Characterizing End-to-End Packet Delay and Loss in the Internet

Transcription

1 Characterizig Ed-to-Ed Packet Delay ad Loss i the Iteret Jea-Chrysostome Bolot Xiyu Sog Preseted by Swaroop Sigh Layout Itroductio Data Collectio Data Aalysis Strategy Aalysis of packet delay Aalysis of packet loss Coclusio 1

2 Itroductio Objective: Uderstad packet delay ad loss behavior i the Iteret. Ed to Ed delay is the sum of delays experieced at each hop o the way to the destiatio. Delay = Fixed Compoet (Trasmissio at ode, Propagatio delay) + Variable Compoet ( processig ad queueig delays at ode) Packet Loss Rate due to buffer overflow at the itermediate odes. Itroductio Queueig Network Model: The queue size distributio of the etire etwork of queue is equal to the product of queue size distributio of idividual queues. Fails i real life etworks whe traffic streams merge ad split, packet losses due to buffer overflow,etc.. 2

3 Data Collectio 1 tom.iria.fr 2 t8-gw.iria.fr 3 sophia-gw.atlatic.fr 4 icm-sophia.icp.et 5 Ithaca.NY.NSS.NSF.NET 6 Itahaca1.NY.NSS.NSF.NET 7 ss-sura-eth.sura.et 8 sura8-umd-c1.sura.et 9 csc2hub-gw.umd.edu 10 avwhub-gw.umd.edu Route betwee INRIA ad the UMD i July 1992 The bottleeck lik with a badwidth of 128kb/s Data Collectio Probe packets - NetDy Sed out UDP packets at regular itervals Upo receipt of a probe packets, the itermediate host immediately echoes the packet to the ext oe Ca specify the umber of packets, the size of packets ad the iterval betwee successive packets Size: 32 bytes; iterval: 8, 20, 50, 100, 200, 500 ms 3

4 Data Collectio Probe packets - NetDy Iclude 6-byte timestamp field ad 1-byte # field Source Itermediate Destiatio Packet # Due to problems of clock, use the same source host as destiatio host, the measure roud-trip delay UMD INRIA Data aalysis strategy s : time of sedig out by source host r : time of receivig by destiatio host rtt = r - s : packet roud trip delay δ: regular iterval of sedig out If packet is lost, r is udefied ad rtt = 0 4

5 Data aalysis strategy δ= 50 ms, loss rate = 9 % Time series plot Time series aalysis Data aalysis strategy Solve problems: Model fittig ad predictio Models: AR (autoregressive), MA (movig average), ARMA (auto regressive ad movig average) Fit for situatios where o backgroud ifo is available BUT, differet i this study Much is kow about the system Use differet aalysis methods ad the available ifo to iterpret the observatios Examie the above time series aalysis models 5

6 Model the fixed compoet of the roud trip delay of the packet Aalysis of packet delay Model the variable compoet of this delay Probe traffic D Waitig FIFO queue µ Iteret traffic rtt = D + w + p / µ µ : service rate (bit/s) k : buffer size p : the legth of the periodic probe stream (bit) w : the waitig time of probe packet Aalysis of packet delay Situatio 1: the Iteret traffic load is light (e.g. Telet) w +1 w rtt +1 rtt Now itroduce a ew aalysis method Phase Plot Aalysis other tha Time plot aalysis Phase plae (x,y) x = rtt, y = rtt +1 6

7 Aalysis of packet delay Situatio 1: the Iteret traffic load is light (e.g. Telet) Phase plot of rtt δ= 50 ms (D, D) D 140 ms Aalysis of packet delay Situatio 2: small δ ad a large workload of the Iteret packet (e.g. FTP packets) As soo as the previous packet has bee processed, the ext oe will begi. Wait for more time of B/ µ tha P rtt +1 = rtt + B/ µ Probe traffic D P +k P +2 P +1 P FIFO µ Large Iteret packet B rtt +2 - rtt +1 = (r +2 - s +2 ) - (r +1 - s +1 ) = (r +2 - r +1 ) - (s +2 - s +1 ) = p / µ - δ 7

8 Aalysis of packet delay Situatio 2: small δ ad a large workload of the Iteret packet (e.g. FTP packets) Should kept rtt +k - rtt +k-1 = = rtt +2 - rtt +1 = p / µ - δ < 0 I phase plae, It is the lie y = x + ( p / µ - δ ) The existece of poits o this lie idicates that probe packets accumulate behid large Iteret packets. Aalysis of packet delay Situatio 2: small δ ad a large workload of the Iteret packet (e.g. FTP packets) Phase plot of rtt δ= 50 ms y = x+ (p/µ -δ) x 0 =48 ms x 0 =δ-p/µ=48ms δ = 50 ms p = 32 bytes fi µ 130 kb/s 128 kb/s Bottleeck badwidth Probe packets accumulate behid large Iteret packets 8

9 Aalysis of packet delay δ- p/µ = 490 ms Oly two poits are allocated o the lie of y = x ms, idicatig that cosecutive probe packets almost ever accumulate behid oe aother. Situatio 3: Large δ= 500 ms (Scatter aroud the diagoal) Phase plot of rtt, Aalysis of packet delay (cotd..) Lidley s Recurrece Equatio: Expresses relatioship betwee the waitig time of two successive customers i a sigle chael queue. w 1 = w + y x if w + y x > + 0 Packet arrival +1 x Packet departure w y -1w +1 Time 9

10 Aalysis of packet delay (cotd..) Model ca be thought of as a slotted-time model i which slot boudaries are defied by probe arrival times. Assume Iteret stream cotributes b bits i time t durig the slot, applyig Lidley s equatio, we obtai wb = ( w + P t ) µ + Aalysis of packet delay (cotd..) Applyig recurrece equatio to w +1 ad wb, we obtai, w+ 1 = w + ( P + b ) / µ δ ad hece b = µ ( w + 1 w + δ ) P 10

11 Aalysis of packet delay (cotd..) 1st peak:w +1 -w =P/µ-δ (packets behid large iteret packet) 2d peak: w +1 = w (egligible queuig delays Aalysis of packet delay (cotd..) Arrival time of Iteret stream: w + 1= w + ( P+ b )/ µ δ Iteret arrival occurs durig slot if w +1 - w > 0 11

12 Aalysis of packet loss ulp (ucoditioal loss probability) ulp = P(rtt =0) clp (coditioal loss probability) clp =P(rtt +1 =0/rtt =0) plg (packet loss gap) plg = 1/(1-clp) Aalysis of packet loss δ(ms) ulp clp plg

13 Q & A 13