1. How Fast Is the Internet -- Or – How Long Will It Take To Download That File? John DeDourek July 7-8, 2003

2. Day 1 Schedule How does the Internet work? Introductions Presentation Discussion Tour Network tools

3. Day 2 Schedule How fast is the Internet? Presentation More tools Network measurements

4. Host A Network Medium Host

5. Two Types Of Network Host Point-to-point (full duplex) Host Multiple Access Network

6. Frames Trailer DataHeader Network data is “packaged” in frames (e.g. 1500 bytes for Ethernet)

7. A more complex Ethernet Host Store and Forward Switch Store and Forward Switch

8. Definition Network: an interconnection of hosts such that any host can send a frame “directly” to any other host

9. Limitation For various technical reasons, a network is restricted in various ways Maximum number of hosts Maximum length of “wire” Maximum number of switches (etc.) between two hosts

10. The Internet Idea Interconnect individual networks Any host can send data to any other host, whether on the same network or another network, in the same way

11. Internet HostRouterHost Router Network

12. IP Packet dataheader packet frame packet host net router Etc.

13. Queues Packets or frames in out

14. -> Shared <- Internet HHSHH HH SRRRS

15. UNB ’ s Campus Network Mainly Ethernet at 100 Mbs over copper and 1,000 Mbs (1 Gbs) over fiber Switches (various) and switches combined with routers (Nortel Passport 8600)

16. UNB ’ s External Connections NB/PEI Educational Research Network (other institutions of higher learning in provinces) Alliant (about 45 Mbs over ATM over fiber) CANet4 (about 2.5 Gbs over WDM over fiber)

17. UNB ’ s “ big ” routers For connections to outside networks Juniper M20 routers

18. Tour Steven Birch

19. Tools Linux Command window netstat netstat – i netstat – rn ping traceroute

20. Miscellaneous “ unix ” tools Shell and pipes ( “ | ” ) awk grep head tail grep Etc.

21. So How Fast Is the Internet -- Or – How Long Will It Take To Download That File? Day 2

22. What is the Speed of the Internet? Internet data flows across: Copper wire Fiber Wireless (radio) Physics tells us that these all represent electromagnetic propagation

23. Einstein Says The speed of light, hence the speed of electromagnetic propagation is a constant C = 300 x 10 6 m/s Hence the speed of the Internet is: 300 x 10 6 m/s

24. Well Not Exactly! “ C ” is the speed of propagation in “ free space ” From [Peterson] Copper: 2.3 x 10 8 m/s Fiber: 2.0 x 10 8 m/s Radio: 3.0 x 10 8 m/s “ Speed ” of the Internet is between 2.0 x 10 8 and 3.0 x 10 8 m/s

25. A File to Download 62,728 bytes from Stanford University [pipe]

26. Another File to Download 14,554 bytes from Petosa, Inc., Seattle ??? [accordion]

27. How Long Will It Take To Download? One bit! Distance (driving distance [mapquest]) Stanford: 5288 km Seattle: 5342 km Speed: 2 x 10 8 m/s D / S = 26.4 x 10 -3 s pipe organ D / S = 26.7 x 10 -3 s accordion

28. How Long Will It Take To Download n Bits? Size: 62,728 bytes (pipe organ jpeg) Time for n bits: 62,728 x 8 x 26.4 x 10 -3 13,248 s 3.7 hours! Is this correct?

29. One bit at a time

32. Keeping the Pipe Full

33. Width of a bit Depends on communications technology On 100 Mbps Ethernet: 2.3 m Time to send one bit (length of a bit) 2.3 m / ( 2.3 x 10 8 m/s ) = 1 x 10 -8 s Bits per second 1 bit / (1 x 10 -8 s) = 100 x 10 6 b/s

34. Propagation Delay and Transmission Delay To get all the bits on the wire: Number of bits / Transmission rate = Transmission delay To get the last bit to the other end Distance / speed = Propagation delay 62,728 x 8 / (100 x 10 6 ) + 5,288 x 10 3 / (2.3 x 10 8 ) = 5.0 x 10 -3 + 23 x 10 -3 = 28 x 10 -3 s

35. Error Detection and Packets Data divided into packets; each packet has a header with error detection information,etc. Packet overhead (typical) 1460 bytes of data 66 bytes of header Adds 66 / 1460 = 4.5 % overhead Pipe organ jpeg: 62,728 + 4.5 % x 62,728 = 65,551 bytes

36. Full Mesh Connections My machine has a wire to every other machine on the Internet!!! Consider diameter of conduit to run this many wires into my office!!!

37. Packet Switches Switches ( “ layer 2 ” ) and routers ( “ layer 3 ” ) Store and forward packets

38. Delay Through Store and Forward Networks Delay through each link: Transmission delay + Propagation delay “ Assume ” All links have the same transmission rate All links have the same propagation speed Delay = n x (PackSize / TRate) + TotDist / Speed Number of links = n

39. Calculation “ traceroute ” shows number of routers For pipe organ jpeg: 15 routers No way to know number of switches: Guess: 14 Number of links = 30 Calculation: 30 x (65,551 x 8 / 2.5 Gbs) + 5,288 km / (2 x 10 8 m) = 6.32 x 10 -3 + 26.4 x 10 -3 s = 32.7 x 10 -3 s

40. Sharing Cost and Resources I don ’ t want to pay for the whole Internet myself The others who share the cost “ insist ” on using it to transmit their data too Contention at switches and routers when packets arrive destined for the same outgoing link Queuing delay introduced TotalDelay = TransDelay + PropDelay + QueueDelay Unable to predict queuing delay Pipe organ typical measured RTT (Round TripTime) 90 ms TransDelay = 6.32 ms PropDelay = 26.4 ms

41. Flow Of Data Disk Send Buffers Server Application Receive Buffers Client Application Screen Internet advertised window

42. Flow Control Receive buffer size In operating system Value may be set by application Default determined by operating system Advertised window In every acknowledgement sent from receiver to sender Amount of buffer free BufferSize – AmountStillFull Application may not have read all data yet

43. Effect of Window On Transmission Time Assume “ long path ” i.e. large delay across network (trans + prop + queue) Sender transmits one “ window full ” of packets, then waits Receiver receives a “ window full ” and acknowledges receipt and advertises full window I.e., application is infinitely fast Sender receives acknowledgements and sends another full window of data Effect: one window per round trip time

44. Calculation Typical maximum advertised window (my Windows machine) 8760 bytes Number of “ window fulls ” for pipe organ 62,728 bytes / 8760 bytes = 7 Round trip time is 90 ms Total download time is 7 x 90 = 360 ms Effective transmission time 62,728 bytes / 360 ms = 174 KBs = 1.4 Mbs

45. Congestion and Packet Loss To much contention for a switch or router output port exhausts buffer queue Called congestion Switch or router discards packets TCP attempts to avoid waste involved in transmitting packets which will be discarded Each TCP connection reduces effective transmission rate until no congestion occurs (congestion avoidance) Each connection gets a “ fair share ”

46. TCP Congestion Avoidance Sender maintains a “ congestion ” window Actual window used for transmission is minimum of window advertised by the receiver and the congestion window Congestion window starts at “ one packet ” When an acknowledgement is received, congestion window is increased When a packet is lost (and retransmitted) congestion window is reduced Net transmission rate is WinSize / RTT

47. Pipe Organ

48. Accordion

49. Performance Suggestions All links in a path must be considered Provisioning by your ISP, and their ISPs, etc. are important All system components must be considered Disk, processor, display, etc. The advertised window (under control of the receiver) is important

50. Research Areas Performance of various TCP algorithms under actual Internet conditions Congestion avoidance, selective ack, explicit congestion notification Incorporation of wireless links at the network edge Interaction of TCP traffic with UDP traffic RTP for real time multimedia flow

51. References [Peterson] Peterson, Larry L. and Davie, Bruce S. Computer Networks: A Systems Approach. Morgan Kaufmann, San Francisco, 2000. [pipe] The Organ of Don and Jill Knuth. http://www-cs- faculty.stanford.edu/~knuth/organ/jpeg Accessed, Nov. 22, 2002.http://www-cs- faculty.stanford.edu/~knuth/organ/jpeg [accordion] Petosa Model AM-1100 “ Marocco Jazz ” Accordion. http://www.petosa.com/artistmodels/images/frankmarocco2002 _med.jpg Accessed Nov 22, 2002. http://www.petosa.com/artistmodels/images/frankmarocco2002 _med.jpg [mapquest] Mapquest Driving Directions. http://www.mapquest.com/directions/ Accessed Nov 22, 2002. http://www.mapquest.com/directions/