CS5229 09/10 Lecture 9: Internet Packet Dynamics
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    CS5229 09/10 Lecture 9: Internet Packet Dynamics CS5229 09/10 Lecture 9: Internet Packet Dynamics Presentation Transcript

    • Vern Paxson’s Paper" “End-to-End" Internet Packet Dynamics”, 1997/99 22 August 2008 NUS CS5229 Semester 1 1 2008/09
    • How often are packets dropped?" How often are packets reordered?" : 22 August 2008 NUS CS5229 Semester 1 2 2008/09
    • Why these questions? 22 August 2008 NUS CS5229 Semester 1 3 2008/09
    • 1. Understand the Internet 22 August 2008 NUS CS5229 Semester 1 4 2008/09
    • “ when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in ” numbers, your knowledge is of a meagre and unsatisfactory kind; - Lord Kelvin 22 August 2008 NUS CS5229 Semester 1 5 2008/09
    • 2. Model the Internet 22 August 2008 NUS CS5229 Semester 1 6 2008/09
    • 3. Enable more accurate evaluation through simulations 22 August 2008 NUS CS5229 Semester 1 7 2008/09
    • 4. Lead to a better application/systems design 22 August 2008 NUS CS5229 Semester 1 8 2008/09
    • How often are packets dropped?" How often are packets reordered?" : 22 August 2008 NUS CS5229 Semester 1 9 2008/09
    • How to answer these questions? 22 August 2008 NUS CS5229 Semester 1 10 2008/09
    • Collect lots of packet traces" Analyze the traces 22 August 2008 NUS CS5229 Semester 1 11 2008/09
    • Trace collection:" large number of flows" a variety of sites" many packets per flow" use TCP 22 August 2008 NUS CS5229 Semester 1 12 2008/09
    • Why TCP:" real-world traffic" will not overload the network 22 August 2008 NUS CS5229 Semester 1 13 2008/09
    • Time between measurement is Poisson distributed." PASTA Theorem: Intuitively, if we make n observations and k observations is in some state S and n-k in other states, then we can assume prob of observing S is approximately k/n. 22 August 2008 NUS CS5229 Semester 1 14 2008/09
    • Two traces:" N1: Dec94 " N2: Nov-Dec95" use tcpdump at sender + receiver" 22 August 2008 NUS CS5229 Semester 1 15 2008/09
    • 100 kB Size of file transfered 22 August 2008 NUS CS5229 Semester 1 16 2008/09
    • 21 Number of sites 22 August 2008 NUS CS5229 Semester 1 17 2008/09
    • 20800 Number of trace pairs 22 August 2008 NUS CS5229 Semester 1 18 2008/09
    • Part 1:" The Unexpected 22 August 2008 NUS CS5229 Semester 1 19 2008/09
    • Packet Reordering 22 August 2008 NUS CS5229 Semester 1 20 2008/09
    • 1 2 5 2 reorderings 3 4 22 August 2008 NUS CS5229 Semester 1 21 2008/09
    • N1 N2 36% 12% Percentage of connections with at least one out-of-order delivery 22 August 2008 NUS CS5229 Semester 1 22 2008/09
    • N1 N2 2% .3% Percentage of data packets out-of-order 22 August 2008 NUS CS5229 Semester 1 23 2008/09
    • N1 N2 .6% .1% Percentage of ACK packets out-of-order 22 August 2008 NUS CS5229 Semester 1 24 2008/09
    • Data packets are usually sent closer together. 22 August 2008 NUS CS5229 Semester 1 25 2008/09
    • From To 15% .2% Percentage of packets out-of-order to and from U of Colorado in N1. 22 August 2008 NUS CS5229 Semester 1 26 2008/09
    • Route fluttering: alternate packets can take different route to dest. 22 August 2008 NUS CS5229 Semester 1 27 2008/09
    • Taken from Paxson’s PhD Thesis: Alternate routes are taken for packets from WUSTL to U Mannheim 22 August 2008 NUS CS5229 Semester 1 28 2008/09
    • Fig 1 from the paper, showing large gap and two slopes. 22 August 2008 NUS CS5229 Semester 1 29 2008/09
    • T1 (new arrival) Ethernet (buffered packets) Fig 1 from the paper, showing large gap and two slopes. 22 August 2008 NUS CS5229 Semester 1 30 2008/09
    • Impact of Packet Reordering 22 August 2008 NUS CS5229 Semester 1 31 2008/09
    • Recap: TCP’s fast retransmit 22 August 2008 NUS CS5229 Semester 1 32 2008/09
    • S = 1000 S = 2000 S = 3000 S = 4000 A = 2000 S = 5000 A = 2000 A = 2000 A = 2000 S = 2000 22 August 2008 NUS CS5229 Semester 1 33 2008/09
    • S = 1000 S = 2000 S = 3000 S = 4000 A = 2000 S = 5000 A = 2000 A = 2000 A = 2000 S = 2000 22 August 2008 NUS CS5229 Semester 1 34 2008/09
    • Nd = 3 is a conservative choice. 22 August 2008 NUS CS5229 Semester 1 35 2008/09
    • What if receiver wait longer before sending dup ack? 22 August 2008 NUS CS5229 Semester 1 36 2008/09
    • S = 2000 W S = 2000 22 August 2008 NUS CS5229 Semester 1 37 2008/09
    • 1 2 5 Delivery Gap: " time between receiving " 3 an out-of-order packet and " the packet sent before it. 4 22 August 2008 NUS CS5229 Semester 1 38 2008/09
    • Taken from Paxson’s PhD Thesis: CDF for delivery gap between reordered packets. 22 August 2008 NUS CS5229 Semester 1 39 2008/09
    • N2 N1 higher BW 22 August 2008 NUS CS5229 Semester 1 40 2008/09
    • N1 N2 20ms 8ms Waiting time with which 70% of " out-of-order delivery would be identified. 22 August 2008 NUS CS5229 Semester 1 41 2008/09
    • Is needless retransmission a problem? 22 August 2008 NUS CS5229 Semester 1 42 2008/09
    • Good S = 2000 S = 2000 22 August 2008 NUS CS5229 Semester 1 43 2008/09
    • Bad S = 2000 S = 2000 22 August 2008 NUS CS5229 Semester 1 44 2008/09
    • N1 N2 22 300 Number of good retransmissions for every bad retransmission. Nd = 3, W = 0 22 August 2008 NUS CS5229 Semester 1 45 2008/09
    • N1 N2 ~ 7 100 Number of good retransmissions for every bad retransmission. Nd = 2, W = 0 22 August 2008 NUS CS5229 Semester 1 46 2008/09
    • N1 N2 15 300 Number of good retransmissions for every bad retransmission. Nd = 2, W = 20ms 22 August 2008 NUS CS5229 Semester 1 47 2008/09
    • Packet Corruption 22 August 2008 NUS CS5229 Semester 1 48 2008/09
    • 1 in 5000 packet is corrupted 22 August 2008 NUS CS5229 Semester 1 49 2008/09
    • 1 in 65536 corrupted packet goes undetected using TCP checksum (assuming each possible checksum is equally likely) 22 August 2008 NUS CS5229 Semester 1 50 2008/09
    • 1 in 300million Internet packet is corrupted " and is undetected. 22 August 2008 NUS CS5229 Semester 1 51 2008/09
    • Part 2:" Bottleneck Bandwidth 22 August 2008 NUS CS5229 Semester 1 52 2008/09
    • Packet Pair 22 August 2008 NUS CS5229 Semester 1 53 2008/09
    • B bps b bytes 22 August 2008 NUS CS5229 Semester 1 54 2008/09
    • Q x B = b Q s 22 August 2008 NUS CS5229 Semester 1 55 2008/09
    • Q s 22 August 2008 NUS CS5229 Semester 1 56 2008/09
    • Q s 22 August 2008 NUS CS5229 Semester 1 57 2008/09
    • Q s 22 August 2008 NUS CS5229 Semester 1 58 2008/09
    • Problems with Packet Pair 22 August 2008 NUS CS5229 Semester 1 59 2008/09
    • 1. Asymmetric Link 22 August 2008 NUS CS5229 Semester 1 60 2008/09
    • 22 August 2008 NUS CS5229 Semester 1 61 2008/09
    • 2. ACK Compression 22 August 2008 NUS CS5229 Semester 1 62 2008/09
    • 22 August 2008 NUS CS5229 Semester 1 63 2008/09
    • 3. Out of order delivery 22 August 2008 NUS CS5229 Semester 1 64 2008/09
    • 22 August 2008 NUS CS5229 Semester 1 65 2008/09
    • 4. Clock resolution 22 August 2008 NUS CS5229 Semester 1 66 2008/09
    • Suppose B = 1000 kBps b = 1 kB Q = ? 22 August 2008 NUS CS5229 Semester 1 67 2008/09
    • 5. Changing bottleneck bandwidth 22 August 2008 NUS CS5229 Semester 1 68 2008/09
    • Fig 2 from the paper, showing changing bandwidth. 22 August 2008 NUS CS5229 Semester 1 69 2008/09
    • Fig 3 from the paper, showing multi-channel links. 22 August 2008 NUS CS5229 Semester 1 70 2008/09
    • 6. Multi-channel Links 22 August 2008 NUS CS5229 Semester 1 71 2008/09
    • Asymmetric links" ACK compression" Out-of-order delivery" Clock resolution" Changes in bottleneck bandwidth" Multi-channel links" 22 August 2008 NUS CS5229 Semester 1 72 2008/09
    • Measure at receiver:" Asymmetric links" ACK compression" Packet bunch:" Out-of-order delivery" Clock resolution" Changes in bottleneck bandwidth" Multi-channel links 22 August 2008 NUS CS5229 Semester 1 73 2008/09
    • 2Q 22 August 2008 NUS CS5229 Semester 1 74 2008/09
    • Collect multiple estimates, take the most freq occurrence (modes) as the bottleneck bandwidth. 22 August 2008 NUS CS5229 Semester 1 75 2008/09
    • 22 August 2008 NUS CS5229 Semester 1 76 2008/09
    • Part 3:" Packet Loss 22 August 2008 NUS CS5229 Semester 1 77 2008/09
    • N1 N2 2.7% 5.2% Percentage of packets that were lost. 22 August 2008 NUS CS5229 Semester 1 78 2008/09
    • N1 N2 50% 50% Percentage of loss free connections 22 August 2008 NUS CS5229 Semester 1 79 2008/09
    • N1 N2 5.7% 9.2% Loss rate on lossy connections 22 August 2008 NUS CS5229 Semester 1 80 2008/09
    • 17% Loss rate on connections from EU to US 22 August 2008 NUS CS5229 Semester 1 81 2008/09
    • Are packet losses independent? 22 August 2008 NUS CS5229 Semester 1 82 2008/09
    • Compute:" Pu = Pr [ p lost ]" Pc = Pr [ p lost | prev pkt lost ] 22 August 2008 NUS CS5229 Semester 1 83 2008/09
    • Pu Pc 2.8% 49% Loss rate for “queued data pkt” on N1 22 August 2008 NUS CS5229 Semester 1 84 2008/09
    • Fig 6 from the paper, showing outage duration. 22 August 2008 NUS CS5229 Semester 1 85 2008/09
    • Are retransmission redundant? 22 August 2008 NUS CS5229 Semester 1 86 2008/09
    • Unavoidable X ACK 22 August 2008 NUS CS5229 Semester 1 87 2008/09
    • Coarse Feedback 22 August 2008 NUS CS5229 Semester 1 88 2008/09
    • Bad RTO 22 August 2008 NUS CS5229 Semester 1 89 2008/09
    • N1 N2 26% 28% Percentage of retransmissions that" are redundant 22 August 2008 NUS CS5229 Semester 1 90 2008/09
    • 4 44 Unavoidable Coarse Feedback Bad RTO 51 Type of redundant retransmission in N1. 22 August 2008 NUS CS5229 Semester 1 91 2008/09
    • Part 4:" Packet Delay 22 August 2008 NUS CS5229 Semester 1 92 2008/09
    • OTT is not well approximated using RTT/2 22 August 2008 NUS CS5229 Semester 1 93 2008/09
    • ACK Compression 22 August 2008 NUS CS5229 Semester 1 94 2008/09
    • (might affect TCP self-clocking) 22 August 2008 NUS CS5229 Semester 1 95 2008/09
    • sent recv 22 August 2008 NUS CS5229 Semester 1 96 2008/09
    • Sending interval Receiving interval 22 August 2008 NUS CS5229 Semester 1 97 2008/09
    • 22 August 2008 NUS CS5229 Semester 1 98 2008/09
    • 22 August 2008 NUS CS5229 Semester 1 99 2008/09
    • Compression event if ξ < .75 22 August 2008 NUS CS5229 Semester 1 100 2008/09
    • N1 N2 50% 60% Percentage of connection that experiences" at least one compression event. 22 August 2008 NUS CS5229 Semester 1 101 2008/09
    • N1 N2 50% 60% Percentage of connection that experiences" at least one compression event. 22 August 2008 NUS CS5229 Semester 1 102 2008/09
    • 2 Average number of events per connection. 22 August 2008 NUS CS5229 Semester 1 103 2008/09
    • Estimating Available Bandwidth 22 August 2008 NUS CS5229 Semester 1 104 2008/09
    • Qb: time to transit the bottleneck" ψi: expected time spent queuing behind predecessor (derived from sending time)" γi: diff between packet OTT and min OTT 22 August 2008 NUS CS5229 Semester 1 105 2008/09
    • time packet i is sent 22 August 2008 NUS CS5229 Semester 1 106 2008/09
    • 22 August 2008 NUS CS5229 Semester 1 107 2008/09
    • β = 1 means all bandwidth is available." β = 0 means none of the bandwidth is available. 22 August 2008 NUS CS5229 Semester 1 108 2008/09
    • Fig 10 from the paper, showing distribution of available bandwidth. 22 August 2008 NUS CS5229 Semester 1 109 2008/09
    • Conclusion 22 August 2008 NUS CS5229 Semester 1 110 2008/09
    • The numbers in the paper are not important. " (the Internet has changed) 22 August 2008 NUS CS5229 Semester 1 111 2008/09
    • Measurement is difficult but useful 22 August 2008 NUS CS5229 Semester 1 112 2008/09
    • Many new techniques needed (e.g to measure bottleneck bandwidth) 22 August 2008 NUS CS5229 Semester 1 113 2008/09
    • We can improve current design (e.g. TCP if we know more about reordering) 22 August 2008 NUS CS5229 Semester 1 114 2008/09
    • We can identify problem (e.g. packet corruption) 22 August 2008 NUS CS5229 Semester 1 115 2008/09
    • We can better model the behavior (e.g. bursty packet loss) 22 August 2008 NUS CS5229 Semester 1 116 2008/09
    • We can infer much info from just a packet trace (e.g. available bandwidth) 22 August 2008 NUS CS5229 Semester 1 117 2008/09