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 xDSL (Digital Subscriber Line) A technology that provides digital data transmission over unused frequencies on traditional telephone lines For example, ADSL (Asymmetric DSL): DL > UL Speed Downlink 128Kbps - 4Mbps Uplink 64Kbps - 800Kbps Need a DSL modem Splitters are needed to separate the voice and data signal

18. 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

19. Broadband Services Satellite A technology that provide digital data transmission over satellites Speed Downlink 500Kbps - 1Mbps Uplink 50Kbps - 100Kbps Need a satellite dish

20. 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

21. 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

22. 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

23. 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

24. 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

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

26. VPN (Virtual Private Network) A secure tunnel to a private network through a public network Once established, local node appears to be a node in the private network in a secure manner Correction from the book (pg. 11): VPN does not mean using telephone line connection!!!

27. 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

28. 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/

29. Top-level Domains gTLDs (generic TLDs).com,.edu,.net,.org,.gov,.mil.aero,.biz,.coop,.info,.museum,.name,.pro ccTLDs (country code TLDs).au,.ca,.br,.de,.fi,.fr,.jp,.hk,.cn,.tw,.my, ….us

30. Second-level Domains Domains that are directly below a TLD Eg. ucr.edu google.com sony.co.jp Must apply to a registrar for the appropriate TLD

31. Domain Names & Registrars Profitable domain names CreditCards.com - $2.75M Loans.com – $3M Business.com - $7.5M Network Solutions, Inc used to monopolize the name registration Now, ~500 registrars

32. How To Register A Domain Name? Come up a new name 2 name servers’ IP addresses 1 administrative contact 1 technical contact Register the name to an Internet domain registrar Eg. www.netsol.com, www.godaddy.comwww.godaddy.com Used to be done via email or fax, now all web-based!

33. Policies AUP (Acceptable Use Policies) A legal document, written to protect the ISP from unlawful use of its service, and outlines prohibited uses of the service and possible consequences of misuse Privacy Policies A document describes an ISP’s policy for protecting users’ information

34. 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

35. 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

36. 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

37. What is Multimedia? Dr. Jia Uddin, BRAC University

38. 15-38 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

39. 15-39 Types of Networks Local-area network (LAN) A network that connects a relatively small number of machines in a relatively close geographical area

40. 15-40 Types 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

41. 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

42. 15-42 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

43. 15-43 Types of Networks Metropolitan-area network (MAN) The communication infrastructures that have been developed in and around large cities

44. 15-44 So, who owns the Internet? Well, nobody does. No single person or company owns the Internet or even controls it entirely. As a wide-area network, it is made up of many smaller networks. These smaller networks are often owned and managed by a person or organization. The Internet, then, is really defined by how connections can be made between these networks.

45. 15-45 Types of Networks Figure 15.1 Local-area networks connected across a distance to create a wide-area network

46. 15-46 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

47. 15-47 Internet Connections There are various technologies available that you can use to connect a home computer to the Internet A phone modem converts computer data into an analog audio signal for transfer over a telephone line, and then a modem at the destination converts it back again into data A digital subscriber line (DSL) uses regular copper phone lines to transfer digital data to and from the phone company’s central office A cable modem uses the same line that your cable TV signals come in on to transfer the data back and forth

48. 15-48 Internet Connections Broadband A connection in which transfer speeds are faster than 128 bits per second DSL connections and cable modems are broadband connections The speed for downloads (getting data from the Internet to your home computer) may not be the same as uploads (sending data from your home computer to the Internet)

49. 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

50. 15-50 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

51. 15-51 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

52. 15-52 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

53. 15-53 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

54. 15-54 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

55. 15-55 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)

56. 15-56 MIME Types Related to the idea of network protocols and standardization is the concept of a file’s MIME type MIME stands for Multipurpose Internet Mail Extension Based on a document’s MIME type, an application program can decide how to deal with the data it is given

57. 15-57 MIME Types Figure 15.7 Some protocols and the ports they use

58. 15-58 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

59. 15-59 Firewalls Figure 15.8 A firewall protecting a LAN

60. 15-60 Network Addresses Hostname A unique identification that specifies a particular computer on the Internet For example matisse.csc.villanova.edu condor.develocorp.com

61. 15-61 Network Addresses Network software translates a hostname into its corresponding IP address For example 205.39.145.18

62. 15-62 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

63. 15-63 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

64. 15-64 Domain Name System The very last section of the domain is called its top- level domain (TLD) name Figure 15.10 Top-level domains, including some relatively new ones

65. 15-65 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

66. 15-66 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

67. Topology of Network Dr. Jia Uddin, BRAC University

68. 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

69. 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

70. 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

71. Branching Tree Topology

72. 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)

73. 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

74. 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

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

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