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University of Worcester COMP 1321 Digital Infrastructures Week 9

University of Worcester COMP 1321 Digital Infrastructures Week 9. Computer Networks. Presented by Lee Campbell. Learning. “If you can’t explain it simply, you don’t understand it well enough.” Albert Einstein (1879-1955 ). Lecture Topics. Lecture topics.

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University of Worcester COMP 1321 Digital Infrastructures Week 9

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  1. University of Worcester COMP 1321 Digital Infrastructures Week 9 Computer Networks Presented by Lee Campbell

  2. Learning “If you can’t explain it simply, you don’t understand it well enough.” Albert Einstein (1879-1955)

  3. Lecture Topics

  4. Lecture topics • The wonderful world of computer networking: • An introduction to computer networks. • Establishing connectivity. • Network topology (physical and logical). • Network hardware, network interface cards (NIC), cabling, hubs, switches and routers. • OSI model.

  5. Today’s lecture

  6. An Introduction to Computer Networks

  7. What is a computer network? • Network (n & v) : A chain of interconnected computers, machines or operations. • [The Concise Oxford Dictionary of Current English, 1990, Clarendon Press.]

  8. What is a computer network? • A network provides the transportation mechanism for the exchange of data. • Allows network devices to communicate. • Computer networks were not designed with security in mind. • The network provides an adversary/threat the means to achieve their required objectives. • The end-points, applications and information also need to be secured.

  9. Google Data Centre [http://cdn.slashgear.com/wp-content/uploads/2012/10/google-datacenter-tech-02.jpg] [http://cdn.slashgear.com/wp-content/uploads/2012/10/google-datacenter-tech-02.jpg]

  10. Google Data Centre Google Youtube Data Center clip

  11. The purpose of a computer network? Three main purposes of a computer network.

  12. The purpose of a computer network? • [1] Provide connectivity: • Internal and external (the Internet). • Connecting network devices together. • The Internet of Things (IoT). • Location and mapping. • Requires physical components to provide connectivity. Cables, routers, hubs, repeaters, switches and power.

  13. The purpose of a computer network? • [2] Allows communication: • Send emails, documents, files and information. • Instant messaging, blogs, social media & web sites. • Financial transactions. • Video and audio streaming. • Video and audio conferencing/broadcasting. • Controlling cars and homes?

  14. The purpose of a computer network? • [3] Share resources: • Information (many forms), documents and files. • Banking and financial transactions. • Music, photos and videos. • Databases. • Printers. • Ideas, views and opinions.

  15. Devices on the network • Network nodes, end-points, devices and computes: • Traditional network devices: • Terminal, mainframe, server, workstation, PC and printer. • Mobile Devices: • Notebook/laptop, smartphone, mobile phone, desktop Phone, PDA, watch and tablet. • Internet of Things (IoT): • Freeze, cooker, heating, coffee machine, alarm system, home automation (lights, video and music). • Others.

  16. The Internet – UK submarine cable map (2014) [https://gigaom.com/wp-content/uploads/sites/1/2014/01/cable-map-uk.jpg?w=708&quality=80&strip=all]]

  17. The Internet - submarine cable map [http://static.independent.co.uk/s3fs-public/thumbnails/image/2014/03/11/13/submarine-cable-map-2014-x.jpg]

  18. Submarine fibre cable [http://incept.co/img/37EQHAIMED.jpg]

  19. Establishing Connectivity

  20. Comparison of the OSI and TCP/IP models • OSI Model • TCP/IP Model • 7 • Application • 4 • Application • Presentation • 6 • 5 • Session • Transport • 4 • 3 • Transport • 3 • Network • 2 • Internet • Data Link • 2 • Network Access • 1 • 1 • Physical

  21. Transmission Control Protocol- SYN, SYN-ACK and ACK • Open Connection • Close Connection • TCB : Transmission Control Block. • Endpoint IP and PORT values, status of the connection and buffers. [http://www.tcpipguide.com/free/t_TCPConnectionEstablishmentProcessTheThreeWayHandsh-3.htm]

  22. TCP packet (Transport layer) [http://courses.oreillyschool.com/sysadmin5/images/TCP-Header.png]

  23. UDP packet (Transport layer) [http://microchip.wdfiles.com/local--files/tcpip:tcp-vs-udp/TCP_UDP_headers.JPG]

  24. IP packet (Network layer) [http://courses.oreillyschool.com/sysadmin5/images/IP-Header.png]

  25. TCP/IP Packet

  26. The major TCP flags • URG (1 bit) : Indicates that the Urgent pointer field is significant • ACK (1 bit) : Indicates that the Acknowledgment field is significant. All packets after the initial SYN packet sent by the client should have this flag set. • PSH (1 bit): Push function. Asks to push the buffered data to the receiving application. • RST (1 bit): Reset the connection. • SYN (1 bit): Synchronize sequence numbers. Only the first packet sent from each end should have this flag set. Some other flags and fields change meaning based on this flag, and some are only valid for when it is set, and others when it is clear. • FIN (1 bit): No more data from sender.

  27. Ethernet Frame - 802.3 (Data-link layer) [http://core0.staticworld.net/images/idge/imported/article/nww/2008/05/01fig95-100279181-orig.jpg]

  28. Naming and Addressing (1) • All networks need a naming system. • Names and numbers. • No duplicates. • LAN : Internal naming system (DNS, IP, Device Name). • WAN : DNS, IPand Device Name. • “Address” normally numerical. • “Name” normally letters. [Courtesy of R.Henson]

  29. Naming and Addressing (2) • Fulfil the required purpose: • Unique network identity for each device. • Provides destination for data to be sent to. • Provides source location for data sent. [Courtesy of R.Henson]

  30. Media Access Control (MAC) – Data-Link layer Naming • From first IEEE (802) spec…. • use “hardware” (MAC) address of device • Data sent as “frames” • transfer very fast… • Typical MAC address: • xx.xx.xx.xx.xx.xx (where x= a hexadecimal number) [Courtesy of R.Henson]

  31. IP – Network Layer Naming • Originates from TCP/IP naming system: • typical IPv4 name: • x.x.x.x • where x = a number, 0 to 255 decimal. • now IPv6 • IPv4 running out of unique numbers! [Courtesy of R.Henson]

  32. Name Resolution • DNS (Domain Name Service/System): • Domain name to IP. • IP to domain name. • NetBIOS names • Resolve NetBIOS name to IP address. • WINS names (Windows Internet Name Service) • Resolve WINS name to IP address. • ARP protocol • Resolves IP address to MAC address. • Reverse ARP (vice versa). [Courtesy of R.Henson]

  33. Network Practical • Please do not capture packets from the University network – only use the captured files provided in Blackboard. • Please do not compromise University policy in regard to network usage and access. • Wireshark is an open source tool. Please use for the intended purpose.

  34. HTTP Wireshark capture

  35. Network Topology

  36. Network topology • We need a way of describing the physical and logical nature of networks…. • Topology (n) : The way in which constituent parts are interrelated or arranged. Topologies can be either physical or logical in nature. Physical topologies describe how the physical cables run, and how these cables connect to the network devices. Logical topologies describe the movement of data within the physical topology.

  37. Five primary topologies • Bus topology • Logical or physical. • Star topology • Physical only. • Ring topology • Logical or physical.

  38. Five primary topologies • Mesh topology (partial and fully connected) • Logical or physical. • Hybrid • Physical.

  39. Bus topology (1)

  40. Star topology (2)

  41. Ring topology (3)

  42. Mesh topology (4.1)

  43. Fully connected mesh topology (4.2)

  44. Hybrid topology (5)

  45. LAN, MAN and WAN • Local Area Network (LAN): • Interconnecting network devices in a limited area, a building or buildings. • Metropolitan Area Network (MAN): • A network that interconnects users in a geographical area or region such as a town or city. A MAN is smaller than a WAN but bigger than a LAN. • Wide Area Network (WAN): • A WAN spans a larger geographical area. Most WANs are constructed from several LANs connected together.

  46. LAN, MAN and WAN [http://www.gta.ufrj.br/ensino/eel879/trabalhos_vf_2008_2/igorcamp/LAN_MAN_WAN.JPG]

  47. Advantages and disadvantages of topologies

  48. LAN and WAN topologies • Local Area Networks (LANs) usually use a Star topology. • Wide Area Networks (WANs) usually use a Mesh topology. • Why? [Courtesy of R.Henson]

  49. Network Hardware

  50. Physical components of a network (1) Firewalls Switches Routers [Images cursory of Cisco.]

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