail Transfer Protocol and a popular protocol for receiving it is POP3. BothNetscape and Microsoft include an e-mail utility with their Web browsers.HOW EMAIL WORKS:EMAIL CLIENTS:Many people use well-known stand-alone clients like MicrosoftOutlook, Outlook Express, Eudora or Pegasus. People who subscribe to free e-mail serviceslikeHotmail or Yahoo uses an e-mail client that appears in a Web Page. No matter which typeOf client you are using, it generally does four things:• It shows you a list of all of the messages in your mailbox by displaying the messageheaders. The header shows you who sent the mail, the subject of the mail and mayalso show the time and date of the message and the message size.• It lets you select a message header and read the body of the e-mail message.• It lets you create new messages and send them. You type in the e-mail address ofthe recipient and the subject for the message, and then type the body of themessage.• Most e-mail clients also let you add attachments to messages you send and save theattachments from messages you receive.For the vast majority of people right now, the real e-mail system consists of twodifferentservers running on a server machine. One is called the SMTP server, where SMTPstands for Simple Mail Transfer Protocol. The SMTP server handles outgoing mail. Theother is either a POP3 server or an IMAP server, both of which handle incoming mail. POPstands for Post Office Protocol, and IMAP stands for Internet Mail Access Protocol. TheSMTP server listens on well-known port number 25, POP3 listens on port 110 and IMAPUses port 143.
  22. 22. SMTP ServerWhenever you send a piece of e-mail, your e-mail client interacts with the SMTP server tohandle the sending. The SMTP server on your host may have conversations with otherSMTP servers to actually deliver the e-mail. The SMTP server takes the "to" address( and breaks it into two parts:• The recipient name (suresh)• The domain name ( the "to" address had been another user at, the SMTP server would simplyhand the message to the POP3 server for (using a little program called theDelivery agent). Since the recipient is at another domain, SMTP needs to communicatewith that domain.The SMTP server has a conversation with a Domain Name Server, or DNS. It says, "Canyou give me the IP address of the SMTP server for" The DNS replieswith the one or more IP addresses for the SMTP server(s) that Daybegins operates.The SMTP server at connects with the SMTP server at Daybegins using port25. It has the same simple text conversation that my e-mail client had with the SMTPserver for Xserves, and gives the message to the Daybegins server. The Daybegins serverrecognizes that the domain name for suresh is at Daybegins, so it hands the message toDaybeginss POP3 server, which puts the message in sureshs mailbox.If, for some reason, the SMTP server at Xserves cannot connect with the SMTP server atDaybegins, then the message goes into a queue. The SMTP server on most machines uses aprogram called send mail to do the actual sending, so this queue is called the send mailqueue. Send mail will periodically try to resend the messages in its queue. For example, itmight retry every 15 minutes. After four hours, it will usually send you a piece of mail thattells you there is some sort of problem. After five days, most send mail configurations giveup and return the mail to you undelivered.
  23. 23. POP3 ServerIn the simplest implementations of POP3, the server really does maintain a collection oftext files-- one for each e-mail account. When a message arrives, the POP3 server simply appends itto the bottom of the recipients file!When you check your e-mail, your e-mail client connects to the POP3 server using port110. The POP3 server requires an account name and a password. Once you have loggedin, the POP3 server opens your text file and allows you to access it.IMAP ServerAs you can see, the POP3 protocol is very simple. It allows you to have a collection ofmessages stored in a text file on the server. Your e-mail client (e.g. Outlook Express) canconnect to your POP3 e-mail server and download the messages from the POP3 text fileonto your PC. That is about all that you can do with POP3.Many users want to do far more than that with their e-mail, and they want their e-mail toremain on the server. The main reason for keeping your e-mail on the server is to allowusers to connect from a variety of machines. With POP3, once you download your e-mail itis stuck on the machine to which you downloaded it. If you want to read your e-mail bothon your desktop machine and your laptop (depending on whether you are working in theoffice or on the road), POP3 makes life difficult. IMAP (Internet Mail Access Protocol) isa more advanced protocol that solves these problems. With IMAP, your mail stays on thee-mail server. You can organize your mail into folders, and all the folders live on the serveras well. When you search your e-mail, the search occurs on the server machine, ratherthan on your machine. This approach makes it extremely easy for you to access your e-mailfrom any machine, and regardless of which machine you use, you have access to all of yourmail in all of your folders. Your e-mail client connects to the IMAP server using port 143.The e-mail client then issues a set of text commands that allow it to do things like list allthe folders on the server, list all the message headers in a folder, get a specific e-mailmessage from the server, delete messages on the server or search through all of the e-mails on the server.One problem that can arise with IMAP involves this simple question: “If all of my e-mail isstored on the server, then how can I read my mail if I am not connected to the Internet?”To solve this problem, most e-mail clients have some way to cache e-mail on the localmachine.For example, the client will download all the messages and store their complete contentson the local machine (just like it would if it were talking to a POP3 server). The messagesstill exist on the IMAP server, but you now have copies on your machine. This allows you toread and reply to e-mail even if you have no connection to the Internet. The next time youestablish a connection, you download all the new messages you received while disconnectedand send all the mail that you wrote while disconnected.