INTRODUCTION TO ICT.

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1 INTRODUCTION TO ICT. (Introducing Basic Network Concepts) Lecture # By: M.Nadeem Akhtar. Department of CS & IT. URL: 1

2 INTRODUCTION TO NETWORKS A network consists of two or more entities or objects sharing resources and information. A computer network consists of two or more computing devices connected to each other to share resources and information. The network becomes a powerful tool when computers communicate and share resources with other computers on the same network or entirely distinct networks. Computers on a network can act as a client or a server. A client is a computer that requests for resources. A server is a computer that controls and provides access to resources. 2

3 COMPUTER NETWORK Multiple computers that are connected together to share information and other resources. Computer Networks = Computers + Communications Examples of Computer Network Usage: I can send an message to a remote computer using the SMTP protocol I can browse documents residing on a remote computer using the HTTP protocol I can download or upload files to a remote computer using the FTP protocol I can run a program on a remote computer using the TELNET protocol 3

4 Computer A Computer E Example of a Computer Network Hub Computer D Computer B Computer C 4

5 COMPONENTS OF CONVENTIONAL COMPUTER NETWORKS 1. Computers 2. Network Interface Cards (NIC) 3. Hub 4. Cables I/O device that plugs into the computer Enables it to communicate over a network The network traffic controller Are either electrical or optical Not required at all for wireless networks 5. Protocol Rules governing communications over the network 5

6 HOW DOES A CONVENTIONAL NETWORK WORK? 1. Suppose computer A wants to send a message to D 2. Computer A sends the message to its NIC 3. The NIC translates the message into electrical pulses suitable for the computer network in use & transmits it to the hub through the cable 4. The hub receives them andforwards them to all computers connected to the it 5. The NICs of all computers connected to the hub receive the forwarded electrical pulses 6. The NIC of computer D decides that the message is for it, & translates the pulses back to a form suitable for the computer 6

7 HUB A device that is used to connect several computers to form a network A hub has several ports. The number generally is 8, 12, 16, 24, 32, or 48 Each computer in a network is connected to one of those ports through a cable A computer wanting to send a message to one of the others in the network sends a message to the hub, which, in turn, broadcasts the message to all others connected to it 7

8 PACKET The smallest unit of data transmitted over a computer network A message to be transferred over the network is broken up into small packets by the sending computer Each packet contains the following info: Sender's address Destination address Data Error-recovery info All packets travel independently When all packets are received by the destination computer, it reassembles them to form the original message 8

9 CLASSIFICATION OF NETWORKS Classification by network geography. Classification by component roles. 9

10 CLASSIFICATION BY NETWORK GEOGRAPHY Networks are frequently classified according to the geographical boundaries spanned by the network itself. LAN, WAN, and MAN are the basic types of classification, of which LAN and WAN are frequently used. 10

11 CLASSIFICATION BY NETWORK GEOGRAPHY Local area network (LAN): A LAN covers a relatively small area such as a classroom, school, or a single building. LANs are inexpensive to install and also provide higher speeds. 11

12 CLASSIFICATION BY NETWORK GEOGRAPHY Local area network 12

13 CLASSIFICATION BY NETWORK GEOGRAPHY Metropolitan area network (MAN): A MAN spans the distance of a typical metropolitan city. The cost of installation and operation is higher. MANs use high-speed connections such as fiber optics to achieve higher speeds. 13

14 CLASSIFICATION BY NETWORK GEOGRAPHY Metropolitan area network 14

15 CLASSIFICATION BY NETWORK GEOGRAPHY Wide area network (WAN): WANs span a larger area than a single city. These use long distance telecommunication networks for connection, thereby increasing the cost. The Internet is a good example of a WAN. 15

16 CLASSIFICATION BY NETWORK GEOGRAPHY Wide area network 16

17 CLASSIFICATION BY COMPONENT ROLES Networks can also be classified according to the roles that the networked computers play in the network s operation. Peer-to-peer, server-based, and client-based are the types of roles into which networks are classified. 17

18 CLASSIFICATION BY COMPONENT ROLES Peer-to-peer: In a peer-to-peer network, all computers are considered equal. Each computer controls its own information and is capable of functioning as either a client or a server depending upon the requirement. Peer-to-peer networks are inexpensive and easy to install. They are popular as home networks and for use in small companies. Most operating systems come with built-in peer-to-peer networking capability. The maximum number of peers that can operate on a peer-to-peer network is ten. Each peer shares resources and allows others open access to them. 18

19 CLASSIFICATION BY COMPONENT ROLES Peer-to-peer (continued): Peer-to-peer networks become difficult to manage when more security is added to resources, since the users control their security by password-protecting shares. Shares can be document folders, printers, peripherals, and any other resource that they control on their computers. 19

20 CLASSIFICATION BY COMPONENT ROLES Peer-to-peer network 20

21 21

22 CLASSIFICATION BY COMPONENT ROLES 2-Server-based: A server-based network offers centralized control and is designed for secure operations. In a server-based network, a dedicated server controls the network. A dedicated server is one that services the network by storing data, applications, resources, and also provides access to resources required by the client. These servers can also control the network s security from one centralized location or share it with other specially configured servers. 22

23 CLASSIFICATION BY COMPONENT ROLES Server-based network 23

24 CLASSIFICATION BY COMPONENT ROLES Client-based: Client-based network servers process requests from clients and return just the results. These networks take advantage of the powerful processing capabilities of both the client and the server. Application servers and communications servers are examples of client-based networks. 24

25 CLASSIFICATION BY COMPONENT ROLES Client-based network 25

26 CONNECTING LANS TO OTHER NETWORKS Special-purpose devices are used to link LANs to other networks They may belong to one of the following categories: Routers Bridges Gateways Modems 26

27 ROUTER A special-purpose device that directs data traffic when several paths are available A router examines the destination info in each arriving packet and then routes it through the most efficient path available The router either delivers the packet to the destination computer across a local network or forwards the packet to another router that is closer to the final destination by using Router Information Protocol. 27

28 Type A header Payload Type A header SERVER Payload ROUTER Significant geographical distance ROUTER SERVER Type A header Payload LAN 1 LAN 2 28 WAN

29 BRIDGE Used to form a connection between two separate, but similar networks In a way, it creates an extended LAN by passing information between two or more LANs 29

30 GATEWAY A special-purpose computer that connects and translates betweennetworks that usedifferent communications protocols LAN s may use a gateway (or router) to connect to the Internet 30

31 A gateway performs the translation between two different types of networks

32 MODEM I/O device used for connecting two computers over telephone lines modem = modulator + demodulator Modulator converts computer messages to electrical pulses that are suitable for transmission over the telephone lines Demodulator converts electrical pulses received over telephone lines into messages that are comprehensible for computers 32

33 NETWORK TOPOLOGIES The pattern in which computers are connected to form a network Popular patterns: Star Bus Ring Networks are also formed by combining 2 or more of these 4 basic patterns 33

34 Computer D STAR Computer A Server Computer C Computer B 34

35 STAR A computer sends the address of the intended receiver and the data to the server The server then sends the message to the intended receiver This topology allows multiple messages to be sent simultaneously Costly, because it uses an additional computer to direct the data Costly, because each node is individually wired to the server If the server goes down, so does the network If any of the nodes goes down, the rest of the network is not affected 35

36 Computer A Computer C BUS Bus: A high speed cable Computer B Computer D 36

37 BUS No server is required One computer sends data to another by broadcasting the address of the receiver and the data over the bus All the computers in the network look at the address simultaneously, and the intended recipient accepts the data A bus network, unlike ring or star networks, allows data to be sent directly from one computer to another However, only one computer at a time can transmit data. The others must wait to until the bus gets idle If any of the nodes goes down, the rest of the network is not affected 37

38 Computer D RING Computer A Computer C Computer B 38

39 RING No server is required A computer sends the message to itsneighbor. Theneighbor examines the message to determine if it is the intended recipient If the data are not intended for that particular neighbor, itpasses the message to the next computer in the ring. This process is repeated until the data arrive at their intended recipient This topology allows multiple messages to be carried, simultaneously Data transmission is slow since each message is checked by each computer New nodes are difficult to add Messages propagate in one direction only The network fails if a single node fails 39

40 Computer A COMBINATION Computer B Hub Computer D Computer C Hub Computer E 40 Computer F

41 NETWORKING PROTOCOLS Networks use protocols, or rules, to exchange info through shared channels Protocolsprevent collisions of packets caused bysimultaneous transmission between two or more computers Several protocols are available for various types of networks. Here we discuss two that are popular for LANs: 1. Ethernet. 2. Token Ring. 41

42 1-ETHERNET PROTOCOL A computer using this protocol checks if a sharedconnection is in use before transmitting a message If not, the computer transmits data Two computers may sense an idle connection and may send packets simultaneously. To account for such situations, transmitting computers continue to monitor the connection and re-transmit if a packet collision occurs 42

43 2-TOKEN RING PROTOCOL This protocol passes a special message called atoken through the network A computer that receives the token is given permission to send a packet of information If the computer has no packet to send, it passes the token to the next computer 43

44 TYPES OF COMMUNICATION CHANNELS 1. Wire 2. Wireless A key characteristic of these channels is bandwidth. 44

45 DATA RATE Capacity of a communication channel for carrying data. Measured in bits/s (bps), Kb/s, Mb/s, Gb/s, Tb/s Optical fiber channels have the highest (1 Tb/s) Telephone lines the lowest (56 kb/s) A normal telephone wire has a very low bandwidth so it is not possible to transmit many data. The higher the data ratethe greater the amount of data can be transmitted. 45

46 TYPES OF COMMUNICATION CHANNELS Wire Copper Twisted-pair Coaxial cable Optical fiber Wireless Line-of-sight Microwave Optical Non-line-of-sight Satellite Radio Cellular 46

47 TYPES OF COMPUTER NETWORKS ACCORDING TO THE NETWORK ACCESS POLICY Private Public 47

48 PRIVATE NETWORKS Organizations having many computers usually connect them in the form of private networks Access to these network is restricted to authorized computers only. This allows computers from within the organization to exchange info, but keeps the info private and protected from outsiders All equipment on a private network is generally for the exclusive use of that organization 48

49 PUBLIC NETWORKS All networks that are not private, are public Example: Internet Communication equipment used in these networks is generally being used by users belonging to several (possibly thousands of) organizations as well as those belonging to no organization. 49

50 VIRTUAL PRIVATE NETWORK Suppose that a client sitting at a local branch network of a company wants to be part of head office network of the company. A VPN provides another option of remote access. It is defined as a secure, dedicated point to point connection over the internet. In VPN, we use internet infrastructure for connection instead of a special telephone line. VPN tunnel are managed by Point to Point Tunneling Protocol (PPTP) which due to encryption provides secure transport of private communication over the internet. VPN is a cost saving measure as compared to simple remote access using dial up connection. 50

51 NETWORK SECURITY Keeping an eye on the security ofprivate networks (e.g. LANs) is relatively easy However, their connections to other networks (e.g. the Internet) pose a security risk because the one has no control over users on those networks. Applications transferred from the Internet to the LAN may contain computer viruses External, unauthorized users may gain access to sensitive data A special type of gateway - a firewall can keep external users from accessing resources on the LAN while letting LAN users access the external info 51

52 FIREWALL A system that that guards a private network, enforcing an access/deny policy to all traffic going to and coming from the Internet It keeps an eye on all the packets that go in and out of the private network and blocks them or allows them to continue to their destination according to the policy. Firewall Policy: Example One can configure a firewall to allow only to enter the private network, thus shielding it from any malicious attacks except for those via . 52

53 Internet Firewall Private Network 53

Chapter Topics Part 1. Network Definitions. Behind the Scenes: Networking and Security

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