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Measuring the Congestion Responsiveness of Internet Traffic

Measuring the Congestion Responsiveness of Internet Traffic. Ravi Prasad & Constantine Dovrolis Networking and Telecommunications Group College of Computing Georgia Tech. Outline. Motivation Session arrival models Closed-loop Open-loop Congestion Responsiveness Metric

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Measuring the Congestion Responsiveness of Internet Traffic

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  1. Measuring the Congestion Responsiveness of Internet Traffic Ravi Prasad & Constantine Dovrolis Networking and Telecommunications Group College of Computing Georgia Tech

  2. Outline • Motivation • Session arrival models • Closed-loop • Open-loop • Congestion Responsiveness Metric • Closed-loop Traffic Ratio (CTR) • CTR Measurements • Methodology • Results • Summary

  3. Congestion Responsiveness • Congestion Responsive Traffic: Reduces the offered load in the event of congestion • Conventional wisdom: the Internet traffic is congestion responsive due to TCP • TCP carries more than 90% of Internet traffic • TCP reduces offered load (send window) upon sign of congestion • Negative-feedback loop, stabilizing queuing system • Key modeling unit: persistent flows (they last forever!) • Most Internet flows are non-persistent • Is an aggregate of non-persistent TCP flows congestion responsive?

  4. Receiver Sender Application Response Request Transport Network Flows are generated by users/applications, not by the transport layer! • Examples: user clicks web page, p2p transfers, machine-generated periodic FS synchronization • Session: Set of finite (i.e., non-persistent) flows, generated by single user action • Key issue: session arrival process • Does the session arrival rate reduce during congestion?

  5. Two session arrival models • Closed-loop model • Fixed number of users, each user can generate one session at a time • New session arrival: depends on completion of previous session • E.g., ingress traffic in campus network • Open-loop model • Sessions arrive in network independently of congestion • Theoretically, infinite population of users • E.g., egress traffic at popular Web server 1 2 3 N

  6. Closed-loop model • N users: cycles of transfer and idle periods • S:Average session size • TT : Average transfer duration • TI : Average idle time • Na: Number of active sessions • Congestion responsive • Congestion increases TT : reduces offered load Roffered

  7. Open-loop model • Poisson session arrivals • S:Average session size •  : Session arrival rate • Stable only if  <1 • Congestion unresponsive • Offered load Roffered independent of congestion

  8. Mixed Traffic • Internet traffic: mix of open-loop and closed-loop traffic • Mixed traffic can be characterized by Closed-loop Traffic Ratio (CTR)

  9. Measuring Congestion Responsiveness • Direct congestion responsiveness measurements difficult • Require highly intrusive experiments to cause congestion • Require access at bottleneck link • Alternative: Measure CTR (Closed-loop Traffic Ratio) • Indirect metric for congestion responsiveness • High CTR: more congestion responsive • Low CTR: less congestion responsive

  10. CTR estimation (overview) • Start with packet trace from Internet link • Per-packet: arrival time, src/dst address & ports, size • Focus only on TCP traffic: HTTP and well-known ports • Identify users: • Downloads: user is associated with unique DST address • Uploads: user is associated with unique SRC address • For each user, identify sessions: • Session: one or more connections (“transfers”) associated with same user action • E.g., Web page download: multiple HTTP connections • Classify sessions as open-loop or closed-loop: • Successive sessions from same user: closed-loop • Session from a new user, or session arriving from known user after a long idle period: open-loop

  11. An HTTP 1.1 connection can stay alive across multiple sessions Transfer : Segment of TCP connection that belongs to a single session Intra-transfer packet interarrivals: TCP and network-dependent (short) Inter-transfer packet interarrivals: caused by user actions (long) Classify interarrivals based on Silence Threshold (STH) Intra transfer gap Inter transfer gap From Connections to Transfers 1105126179.423931 163.157.239.61 127.207.1.255 80 2290 1420 T 1380 1105126179.478309 163.157.239.61 127.207.1.255 80 2290 1420 T 1380 1105126179.478438 163.157.239.61 127.207.1.255 80 2290 1420 T 1380 1105126179.478554 163.157.239.61 127.207.1.255 80 2289 1420 T 1380 1105126179.488433 163.157.239.61 127.207.1.255 80 2290 1420 T 1380 1105126179.488666 163.157.239.61 127.207.1.255 80 2289 1420 T 1380 1105126179.488918 163.157.239.61 127.207.1.255 80 2289 1420 T 1380 1105126179.539748 163.157.239.61 127.207.1.255 80 2289 1420 T 1380 1105126179.539870 163.157.239.61 127.207.1.255 80 2290 1420 T 1380 1105126179.539993 163.157.239.61 127.207.1.255 80 2290 1420 T 1380 1105126179.549085 163.157.239.61 127.207.1.255 80 2290 154 T 114 1105126179.549399 163.157.239.61 127.207.1.255 80 2289 1420 T 1380 1105126179.611572 163.157.239.61 127.207.1.255 80 2290 1420 T 1380 1105126179.611702 163.157.239.61 127.207.1.255 80 2289 1420 T 1380 1105126179.612235 163.157.239.61 127.207.1.255 80 2289 1420 T 1380 1105126179.612507 163.157.239.61 127.207.1.255 80 2289 1420 T 1380 1105126179.612752 163.157.239.61 127.207.1.255 80 2290 1420 T 1380 1105126179.613121 163.157.239.61 127.207.1.255 80 2290 1420 T 1380 1105126179.672432 163.157.239.61 127.207.1.255 80 2290 1420 T 1380

  12. Intra transfer gap Inter tranfer gap Silence Threshold (STH) estimation • STH=40sec

  13. <MSI >MSI session 2 session 1 Group transfers from same user in sessions • Intuition: transfers from same session will have short interarrivals (machine-generated) • Minimum Session Interarrival (MSI) threshold • MSI aims to distinguish machine-generated from user-initiated events • MSI = 1-5 seconds 1105126179.423931 163.157.239.61 127.207.1.255 80 2290 1420 T 1380 1105126179.478309 163.157.239.61 127.207.1.255 80 2290 1420 T 1380 1105126179.478438 163.157.239.61 127.207.1.255 80 2290 1420 T 1380 1105126179.478554 163.157.239.61 127.207.1.255 80 2289 1420 T 1380 1105126179.488433 163.157.239.61 127.207.1.255 80 2290 1420 T 1380 1105126179.488666 163.157.239.61 127.207.1.255 80 2289 1420 T 1380 1105126179.488918 163.157.239.61 127.207.1.255 80 2289 1420 T 1380 1105126179.539748 163.157.239.61 127.207.1.255 80 2289 1420 T 1380 1105126179.539870 163.157.239.61 127.207.1.255 80 2290 1420 T 1380 1105126179.539993 163.157.239.61 127.207.1.255 80 2290 1420 T 1380 1105126179.549085 163.157.239.61 127.207.1.255 80 2290 154 T 114 1105126179.549399 163.157.239.61 127.207.1.255 80 2289 1420 T 1380 1105126179.611572 163.157.239.61 127.207.1.255 80 2290 1420 T 1380 1105126179.611702 163.157.239.61 127.207.1.255 80 2289 1420 T 1380 1105126179.612235 163.157.239.61 127.207.1.255 80 2289 1420 T 1380 1105126179.612507 163.157.239.61 127.207.1.255 80 2289 1420 T 1380 1105126179.612752 163.157.239.61 127.207.1.255 80 2290 1420 T 1380 1105126179.613121 163.157.239.61 127.207.1.255 80 2290 1420 T 1380 1105126179.672432 163.157.239.61 127.207.1.255 80 2290 1420 T 1380 Intra transfer gap Inter transfer gap session 3

  14. <MSI >MSI > MTT < MTT Classify sessions as open/closed-loop • First session from a user is always open-loop • Session from a returning user is also open-loop, if it starts • Before last session finish, or • Long time after completion of last session • Long time = MTT: Maximum Think Time 1105126179.423931 163.157.239.61 127.207.1.255 80 2290 1420 T 1380 1105126179.478309 163.157.239.61 127.207.1.255 80 2290 1420 T 1380 1105126179.478438 163.157.239.61 127.207.1.255 80 2290 1420 T 1380 1105126179.478554 163.157.239.61 127.207.1.255 80 2289 1420 T 1380 1105126179.488433 163.157.239.61 127.207.1.255 80 2290 1420 T 1380 1105126179.488666 163.157.239.61 127.207.1.255 80 2289 1420 T 1380 1105126179.488918 163.157.239.61 127.207.1.255 80 2289 1420 T 1380 1105126179.539748 163.157.239.61 127.207.1.255 80 2289 1420 T 1380 1105126179.539870 163.157.239.61 127.207.1.255 80 2290 1420 T 1380 1105126179.539993 163.157.239.61 127.207.1.255 80 2290 1420 T 1380 1105126179.549085 163.157.239.61 127.207.1.255 80 2290 154 T 114 1105126179.549399 163.157.239.61 127.207.1.255 80 2289 1420 T 1380 1105126179.611572 163.157.239.61 127.207.1.255 80 2290 1420 T 1380 1105126179.611702 163.157.239.61 127.207.1.255 80 2289 1420 T 1380 1105126179.612235 163.157.239.61 127.207.1.255 80 2289 1420 T 1380 1105126179.612507 163.157.239.61 127.207.1.255 80 2289 1420 T 1380 1105126179.612752 163.157.239.61 127.207.1.255 80 2290 1420 T 1380 1105126179.613121 163.157.239.61 127.207.1.255 80 2290 1420 T 1380 1105126179.672432 163.157.239.61 127.207.1.255 80 2290 1420 T 1380 Intra transfer gap Inter transfer gap session 2 Open session 3 Close session 1 Open

  15. Robustness to MSI & MTT thresholds • Examined CTR variation in the following ranges: • Minimum Session Interarrival (MSI): 0.5sec-2sec • Maximum Think Time (MTT) : 5min-25min • CTR variation < 0.1 • Linear regression: • CTR/MSI = 0.0232/sec • CTR/MTT = 0.0020/min • We use: • MSI=1sec. • MTT=15min.

  16. Sample CTR measurements

  17. Summary • TCP or TCP-like protocols are necessary but not sufficient for a congestion responsive aggregate • Show importance of arrival process for non-persistent transfers • Focus on open-loop and closed-loop models • Closed-loop Traffic Ratio (CTR) used to characterize traffic in a given link • Measurements show CTR values of 60-80% for most Internet links we examined • Session level feedback could be making internet traffic congestion responsive

  18. Thank you!

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