1. Computer Communications and Networks CSE- 705 Dr. Jia Uddin Assistant Professor, CSE, BRAC University Dr. Jia Uddin, BRAC University

2. Syllabus Dr. Jia Uddin, BRAC University CSE705: Computer Communications and Networks Queuing models for circuit switching packet switching and protocols, Digital switching, Traffic analysis, Network synchronization, control and management, Fiber optics, Networks, Gigabit networks, Metropolitan and Wide area networking, Network security; Real-time protocols, Network agents, recent advances in internet protocols. Asynchronous transfer mode (ATM) protocols and service categories, Quality of services, ATM traffic management call admission control, Congestion control, Video steams on ATM, ATM switch architecture and their performances. Spread spectrum techniques, Mobile communications: CDMA, GSM, CDPD; Wireless LAN, Wireless ATM, Wireless personal communications. (3 credits)

3. Text Books Dr. Jia Uddin, BRAC University 1.Recommended Text Books: Data & Computer Communications -- William Stallings 2.Data Communications and Networks -- Forouzan

4. What is Computer Network? Dr. Jia Uddin, BRAC University Computer network A collection of computing devices that are connected in various ways in order to communicate and share resources Usually, the connections between computers in a network are made using physical wires or cables However, some connections are wireless, using radio waves or infrared signals

5. Home Network (single machine) USB/Ethernet Cable DSL/Cable Modem Wall Jack

6. Home Network (multiple machines) USB/Ethernet Cable DSL/Cable Modem Wall Jack Hub/Switch/Router

7. Home Network (multiple machines) Ethernet Cable DSL/Cable Modem Wall Jack Hub/Switch/Router

8. Home Wireless Network Ethernet Cable DSL/Cable Modem Wall Jack Hub/Switch/Router

9. Connection Types Computer networks can be classified according to their size: –Personal area network (PAN) –Local area network (LAN) –Metropolitan area network (MAN) –Wide area network (WAN)

10. Personal Area Network A PAN is a network that is used for communicating among computers and computer devices (including telephones) in close proximity of around a few meters within a room It can be used for communicating between the devices themselves, or for connecting to a larger network such as the internet PAN’s can be wired or wireless PAN’s can be wired with a computer bus such as a universal serial bus: USB (a serial bus standard for connecting devices to a computer-many devices can be connected concurrently) PAN’s can also be wireless through the use of bluetooth (a radio standard designed for low power consumption for interconnecting computers and devices such as telephones, printers or keyboards to the computer) or IrDA (infrared data association) technologies

11. LAN (Local Area Network) A network of computers that are in the same physical location, such as home or building Usually connected using Ethernet A standard on how computers communicate over a shared media (cable) http://en.wikipedia.org/wiki/Image:Ethernet_RJ45_connector_p1160054.jpghttp://en.wikipedia.org/wiki/Image:BNC_connector.jpg Old: BNC connector for coaxial cable New: RJ45 for twisted pair cable

12. LAN (Local Area Network) Ethernet Standard 10BaseT(Twisted Pair Ethernet) 10Mbps (Mega bits per second) 100BaseT(Fast Ethernet ) 100Mbps 1000BaseT(Gigabit Ethernet over copper wiring) 1000Mbps or 1Gbps

13. WLAN (Wireless LAN) Wi-Fi (Wireless Fidelity) A wireless technology that connects computers without cables Access Point (AP) A device (base station) that connects wireless devices together Usually connected to a wired-network ESSID (Extended Service Set ID) A “name” for the AP, e.g. mobile net Hotspot The area covered by wireless access points

14. WLAN (Wireless LAN) Standard 802.11b - 11Mbps 802.11g - 54Mbps 802.11a - 54Mbps Security WEP (Wired Equivalen Privacy) WPA (Wi-Fi Protected Access) To prevent wardriving 2.4G 5G

15. Dial-up Services Modem Modulator/demodulator A device that converts analog signal to digital (modulation) and vice versa (demodulation) Speed 1200/2400/9600 bps 14.4/28.8/33.6 Kbps 56 Kbps

16. Dial-up Services ISDN Integrated Services Digital Network 2 data channel (56K each) 1 voice channel

17. Broadband Services Cable A technology that provides digital data transmission over cable TV infrastructure Speed Downlink 128Kbps - 3~5Mbps Uplink 64Kbps - 128Kbps~1Mbps Need a cable modem

18. WAN (Wide Area Network) A LAN spans a large geographic area, such as connections between cities Usually connected using leased line T1 (1.5Mbps) T3 (45Mbps) OC3 (155Mbps) OC12 (622Mbps) OC48 (2.4Gbps) Fiber optic lines Telecommunication lines

19. Hub/Switch/Router To connect multiple segments of networks into a larger one Hub A multiport repeater to enhance signal within the same LAN Switch Like hub but with intelligent Better performance Router Forward packets from one LAN to another

20. Intranet vs. Internet Intranet A private network that is contained within an enterprise Could be LANs and WANs Internet A public network of networks Both are using TCP/IP

21. TCP/IP A family of protocols that makes the Internet works The Robustness Principle “Be liberal in what you accept, and conservative in what you send” - Jon Postel

22. TCP/IP (cont) Application Layer Eg. WWW, FTP, IRC, Email, telnet, … Transport Layer Eg. TCP, UDP Network Layer Eg. IP Link Layer Eg. Ethernet, WiFi Physical Layer Eg. Ethernet Cable, fiber-optics Segments Packets Frames Bits Data

23. Packets A small chunk of data transmitted over the Internet Alice The Internet Bob

24. Host & IP Address Correction from the book: “A host is a computer connected directly to the Internet” “You home computer is not a host” Each host needs an IP address IP address A 32-bit number, arranged in 4 numbers seperated by “.” Eg. 74.125.19.147

25. DNS (Domain Name System) Domain name to IP address conversion Eg. www.google.com → ??.???.??.??www.google.com Domain name or IP address lookup http://cqcounter.com/whois/

26. Networking Dr. Jia Uddin, BRAC University The generic term node or host refers to any device on a network Data transfer rate The speed with which data is moved from one place on a network to another Data transfer rate is a key issue in computer networks

27. Bandwidth Data rate measured in bits (not bytes) per seconds Kbps (Kilobits per seconds) 125 chars/sec Mbps (Megabits per seconds) 1,250 chars/sec Gbps (Gigabits per seconds) 12,500 chars/sec

28. Networking Dr. Jia Uddin, BRAC University Computer networks have opened up an entire frontier in the world of computing called the client/server model Figure 15.1 Client/Server interaction

29. 15-29 Networking File server A computer that stores and manages files for multiple users on a network Web server A computer dedicated to responding to requests (from the browser client) for web pages

30. 15-30 Topology of Networks Various configurations, called topologies, have been used to administer LANs Ring topology A configuration that connects all nodes in a closed loop on which messages travel in one direction Star topology A configuration that centers around one node to which all others are connected and through which all messages are sent Bus topology All nodes are connected to a single communication line that carries messages in both directions

31. Types of Networks A bus technology called Ethernet has become the industry standard for local-area networks Figure 15.2 Various network topologies 15-10

32. 15-32 Types of Networks Wide-area network (WAN) A network that connects two or more local-area networks over a potentially large geographic distance Often one particular node on a LAN is set up to serve as a gateway to handle all communication going between that LAN and other networks Communication between networks is called internetworking The Internet, as we know it today, is essentially the ultimate wide-area network, spanning the entire globe

33. 15-33 Types of Networks Figure 15.1 Local-area networks connected across a distance to create a wide-area network

34. 15-34 Internet Connections Internet backbone A set of high-speed networks that carry Internet traffic These networks are provided by companies such as AT&T, GTE, and IBM Internet service provider (ISP) A company that provides other companies or individuals with access to the Internet

35. Packet Switching To improve the efficiency of transferring information over a shared communication line, messages are divided into fixed- sized, numbered packets Network devices called routers are used to direct packets between networks Figure 15.4 Messages sent by packet switching 15-18

36. 15-36 Open Systems Proprietary system A system that uses technologies kept private by a particular commercial vendor One system couldn’t communicate with another, leading to the need for Interoperability The ability of software and hardware on multiple machines and from multiple commercial vendors to communicate Leading to Open systems Systems based on a common model of network architecture and a suite of protocols used in its implementation

37. 15-37 Open Systems The International Organization for Standardization (ISO) established the Open Systems Interconnection (OSI) Reference Model Each layer deals with a particular aspect of network communication Figure 15.5 The layers of the OSI Reference Model

38. 15-38 Network Protocols Network protocols are layered such that each one relies on the protocols that underlie it Sometimes referred to as a protocol stack Figure 15.6 Layering of key network protocols

39. 15-39 TCP/IP TCP stands for Transmission Control Protocol TCP software breaks messages into packets, hands them off to the IP software for delivery, and then orders and reassembles the packets at their destination IP stands for Internet Protocol IP software deals with the routing of packets through the maze of interconnected networks to their final destination

40. 15-40 TCP/IP (cont.) UDP stands for User Datagram Protocol It is an alternative to TCP The main difference is that TCP is highly reliable, at the cost of decreased performance, while UDP is less reliable, but generally faster

41. 15-41 High-Level Protocols Other protocols build on the foundation established by the TCP/IP protocol suite Simple Mail Transfer Protocol (SMTP) File Transfer Protocol (FTP) Telnet Hyper Text Transfer Protocol (http)

42. 15-42 Firewalls Firewall A machine and its software that serve as a special gateway to a network, protecting it from inappropriate access Filters the network traffic that comes in, checking the validity of the messages as much as possible and perhaps denying some messages altogether Enforces an organization’s access control policy

43. 15-43 Firewalls Figure 15.8 A firewall protecting a LAN

44. 15-44 Network Addresses Hostname A unique identification that specifies a particular computer on the Internet For example matisse.csc.villanova.edu condor.develocorp.com

45. 15-45 Network Addresses Network software translates a hostname into its corresponding IP address For example 205.39.145.18

46. 15-46 Network Addresses An IP address can be split into network address, which specifies a specific network host number, which specifies a particular machine in that network Figure 15.9 An IP address is stored in four bytes

47. 15-47 Domain Name System A hostname consists of the computer name followed by the domain name csc.villanova.edu is the domain name A domain name is separated into two or more sections that specify the organization, and possibly a subset of an organization, of which the computer is a part Two organizations can have a computer named the same thing because the domain name makes it clear which one is being referred to

48. 15-48 Domain Name System Organizations based in countries other than the United States use a top-level domain that corresponds to their two-letter country codes Figure 15.11 Some of the top-level domain names based on country codes

49. 15-49 Domain Name System The domain name system (DNS) is chiefly used to translate hostnames into numeric IP addresses DNS is an example of a distributed database If that server can resolve the hostname, it does so If not, that server asks another domain name server

50. Network Topologies Bus Topology Each node is connected one after the other (like christmas lights) Nodes communicate with each other along the same path called the backbone

51. Ring Topology The ring network is like a bus network, but the “end” of the network is connected to the first node Nodes in the network use tokens to communicate with each other Backbone

52. Star Topology Each node is connected to a device in the center of the network called a hub The hub simply passes the signal arriving from any node to the other nodes in the network The hub does not route the data Hub

53. Branching Tree Topology

54. Access Control Methods Two primary access control methods exist for computers to communicate with each other over the network Token based access Carrier Sense Multiple Access with Collision Detection (CSMA/CD)

55. Token based access Used in bus and ring network topologies (token ring) Each computer in the network can only send its data if it has the token. This prevents collisions that occur when data is sent at the same time over the network The token is a special pattern of bits/bit in a frame that is directly detectible by each node in the network A computer may only transmit information if it is in possession of the token The message is sent to all other computers in the network

56. Operation of token ring As an example, suppose node # 1 wants to send information to node # 4 over the network Initially, an empty frame circulates in the network 1 2 3 4 5 6

57. Routing and Routing Protocols Dr. Jia Uddin, BRAC University

58. Q&A Dr. Jia Uddin, BRAC University