1 / 58

Networking

Networking. Introduction. Networking - Introduction. Computers are lucky… …but this is not trivial!. Networking - Introduction. RAM. CPU. Easy…. Networking - Introduction. My smartphone in Denmark. www.surf.au in Australia. Hard…. Networking - Introduction.

dolan
Download Presentation

Networking

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Networking Introduction

  2. Networking - Introduction • Computers are lucky… • …but this is not trivial!

  3. Networking - Introduction RAM CPU Easy….

  4. Networking - Introduction My smartphone in Denmark www.surf.au in Australia Hard….

  5. Networking - Introduction • Networking – transmitting data between physically separated computers • No networking – no Internet • The Internet is ”just another computer network” • We will discuss networking within the context of the Internet

  6. Networking - Introduction • What does the Internet look like…? ? My device

  7. Networking - Introduction • What does the Internet look like…? ? My device A Computer

  8. Networking - Introduction • What does the Internet look like…? ? Client Server

  9. Networking - Introduction • Through the Internet, my device (the client) can exchange data with a remote computer (the server) • How is the the client ”connected” to the server?

  10. Networking - Introduction • What does the Internet look like…? C S Client Server Routers

  11. Networking - Introduction • Client is connected to a router C • Server is connected to a router S • Client sends data to C • C sends data to another router, who in turn sends data to another router, etc. • At some point, data reaches the router S • The server gets the data from S • How hard can it be…?

  12. Networking - Introduction • Questions… • How do C and S get to know each other? • How does data find its way from C to S? • What format should data have? • How fast will the data get there? • Can we be sure that the data will reach S? • Can we be sure that the data is not altered? • …?

  13. Networking - Introduction • Communication requires a protocol • This is true for both humans and computers! Hi Hi Do you have the time? Yes, it is 4.30pm Okay, thank you You’re welcome

  14. Networking - Introduction • What can go wrong…? Hi … Я не говорю по английски Oh, I guess he doesn’t speak English…

  15. Networking - Introduction • What can go wrong…? Hi Hmmm, maybe he didn’t hear me… I’ll try again in a minute…

  16. Networking - Introduction • What can go wrong…? Hi I’m busy! I’ll try again in a minute…

  17. Networking - Introduction • What can go wrong…? Hi Hi Do you have the time? Yes, it is &.3¤p? Hmmm, I’ll have to ask him again…

  18. Networking - Introduction • A protocol is about agreement • When has a connection been established • What is the proper format of the transmitted data • What to do when data has been sent • What to do when data has been received • What is the proper order of data • When can data be considered lost • When can a connection be considered broken

  19. Networking - Introduction • What is a connection really…? • Logical aspect • Connection-oriented service • Connectionless service • Physical aspect • Circuit switching • Packet switching

  20. Networking - Introduction • Connection-oriented service • A (logical) way of communication, with certain properties • All data will be delivered • All data will be delivered in the correct order • Nobody ”floods” the counterpart with data • No part of the connection becomes congested

  21. Networking - Introduction • Connection-oriented service Are you ready to receive data? Sure, go ahead OK, here is part 1 of data OK, I got part 1 OK, here is part 2 of data OK, I got part 2 …and so on (handshaking)

  22. Networking - Introduction • Connection-oriented service Here is part n of data Hmmm, I have to send part n again… Here is part n of data OK, I got part n

  23. Networking - Introduction • Connection-oriented service Here is part n of data OK, I got part n Here is part n+1 of data Whoa, slow down a bit! OK, I will send data more slowly

  24. Networking - Introduction • Connection-oriented service • Many good properties, BUT… • More control data is sent • Cannot ”skip” data • Speed of transmission is uncertain

  25. Networking - Introduction • Connectionless service • A (logical) way of communication, with certain properties • No guarantee on delivery • No handshaking • No flow or congestion control • BUT, can potentially deliver data faster

  26. Networking - Introduction • Connectionless service Are you ready to receive data? Sure, go ahead OK, bla bla bla bla bla bla…

  27. Networking - Introduction • Why would we ever use a connectionless service? • Where could it be appropriate? • Sending E-mail? • File transmission • Viewing a web page • Streaming audio • Streaming video

  28. Networking - Introduction • Why would we ever use a connectionless service? • Where could it be appropriate? • Sending E-mail? • File transmission • Viewing a web page • Streaming audio • Streaming video

  29. Networking - Introduction • On the Internet…

  30. Networking - Introduction • Circuit switching • Like in the old days…

  31. Networking - Introduction • Using circuit switching, a dedicated end-to-end circiut is set up C S Client Server

  32. Networking - Introduction • Using circuit switching, a dedicated end-to-end circiut is set up C S Client Server

  33. Networking - Introduction • Properties of circuit switching • Guaranteed transmission rate • Wasteful in idle periods • Best for transmissions with low transmission rate variation (phonecall?) • Very wasteful for ”burst” transmissions

  34. Networking - Introduction • Packet switching • The postal approach…

  35. Networking - Introduction • In packet switching, we no longer use dedicated connnections • A recipient of data has an address • Data is divided into packets, which are ”stamped” with the destination address • The magic lies in the router…

  36. Networking - Introduction • Delivering a letter… Sender Postbox Letterbox Sender Local post office Local post office Regional post office Regional post office National post center National post center

  37. Networking - Introduction Router must choose a destination router… 1 R 2 68.122.87.224 (DATA) 3

  38. Networking - Introduction • Router maintains a routing table of appropriate desitination routers for a given destination adress (or interval of addresses) • How is the routing table created…? • MAGIC…for now 

  39. Networking - Introduction • On the Internet, the IP (Internet Protocol) uses packet switching • Formally, the IP implements a datagram network – a specific variant of packet switching

  40. Networking - Introduction • Circuit Switching vs. Packet Switching • I have a 100 megabit/second (mbps) connection available (bandwidth guaranteed) • I want to give all my users a 10 mbps connection • How many users can share the connection?

  41. Networking - Introduction • Circuit Switching guarantees the bandwidth at all times! • Everybody must be guaranteed a 10 mbit connection… • …so the answer must be 100/10 = 10 users

  42. Networking - Introduction • In packet switching, packets are sent • With full transmission rate • Intermixed with packets from other users • No guaranteed bandwidth • We have to know about the expected use of bandwidth per user

  43. Networking - Introduction • Theoretical use per day, given a 10 mbps connection: • 10 mbps ≈ 1 megabyte/sec • 1 megabyte/sec ≈ 4 gigabyte/hour • 4 gigabyte/hour ≈ 100 gigabyte/day • In practice, probably much less!

  44. Networking - Introduction • Bandwidth usage for a typical (?) private user • 10 gigabyte/month • Peak: 1 gigabyte/day • 00-08: ≈ 10 % • 08-16: ≈ 20 % • 16-24: ≈ 70 %

  45. Networking - Introduction • What is my required ”level of service”? • Specified bandwidth available • 50 % of the time? • 90 % of the time? • 99 % of the time? • 99,99 % of the time?

  46. Networking - Introduction • We wish to cover ”peak usage”, but assume that bandwidth usage during peak time is constant… • Peak usage: 1 gigabyte/day, 70 % between 16-24 • 700 megabyte within 8 hours • 90 megabyte within an hour • 25 kilobytes per second… • about 250 kilobits per second (0,25 mbps)

  47. Networking - Introduction • A 100 mbps connection… • …and a ”peak average” of 0,25 mbps… • …gives about 400 users • Circuit switching: 10 users • Packet switching: 400 users • ..if our assumptions hold up!

  48. Networking - Introduction • Now we know about two protocols • TCP – implements connection-oriented service • IP – implements datagram packet switching • Is that enough to e.g. implement a Web browser…? • Still too low-level, we need a protocol ”on top of” TCP • Enter HTTP

  49. Networking - Introduction • HTTP – HyperText Transfer Protocol • Specifically developed for ”distributed, hypermedia-based information systems” • Developed by Tim Berners-Lee (and team) around 1990 • HTTP + HTML + URL = WWW (almost )

  50. Networking - Introduction • HTTP is essentially just a set of methods that can be executed within a program • First HTTP version – one method! (GET) • Current version has nine methods

More Related