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Day 2 – OSI Model

Day 2 – OSI Model. What’s in the phone network?. Phones Wire Switches If you include wireless phones Cell towers Wireless phones. Wireless Telephone System. Phone connections were physical. Terms. Workstation Your computer Server Computer which answers requests Mainframe

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Day 2 – OSI Model

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  1. Day 2 – OSI Model

  2. What’s in the phone network? • Phones • Wire • Switches • If you include wireless phones • Cell towers • Wireless phones

  3. Wireless Telephone System

  4. Phone connections were physical

  5. Terms • Workstation • Your computer • Server • Computer which answers requests • Mainframe • Big server typically accessed remotely • Hub/Switch/Router/Bridge • Device to connect networks • Wire • Used to connect from one location to another

  6. Computer Networks - makeup • Computers • Servers • Network Interface Cards (NICs) • Hubs/Switches/Access Points • Routers/Hubs • Wire (Cat 5) • Phone networks • Fiber Optics • Wireless transmission • Software

  7. The Big Picture of Networks (continued)

  8. LAN Network

  9. Logical Connection • Unlike Physical connection • No wiring actually changed • No moving parts • Connection only exists in software • Computers create virtual connection • Dismantle connection when users are finished. • Phone network is now all logical • All data connections are logical

  10. Where do web pages come from? • Open Internet Explorer (or Firefox, Safari…) • Type in the address of the web site • E.g http://kahuna.clayton.edu/~enda • Wait a moment • Page appears

  11. How does it work? • Web browser: • Lookup DNS name of server • Connects to IP address of server on port, asks for page • Reads resulting page and decides if more pages are now required • E.g. Images, stylesheets… • Presents the information to you.

  12. How does IE know where cnn.com is? • It doesn’t. • IE asks the operating system to do a “DNS lookup” on the name (e.g. www.cnn.com) • This results in an IP address 64.236.24.28 • Now IE asks the operating system to connect to that machine.

  13. So Windows is the smart one? • Well not exactly… • Windows has no idea where the IP is either, it hands the request to its closest networking device • Router • Access Point • Modem

  14. Long sequence of events • Each network device can change the request to suite itself • Pass the request on to the next device • E.g. • Modem -> modem -> router -> router -> router -> router -> web server • The same happens in reverse.

  15. This is complex… • The smart people at the International Organization for Standardization (ISO) came along to describe what happens • They came up with the ISO model • Which helps a little

  16. ISO model

  17. IP • The OSI model is just that a MODEL • There is no real implementation of OSI • Most people today use IP (Internet Protocol) for all communications • IP is a suite of protocols, many of which you use daily • The most common are TCP, UDP and ICMP

  18. TCP/IP • Only 4 layers • No Session. • Application • Application & Presentation • Transport • Transport • Network • Network • Network Access • Datalink & Physical

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