An interconnected collection ofautonomous computers is calledComputer Network. It means twocomputers are said to be interconnectedif they are capable of exchanging theinformation.
Need for NetworkingSharing of Hardware , SoftwareResources and the database.ReliabilityTo enable different computers tocommunicateTo reduce cost of transfer ofdata
Disadvantages of Network Protection from Viruses Central dependency on software and files System becomes more complex and sophisticated
Evolution of Networking 1. ARPANET : This was the firstnetwork which was planted in 1969. Itmeans Advanced Research ProjectsAgency NETwork. Its aim was to connectdifferent computers of differentuniversities and U.S. defense toexchange messages and data. Thisnetwork was expanded very soon by thestudents , scientists , engineers etc. fortheir work. The users were able to sharetheir interests.
2. NSFnet : This was thenetwork which was startedin 1980 by National ScienceFoundation. It was a highcapacity network thanARPANET which was morecapable than ARPANET . Itwas used to do researchwork on the network andsome kind of privatebusiness.
3. INTERNET : It is a worldwidenetwork of Computers network. It wasdeveloped in 1990 by differentcompanies to allow the users to connectone network to the other tocommunicate. It is a super network. Ituses a set of protocols called TCP/IP.4. INTERSPACE : It refers to a visionof what the internet will become infuture. It is a client/server softwareprogram that allows multiple users tocommunicate online with real time audio ,video and text in dynamic 3Denvironment.
Basic TerminologyNodes or ServerWorkstations A Computer The different which facilitatesterminals or the sharing ofcomputers which data , softwareare attached to a and hardwarenetwork and are resources likeable to share the Printer , Modemresources are etc. on thecalled nodes or network is calledworkstations. a Server.
Network Interface UnitIt is an interpreter which isattached to server and all theworkstations to maintain theconnection between them. It isalso called Terminal Access Point(TAP).
TYPES OF NETWORK LOCAL AREA NETWORK (LAN ) METROPOLITAN AREA NETWORK (MAN) WIDE AREA NETWORK (WAN )
LOCAL AREA NETWORK ( LAN ) It is a small computer network that are confined to a localized area like an office , a building etc. Only a definite number of computers can be connected in this network to share the resources . Its range can be up to a few Kilometers.Its main features are• Total diameter not more than 5 km• Data communication at the rate of 100 Mbps• Owned by single organization• Low Error Rates• Provides user access to several resources like printers, Modem etc.
Metropolitan Area Network ( MAN ) This network is larger in size than LAN and it spreads over a city. It means a very large number of computers can be connected in this in a city or from one city to the other. Example : The Cable TV networks which are spread over a city.
WIDE AREA NETWORK ( WAN ) This network spreads across the countries and it is a group of computers that are separated by very large distances. The computers of even one continent can be connected to the other continent. Its main features are :• Spans large geographical area, often a country or continent• Helps in E-Mailing• Data can be received from or sent to remote areas with the help of satellite with less cost
LAN WAN .• Diameter of not more • Span entire countries than a few kms.• Total data rate of at • Data rate less than 1 least several Mbps Mbps• Complete ownership be • Owned by multiple a single organization organizations• Very low error rates • Comparatively higher error rates.
MODEM ( MOdulation/DEModulation ) The device which is used to connect and communicate with computers with the help of telephonic lines . It converts digital data into analog form and vice versa.Working :A modem is a computer peripheral that allows to connect and communicate with the other computers through telephone lines. In MoDem , Mo stands Modulation and Dem stands for Demodulation . Modulation means to convert digital signals to analog signals and Demodulation is reverse of that. The data is transferred form source to the destination through telephone wires and they can only understand analog signals so there is need to convert digital signals to analog . And computer can only understand digital signals . This conversion is done by MoDem.
WORKING OF MODEM Analog signals Analog signalsMODEM MODEM Digital Signals Digital Signals Source Computer Destination (Remote Computer)
Types of MoDem( 1 ) Internal MoDem : TheMoDem which is connected insidethe computer is called InternalMoDem.( 2 ) External MoDem : TheMoDem which is connectedexternally to a computer is calledExternal MoDem.
Network TopologiesThe way of interconnection of the nodes in a network is called theTopology.The different factors on which selection of a topology depends are :( a ) Cost : A Network of computers can reduce the cost to a largeextent.( b ) Reliability : It is more reliable to work in a Computer Network .Hence if a node fails to work the data can be achieved from someother nodes.( c ) Flexibility : The topology should allow for easy reconfigurationof the network.The different topologies are :
Star Topology It is consisted of a central node to which all other nodes are connected by a single path. Its different advantages and disadvantages are :Advantages :( 1 ) One Device per connection : In this topology failure of a single connection typically involves disconnecting one node from an otherwise fully functional network.( 2 ) Simple Access protocols : In this access protocols are very simple.Disadvantages :( 1 ) Long Cable Length : This topology uses a very long cable as each node id directly connected to the centre.( 2 ) Central Dependency : If the central node fails , the entire network stops working.
Bus or Linear Topology It is consisted of a single length of the transmission medium onto which the various nodes are attached . Its different advantages and disadvantages are :Advantages :( 1 ) Short Cable Length : There is a single common data path connecting all nodes , so this topology uses a very short cable .( 2 ) Easy to Expand : In this topology additional nodes can be connected at any point along its length.Disadvantages :( 1 ) Fault detection : In this topology it is very difficult to detect a faulty node .( 2 ) Nodes must be intelligent : All the nodes working in this topology must be intelligent.
Ring or Circular Topology In this each node is connected to two and only two neighbouring nodes. Data is transmitted from one to another node and is transmitted onwards to another. In this topology the data travels only in one direction. Its different advantages and disadvantages are :Advantages :( 1 ) Short Cable Length : There is very short cable which is used to develop a Computer Network( 2 ) Suitable for optical fibers : In this topology for very fast speed transmission optical fibers can be used.Disadvantages :( 1 ) Node Failure causes network failure : In this topology if one node fails to pass the data through itself , the entire network fails.( 2 ) Network reconfiguration is difficult : It is not possible to shut down a small section of the ring .
Tree Topology A variation of bus topology is the tree topology. The shape of the network is just like an inverted tree with the central root branching and sub-branching to the extremities of the network.Advantages :( 1 ) Easy to Expand : It is very easy expand this topology . It means nodes can be connected easily.( 2 ) Fault isolation is easy : It is easy to find the faulty node in this topology.Disadvantages :( 1 ) Dependency on root computer : The total dependence is on the root computer . If it fails to work , the entire network will stop working.( 2 ) Complex Access Protocols : The protocols designed for this topology are generally very complex.
Backbone Network • A backbone is a central interconnecting structure which is used to connect two or more networks e.g. LANs together to form a WANe.g. FDDI – Fiber Distributed Data Interface
REPEATER A repeater is a device that amplifiesa signal being transmitted on anetwork for long distances. It is used in long network lines, whichexceed the maximum rated distancefor a single run.
BridgeA bridge is used to connecttwo LANs which are physicallyseparated but logically same i.e. following the same topology.
Router It is a device that links twonetworks which can handledifferent protocols. The routersuse physical addresses. Itimproves the performance of thenetwork.
GatewayA gateway is a device that connectsdissimilar networks. It gives an intelligentconnection between a local network andan external network with differentstructures . It is a special device which allowsdifferent networks to talk to internet thatuses TCP/IP.
The 80-20 Rule80 percent of the traffic on a given network segment islocal and 20 percent of the network traffic should needto move across a backbone networks (sub-network.)How to Improve Performance of a LAN ?1.Moving resources ( files etc. ) from one server toanother server to contain traffic locally within aworkgroup.2.Moving users logically within a workgroup.3.Adding servers to access them locally withoutcrossing the backbone networks.
Network SecurityThe different Prevention methods are used while working in Networkenvironment for security.( 1 ) Authorization : It determines whether the ISP has granted theaccess to the web service or not. It is done by asking the user legallogin-Id.( 2 ) Authentication : It is a way to check the password protection ofan authorised user.( 3 ) Firewall : It is a system designed to prevent the unauthorisedusers to access to or from a private network. In this we can alsoencrypt the data.( 4 ) Encrypted Smart cards : It is smart hand-held card that cangenerate a token that a computer can recognise. Every time a newtoken is generated.( 5 ) Biometric System : It includes some unique aspect of a person’sbody such as finger prints etc. To establish his identity.