Computer networks

1. Computer networks Lecture#6 Date:

2. Computer Network • Any system of interconnected computers, computer peripheral equipments used for transmit and receive of information.

3. Applications of Networks • Resource Sharing • Hardware (computing resources, disks, printers) • Software (application software) • Information Sharing • Easy accessibility from anywhere (files, databases) • Search Capability (WWW) • Communication • Email • Message broadcasting

4. Components of a Computer Network

5. Components of a Network A computer network typically includes four things: • Network interface cards (NICs) • Networking Software • Networking Media • Networking Devices

6. 1) Network interface cards (NICs): • Plugs into the back of your computers and lets them send and receive messages from other computers • The MAC address is a 48 bit long unique value associated with a network adapter. • MACaddresses are also known as hardware addresses or physical addresses.

7. IP Address • Every machine on the Internet­ has a unique identifying number, called an IP Address. • A typical IP address looks like this: 216.27.61.137 • Computers communicate in binary form. Look at the same IP address in binary: 11011000.00011011.00111101.10001001

8. 2) Networking Software TCP/IP • The basic communication language or protocol of the Internet. • The TCP/IP model has four layers. • Each layer performs a certain role or task. • Each layer a packet of information travels through adds what is called a header.

9. TCP/IP Data Communication Example E-mail message Data Data Segment Header Segment Data Network Header Segment Header Packet Data Frame (medium dependent) Frame Header Network Header Segment Header Frame Trailer Data Bits 0111111010101100010101101010110001

10. 3) Networking Devices All networks are made up of basic hardware building blocks to interconnect network nodes, such as: • Hubs • Switches • Routers

11. Building a Networking using Hub Hub

12. Building a Networking using Switch Segmentation with Switching Switches

13. Building an Internetworking using Router • An Internetwork is a collection of individual networks, connected by intermediate networking devices, that function as a single large network. • A router is needed to connect individual networks. • Router maintains routing table to keep track of individual networks. Routers

14. Networking Media • Networking media can be defined simply as the means by which signals (data) are sent from one computer to another (either wired or wireless means).

15. Networking Media Physical communications Channels • Twisted Pair • uses copper wire, twisted together in pairs to form a telephone wire. • Maximum segment length of 100 meters • Coaxial Cable/Co-ax • uses one or more central wire conductors surrounded by an insulator and encased in metal sheathing.

16. Networking Media • thin coaxial cable is able to transport a signal up to around 185 meters without line loss. • thick coaxial cable is able to carry signals over long distances: up to 500 meters without line loss • Fiber-optic Cable • A physical communications channel that uses light and glass fibers. • It is light-weight and tolerates data rates on the order of 100Mbps up to 60km.

17. Networking Media Wireless Channels Wireless channels transmit data through air or space • Radio Waves • RF frequency ranges from roughly 30 kilohertz to 1 gigahertz • A radio wave is an electromagnetic wave propagated by an antenna. • All FM radio stations transmit in a band of frequencies between 88 megahertz and 108 megahertz. • Microwave • Microwaves frequency ranges between 1 GH(109 Hz) to 1 TH (1012 Hz).

18. Networking Media • They are the principal carriers of television, telephone, and data transmissions between stations on Earth and between the Earth and satellites. • Radar beams are short pulses of microwaves used to locate ships and planes etc. • Infrared • Transmits data and information by means of an infrared light. The signal cannot travel through objects. • commonly used in remote control of TVs, VCRs and CD players

19. Network Topology

20. Introduction to Computer Networks Network Topology • The network topology defines the way in which computers, printers, and other devices are connected. • LAN topologies define the manner in which network devices are organized.

21. Introduction to Computer Networks Bus Topology • Commonly referred to as a linear bus, all the devices on a bus topology are connected by one single cable. • Broadcast shared media. • Suitable for small networks. • Single point of failure.

22. Introduction to Computer Networks Star & Tree Topology • The star topology is the most commonly used architecture in most LANs. • No single point-of-failure • Larger networks use the extended star topology also called tree topology. • When used with network devices, like bridges, switches, and routers, this topology significantly reduces the traffic on the wires by sending packets only to the wires of the destination host.

23. Introduction to Computer Networks Ring Topology • A frame travels around the ring, stopping at each node. If a node wants to transmit data, it adds the data as well as the destination address to the frame. • The frame then continues around the ring until it finds the destination node, which takes the data out of the frame. • The dual ring topology allows data to be sent in both directions.

24. Introduction to Computer Networks Mesh Topology • The mesh topology connects all devices (nodes) to each other for redundancy and fault tolerance. • Chances of connection break downs are very minimal. • It is used in WANs to interconnect LANs and for mission critical networks like those used by banks and financial institutions. • Implementing the mesh topology is expensive and difficult.

25. Network Classification

26. Network Classification • Based on their size, networks can be classified as: • Local Area Network (LAN) • Metropolitan Area Network (MAN) • Wide Area Network (WAN) • Internet

27. Local Area Network (LAN) • A network covering a small geographic area, like a home, office, or building. • LANs are designed to share resources between personal computers. • The resources to be shared can include hardware (e.g., printer, Scanner), software (e.g., an application program) or data.

28. Metropolitan Area Network (MAN) • A network that connects two or more LANs but does not extend beyond the boundaries of the immediate town/city. • In many cities under the streets, Copper and Fiber Optic cables are run. Above ground we find Wireless, Microwave and Lasers. These technologies are typically limited to distances under 100 miles. These limitations define a MAN or Metropolitan Area Network. Examples: • A network of fire stations in a suburban area would be an example • A newspaper/media company employ a MAN. • A chain of community colleges could be linked by a MAN.

29. Wide Area Network (WAN) • A data communications network that covers a relatively broad geographic area (i.e. one city to another and one country to another). • WAN often uses transmission facilities provided by common carriers, such as telephone companies. • Dedicated transoceanic cabling or satellite uplinks may be used.

30. WAN

31. Modern internetwork

32. Modern Internetwork • There are at least three variants of internetwork, depending on who administers and who participates in them: • Intranet • Extranet • VPN

33. What is an Intranet? • Intranet is an internal network used strictly within the confines of a company, university, or organization. • Belongs to an organization, and is designed to be accessible only by the organization's members, employees, or others with authorization. • An intranet's Web site looks and act just like other Web sites, but has a firewall surrounding it to guard against unauthorized users.

34. What is an Extranet? • An “extended intranet”, uses the Internet to link selected resources of a company’s intranet with its customers, suppliers, or other business partners • Extranet transmissions are conducted over the Internet to save money. But it offers no privacy or transmission security. • By creating tunnels of secure data flows using cryptography and authorization algorithms, called VPNs, the security can be improved.

35. Virtual private network (VPN) • Provide secure connectivity between a corporation’s intranets and intranets of its business partners, material suppliers, financial services, and customers. • Tunneling: the process by which VPNs transfer information by encapsulating traffic in IP packets over the Internet

36. Layered System View Intranet Corporate members Extranet Clients, partners, customers Internet Global society: competitors

37. Network security

38. Common Network Attacks Reading contents of messages is called eavesdropping Difficult to detect Sniffing/Snooping - Monitoring the network for sensitive data and passwords

39. Common Network Attacks Modification or creation of messages (by attackers) Easy to detect but difficult to prevent

40. Common Network Attacks Denial-of-service Attack- Lowering or removing quality of service in a network

41. Common Network Attacks Message Replays - Sending a message repeatedly to a receiver

42. Security Methods Firewalls • A firewall is a part of a network that is designed to block unauthorized access while permitting authorized communications. • It is a device or set of devices that is configured to permit or deny network transmissions based upon a set of rules and other criteria. • All messages entering or leaving the intranet pass through the firewall. • Firewalls can’t protect against malicious insiders viruses, and scans for source & destination addresses & port numbers, not details of data

43. Security Methods • Password-based Authentication • Address-based Authentication (network address) • Personal Tokens (hardware & password/ smart cards) • Biometrics(fingerprint, voiceprint, handwriting) • Antivirus software