Lecture 16: Multi-path TCP"

Transcription

1 Lecture 16: Multi-path TCP" CSE 222A: Computer Communication Networks Alex C. Snoeren Thanks: Costin Raiciu

2 Lecture 16 Overview" TCP review MPTCP Overview 2

3 TCP Connection Setup HTTP server listening on port 80 3

4 TCP Connection Setup SYN DPORT 80 SPORT

5 TCP Connection Setup SYN/ACK DPORT 80 SPORT

6 TCP Connection Setup ACK DPORT 80 SPORT

7 TCP Data Transmission Browser: Send 3KB of data HTTP Server: Read Request 7

8 TCP Data Transmission Data: Browser: Send 3KB of data HTTP Server: Read Request 8

9 TCP Data Transmission Data: Data: Browser: Send 3KB of data HTTP Server: Read Request 9

10 TCP Data Transmission Data: Data: Data: Browser: Send 3KB of data HTTP Server: Read Request 10

11 TCP: Lost Packets Data: Data: Browser: Send 3KB of data HTTP Server: Read Request 11

12 TCP: Reordering Data: Data: Data: Browser: Send 3KB of data HTTP Server: Read Request 12

13 TCP: Sequence #s and ACKs SEQ 2001 Data: SEQ 1001 Data: SEQ 1 Data: Browser: Send 3KB of data HTTP Server: Read Request 13

14 TCP: Sequence #s and ACKs SEQ 2001 Data: SEQ 1001 Data: ACK 1001 Browser: Send 3KB of data HTTP Server: Read Request 14

15 TCP: Sequence #s and ACKs SEQ 2001 Data: ACK 1001 ACK 2001 Browser: Send 3KB of data HTTP Server: Read Request 15

16 TCP: Sequence #s and ACKs ACK 1001 ACK 2001 ACK 3001 Browser: Send 3KB of data HTTP Server: Read Request 16

17 Multipath TCP" MPTCP is a drop in replacement for TCP Works with unmodified applications Over the existing network 17

18 18" Drop-in TCP Replacement" The sender stripes packets across paths user space socket API MPTCP MPTCP The receiver puts the packets in the correct order IP addr addr 1 addr 2 18

19 MPTCP Operation SYN MP_CAPABLE X 19

20 MPTCP Operation SYN/ACK MP_CAPABLE Y 20

21 MPTCP Operation STATE 1 CWND Snd.SEQNO Rcv.SEQNO 21

22 MPTCP Operation STATE 1 CWND Snd.SEQNO Rcv.SEQNO SYN JOIN Y 22

23 MPTCP Operation STATE 1 CWND Snd.SEQNO Rcv.SEQNO SYN/ACK JOIN X 23

24 MPTCP Operation STATE 1 CWND Snd.SEQNO Rcv.SEQNO STATE 2 CWND Snd.SEQNO Rcv.SEQNO 24

25 MPTCP Operation options SEQ 1000 DSEQ DATA STATE 1 CWND Snd.SEQNO Rcv.SEQNO STATE 2 CWND Snd.SEQNO Rcv.SEQNO 25

26 MPTCP Operation options SEQ 1000 DSEQ DATA STATE 1 CWND Snd.SEQNO Rcv.SEQNO STATE 2 CWND Snd.SEQNO Rcv.SEQNO 26

27 MPTCP Operation options SEQ 1000 DSEQ DATA STATE 1 CWND Snd.SEQNO Rcv.SEQNO SEQ 5000 options DSEQ DATA STATE 2 CWND Snd.SEQNO Rcv.SEQNO 27

28 MPTCP Operation options SEQ 1000 DSEQ DATA STATE 1 CWND Snd.SEQNO Rcv.SEQNO SEQ 5000 options DSEQ DATA STATE 2 CWND Snd.SEQNO Rcv.SEQNO 28

29 MPTCP Operation options SEQ 1000 DSEQ DATA STATE 1 CWND Snd.SEQNO Rcv.SEQNO SEQ 5000 options DSEQ DATA STATE 2 CWND Snd.SEQNO Rcv.SEQNO 29

30 MPTCP Operation options SEQ 1000 DSEQ DATA STATE 1 CWND Snd.SEQNO Rcv.SEQNO SEQ 5000 options DSEQ DATA STATE 2 CWND Snd.SEQNO Rcv.SEQNO 30

31 MPTCP Operation ACK 2000 STATE 1 CWND Snd.SEQNO Rcv.SEQNO STATE 2 CWND Snd.SEQNO Rcv.SEQNO 31

32 MPTCP Operation options SEQ 2000 DSEQ DATA STATE 1 CWND Snd.SEQNO Rcv.SEQNO STATE 2 CWND Snd.SEQNO Rcv.SEQNO 32

33 Pool BW to Balance Load" Each path runs its own congestion control, to detect and respond to the congestion it sees. But link the congestion control parameters, so as to move traffic away from the more congested paths. [Kelly & Voice, Key, Massoulie & Towsley] be less aggressive be more aggressive 33

34 Design goal 1: Be fair to regular TCP" A multipath TCP flow with two subflows Regular TCP To be fair, Multipath TCP should take as much capacity as TCP at a bottleneck link, no matter how many paths it is using. 34

35 Design goal 2: MPTCP should use efficient paths" 12Mb/s 12Mb/s 12Mb/s Each flow has a choice of a 1-hop and a 2-hop path. How should split its traffic? 35

36 Design goal 2: MPTCP should use efficient paths" 12Mb/s 8Mb/s 12Mb/s 8Mb/s 12Mb/s 8Mb/s If each flow split its traffic 1:

37 Design goal 2: MPTCP should use efficient paths" 12Mb/s 9Mb/s 12Mb/s 9Mb/s 12Mb/s 9Mb/s If each flow split its traffic 2:

38 Design goal 2: MPTCP should use efficient paths" 12Mb/s 10Mb/s 12Mb/s 10Mb/s 12Mb/s 10Mb/s If each flow split its traffic 4:

39 Design goal 2: MPTCP should use efficient paths" 12Mb/s 12Mb/s 12Mb/s 12Mb/s 12Mb/s 12Mb/s If each flow split its traffic :

40 Design goal 2: MPTCP should use efficient paths" 12Mb/s 12Mb/s 12Mb/s 12Mb/s 12Mb/s 12Mb/s Theoretical solution (Kelly+Voice 2005; Han, Towsley et al. 2006) MPTCP should send all its traffic on its least-congested paths. " Theorem. This will lead to the most efficient allocation possible, given a network topology and a set of available paths. 40

41 Design goal 3: Perform as well as TCP" wifi path: high loss, small RTT 3G path: low loss, high RTT Design Goal 2 says to send all your traffic on the least congested path, in this case 3G. But this has high RTT, hence it will give low throughput. Goal 3a. A Multipath TCP user should get at least as much throughput as a single-path TCP would on the best of the available paths. Goal 3b. A Multipath TCP flow should take no more capacity on any link than a single-path TCP would. 41

42 Design goals" Goal 1. Be fair to TCP at bottleneck links redundant Goal 2. Use efficient paths... Goal 3. as much as we can, while being fair to TCP Goal 4. Adapt quickly when congestion changes Goal 5. Don t oscillate How does MPTCP achieve all this? 42

43 TCP congestion control" Maintain a congestion window w. Increase w for each ACK, by 1/w Decrease w for each drop, by w/2 43

44 MPTCP congestion control" Maintain a congestion window w r, one window for each path, where r R ranges over the set of available paths. Increase w r for each ACK on path r, by Decrease w r for each drop on path r, by w r /2 44

45 MPTCP congestion control" Maintain a congestion window w r, one window for each path, where r R ranges over the set of available paths. Design goal 3: At any potential bottleneck S that path r might be in, look at the best that a single-path TCP could get, and compare to what I m getting. Increase w r for each ACK on path r, by Decrease w r for each drop on path r, by w r /2 45

46 MPTCP congestion control" Maintain a congestion window w r, one window for each path, where r R ranges over the set of available paths. Design goal 2: We want to shift traffic away from congestion. Increase w r for each ACK on path r, by To achieve this, we increase windows in proportion to their size. Decrease w r for each drop on path r, by w r /2 46

47 Discussion" How much of the Internet can be pooled?» What are the implications for network operators? How should we fit multipath congestion control to CompoundTCP or CubicTCP? Is it worth using multipath for small flows? 47

48 For Next Class " Read and review wireless paper posted later today Keep going on projects! Checkpoint 2 only 1 weeks away 48