A Quantitative View: Delay, Throughput, Loss

Transcription

1 A Quantitative View: Delay, Throughput, Loss Antonio Carzaniga Faculty of Informatics University of Lugano September 27, 2017

2 Outline Quantitative analysis of data transfer concepts for network applications Propagation delay and transmission rate Multi-hop scenario

3 Quantifying Data Transfer How do we measure the speed and capacity of a network connection?

4 Quantifying Data Transfer How do we measure the speed and capacity of a network connection? Intuition watermovinginapipeline carsmovingalongaroad

5 Quantifying Data Transfer How do we measure the speed and capacity of a network connection? Intuition watermovinginapipeline carsmovingalongaroad Delay or Latency thetimeittakesforonebittogothroughtheconnection(fromoneendtothe other)

6 Quantifying Data Transfer How do we measure the speed and capacity of a network connection? Intuition watermovinginapipeline carsmovingalongaroad Delay or Latency thetimeittakesforonebittogothroughtheconnection(fromoneendtothe other) Transmission rate or Throughput theamountofinformationthatcangetinto(oroutof)theconnectioninatime unit

7 Delay (Latency) and Rate (Throughput) connection

8 Delay (Latency) and Rate (Throughput) message connection

9 Delay (Latency) and Rate (Throughput) connection t 0 first bit enters

10 Delay (Latency) and Rate (Throughput) connection t 0 first bit enters t 1 first bit exists

11 Delay (Latency) and Rate (Throughput) connection t 0 first bit enters t 1 first bit exists t 2 last bit exits

12 Delay (Latency) and Rate (Throughput) connection lbits { }} { t 0 first bit enters t 1 first bit exists t 2 last bit exits

13 Delay (Latency) and Rate (Throughput) connection lbits { }} { t 0 first bit enters t 1 first bit exists t 2 last bit exits PropagationDelay d prop =t 1 t 0 sec

14 Delay (Latency) and Rate (Throughput) connection lbits { }} { t 0 first bit enters t 1 first bit exists t 2 last bit exits PropagationDelay d prop =t 1 t 0 sec Transmission Rate R = l t 2 t 1 bits/sec

15 Delay (Latency) and Rate (Throughput) connection lbits { }} { t 0 first bit enters t 1 first bit exists t 2 last bit exits PropagationDelay d prop =t 1 t 0 sec Transmission Rate R = l t 2 t 1 bits/sec Totaltransfertime d end-end =d+ l R sec

16 Howlongdoesittaketotranferafilebetween,say,LuganoandZürich? Examples

17 Examples Howlongdoesittaketotranferafilebetween,say,LuganoandZürich? Howbigisthisfile?Andhowfastisourconnection?

18 Examples Howlongdoesittaketotranferafilebetween,say,LuganoandZürich? Howbigisthisfile?Andhowfastisourconnection? E.g., a(short) message l = 4Kb d prop = 500ms R = 1Mb/s d end-end =?

19 Examples Howlongdoesittaketotranferafilebetween,say,LuganoandZürich? Howbigisthisfile?Andhowfastisourconnection? E.g., a(short) message l = 4Kb d prop = 500ms R = 1Mb/s d end-end = 500ms+4ms =504ms

20 Howaboutabigfile?(E.g.,amusiccollectionof50songs) Examples

21 Examples Howaboutabigfile?(E.g.,amusiccollectionof50songs) l = 400Mb d prop = 500ms R = 1Mb/s d end-end =?

22 Examples Howaboutabigfile?(E.g.,amusiccollectionof50songs) l = 400Mb d prop = 500ms R = 1Mb/s d end-end = 500ms+400s =400.5s =6 40

23 Examples Howaboutabigfile?(E.g.,amusiccollectionof50songs) l = 400Mb d prop = 500ms R = 1Mb/s d end-end = 500ms+400s =400.5s =6 40 Howaboutabiggerfile?(E.g.,a32GbSSD)

24 Examples Howaboutabigfile?(E.g.,amusiccollectionof50songs) l = 400Mb d prop = 500ms R = 1Mb/s d end-end = 500ms+400s =400.5s =6 40 Howaboutabiggerfile?(E.g.,a32GbSSD) l = 32Gb d prop = 500ms R = 1Mb/s d end-end =?

25 Examples Howaboutabigfile?(E.g.,amusiccollectionof50songs) l = 400Mb d prop = 500ms R = 1Mb/s d end-end = 500ms+400s =400.5s =6 40 Howaboutabiggerfile?(E.g.,a32GbSSD) l = 32Gb d prop = 500ms R = 1Mb/s d end-end = ǫ s =8h53 20

26 HowaboutgoingtoZürichonaVespa? Examples

27 Examples HowaboutgoingtoZürichonaVespa? youcarry500,32-gbmemorycardsinyourbackpack foursecondstotakethecardsoutofyourbackpack

28 Examples HowaboutgoingtoZürichonaVespa? youcarry500,32-gbmemorycardsinyourbackpack foursecondstotakethecardsoutofyourbackpack l = 32Gb d prop =? R = d end-end =

29 Examples HowaboutgoingtoZürichonaVespa? youcarry500,32-gbmemorycardsinyourbackpack foursecondstotakethecardsoutofyourbackpack l = 32Gb d prop = 6h R =? d end-end =

30 Examples HowaboutgoingtoZürichonaVespa? youcarry500,32-gbmemorycardsinyourbackpack foursecondstotakethecardsoutofyourbackpack l = 32Gb d prop = 6h R = 4Tb/s d end-end =?

31 Examples HowaboutgoingtoZürichonaVespa? youcarry500,32-gbmemorycardsinyourbackpack foursecondstotakethecardsoutofyourbackpack l = 32Gb d prop = 6h R = 4Tb/s d end-end = 6h

32 Examples HowaboutgoingtoZürichonaVespa? youcarry500,32-gbmemorycardsinyourbackpack foursecondstotakethecardsoutofyourbackpack l = 32Gb d prop = 6h R = 4Tb/s d end-end = 6h IfyouneedtotransferacoupleofSSDcardsfromLuganotoZürich,andtimeis crucial...thenyoumightbebetteroffridingyourvespatozürichratherthan using the Internet. Formorethan5cards,youmightalsopreferthePostoffice!

33 Two Hops, Stream

34 H 1 X H 2 Two Hops, Stream

35 d 1,R 1 d 2,R 2 H 1 X H 2 Two Hops, Stream

36 d x d 1,R 1 d 2,R 2 H 1 X H 2 Two Hops, Stream

37 Two Hops, Stream d x d 1,R 1 d 2,R 2 H 1 X H 2 (R 1 <R 2 ) d end-end =d 1 + l R 1

38 Two Hops, Stream d x d 1,R 1 d 2,R 2 H 1 X H 2 (R 1 <R 2 ) d end-end =d 1 + l R 1 +d x

39 Two Hops, Stream d x d 1,R 1 d 2,R 2 H 1 X H 2 (R 1 <R 2 ) d end-end =d 1 + l R 1 +d x +d 2 sec

40 Two Hops, Stream d x d 1,R 1 d 2,R 2 H 1 X H 2 (R 1 <R 2 ) d end-end =d 1 + l R 1 +d x +d 2 sec (R 1 R 2 )

41 Two Hops, Stream d x d 1,R 1 d 2,R 2 H 1 X H 2 (R 1 <R 2 ) d end-end =d 1 + l R 1 +d x +d 2 sec (R 1 R 2 ) d end-end =d 1 +d x +d 2 + l R 2 sec d end-end =d 1 +d x +d 2 + l min{r 1,R 2 } sec

42 Two Hops, Store-And-Forward

43 H 1 X H 2 Two Hops, Store-And-Forward

44 d 1,R 1 d 2,R 2 H 1 X H 2 Two Hops, Store-And-Forward

45 d x d 1,R 1 d 2,R 2 H 1 X H 2 Two Hops, Store-And-Forward

46 Two Hops, Store-And-Forward d x d 1,R 1 d 2,R 2 H 1 X H 2 d end-end =d 1 + l R 1

47 Two Hops, Store-And-Forward d x d 1,R 1 d 2,R 2 H 1 X H 2 d end-end =d 1 + l R 1 +d x

48 Two Hops, Store-And-Forward d x d 1,R 1 d 2,R 2 H 1 X H 2 d end-end =d 1 + l R 1 +d x + l R 2

49 Two Hops, Store-And-Forward d x d 1,R 1 d 2,R 2 H 1 X H 2 d end-end =d 1 + l R 1 +d x + l R 2 +d 2

50 Two Hops, Store-And-Forward d x d 1,R 1 d 2,R 2 H 1 X H 2 d end-end =d 1 + l R 1 +d x + l R 2 +d 2 d d p,r x d d p,r x d d p,r x d x H 1 X 1 X 2 X 3 X N

51 Two Hops, Store-And-Forward d x d 1,R 1 d 2,R 2 H 1 X H 2 d end-end =d 1 + l R 1 +d x + l R 2 +d 2 d d p,r x d d p,r x d d p,r x d x H 1 X 1 X 2 X 3 X N ( d end-end =N d p + l ) R +d x

52 Queuing Delay ConsiderarouterwithprocessingrateR x andtotaldelayd x Whathappenswithanarrivalrateλ in >R x?

53 Queuing Delay ConsiderarouterwithprocessingrateR x andtotaldelayd x Whathappenswithanarrivalrateλ in >R x? Theroutercannotprocesspacketsfastenough,sotherouterputspacketsina queue: where d x =d cpu +d queue d queue = q /R x

54 Queuing Delay ConsiderarouterwithprocessingrateR x andtotaldelayd x Whathappenswithanarrivalrateλ in >R x? Theroutercannotprocesspacketsfastenough,sotherouterputspacketsina queue: where d x =d cpu +d queue d queue = q /R x queue length output rate

55 Queuing Delay ConsiderarouterwithprocessingrateR x andtotaldelayd x Whathappenswithanarrivalrateλ in >R x? Theroutercannotprocesspacketsfastenough,sotherouterputspacketsina queue: where d x =d cpu +d queue d queue = q /R x queue length output rate...r x isalsotherateatwhichpacketsgetoutofthequeue

56 Queuing Delay

57 Queuing Delay Ideal case: constant input data rate λ in <R x Inthiscasethed queue =0,because q =0

58 Queuing Delay Ideal case: constant input data rate λ in <R x Inthiscasethed queue =0,because q =0 Extreme case: constant input data rate λ in >R x Inthiscase q = (λ in R x )tandtherefore d queue = λ in R x R x t

59 Queuing Delay

60 Queuing Delay Steady-state queuing delay d queue = 0 λ in <R x λ in R x R x t λ in >R x

61 Queuing Delay Steady-state queuing delay d queue = 0 λ in <R x λ in R x R x t λ in >R x d queue λ in R x ideal input flow λ in constant

62 Queuing Delay Steady-state queuing delay d queue = 0 λ in <R x λ in R x R x t λ in >R x d queue d queue λ in R x ideal input flow λ in constant λ in R x realistic input flow λ in variable

63 Queuing Delay

64 Queuing Delay Conclusion:astheinputrateλ in approachesthemaximumthroughputr x, packets will experience very long delays

65 Queuing Delay Conclusion:astheinputrateλ in approachesthemaximumthroughputr x, packets will experience very long delays More realistic assumptions and models finite queue length(buffers) in routers packets are dropped

66 Queuing Delay Conclusion:astheinputrateλ in approachesthemaximumthroughputr x, packets will experience very long delays More realistic assumptions and models finite queue length(buffers) in routers packets are dropped R x λ out λ in

67 Queuing Delay Conclusion:astheinputrateλ in approachesthemaximumthroughputr x, packets will experience very long delays More realistic assumptions and models finite queue length(buffers) in routers packets are dropped λ out R x congestion λ in