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The Performance Bottleneck Application, Computer, or Network. Richard Carlson Internet2 Part 3. Outline. Why there is a problem What can be done to find/fix problems Tools you can use Ramblings on what’s next. Active Measurement Tools.

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    1. The Performance BottleneckApplication, Computer, or Network Richard Carlson Internet2 Part 3

    2. Outline • Why there is a problem • What can be done to find/fix problems • Tools you can use • Ramblings on what’s next

    3. Active Measurement Tools • Tools that inject packets into the network to measure some value • Available Bandwidth • Delay/Jitter • Loss • Requires bi-directional traffic or synchronized hosts

    4. Passive Measurement Tools • Tools that monitor existing traffic on the network and extract some information • Bandwidth used • Jitter • Loss rate • May generate some privacy and/or security concerns

    5. Tools, Tools, Tools • Ping • Traceroute • Iperf • Tcpdump • Tcptrace • BWCTL • NDT • OWAMP • AMP • Advisor • Thrulay • Web100 • MonaLisa • pathchar • NPAD • Pathdiag • Surveyor • Ethereal • CoralReef • MRTG • Skitter • Cflowd • Cricket • Net100

    6. Network Diagnostic Tool (NDT) • Measure performance to users desktop • Identify real problems for real users • Network infrastructure is the problem • Host tuning issues are the problem • Make tool simple to use and understand • Make tool useful for users and network administrators

    7. Different Host, same switch port • 10 Mbps NIC • Throughput 6.8/6.7 mbps send/receive • RTT 20 ms • Retransmission/Timeouts 25/3 • 100 Mbps NIC • Throughput 84/86 mbps send/receive • RTT 10 ms • Retransmission/Timeouts 0/0

    8. Web100 Project • Joint PSC/NCAR project funded by NSF • ‘First step’ to gather TCP data • Kernel Instrument Set (KIS) • Developed patches Linux kernel • Geared toward wide area network performance • Future steps will automate tuning to improve application performance

    9. NDT’s Web100 Based Approach • Simple bi-directional test to gather E2E data • Gather multiple data variables (a breadth of measurements) • Compare measured performance to analytical values • Translate network values into plain text messages • Geared toward campus area network

    10. SC’04 Real Life Example • Booth having trouble getting application to run from Amsterdam to Pittsburgh • Tests between remote SGI and local PC showed throughput limited to < 20 Mbps • Assumption is: PC buffers too small • Question: How do we set WinXP send/receive buffer

    11. SC’04 Determine WinXP info

    12. SC’04 Confirm PC settings • DrTCP reported 16 MB buffers, but test program still slow, Q: How to confirm? • Run test to SC NDT server (PC has Fast Ethernet Connection) • Client-to-Server: 90 Mbps • Server-to-Client: 95 Mbps • PC Send/Recv Buffer size: 16 Mbytes (wscale 8) • NDT Send/Recv Buffer Size: 8 Mbytes (wscale 7) • Reported TCP RTT: 46.2 msec • approximately 600 Kbytes of data in TCP buffer • Min buffer size / RTT: 1.3 Gbps

    13. SC’04 Local PC Configured OK • No problem found • Able to run at line rate • Confirmed that PC’s TCP buffers were set correctly

    14. SC’04 Remote SGI • Run test from remote SGI to SC show floor (SGI is Gigabit Ethernet connected). • Client-to-Server: 17 Mbps • Server-to-Client: 16 Mbps • SGI Send/Recv Buffer size: 256 Kbytes (wscale 3) • NDT Send/Recv Buffer Size: 8 Mbytes (wscale 7) • Reported RTT: 106.7 msec • Min Buffer size / RTT: 19 Mbps

    15. SC’04 Remote SGI Results • Needed to download and compile command line client • SGI TCP buffer is too small to fill transatlantic pipe (19 Mbps max) • User reluctant to make changes to SGI network interface from SC show floor • NDT client tool allows application to change buffer (setsockopt() function call)

    16. SC’04 Remote SGI (tuned) • Re-run test from remote SGI to SC show floor. • Client-to-Server: 107 Mbps • Server-to-Client: 109 Mbps • SGI Send/Recv Buffer size: 2 Mbytes (wscale 5) • NDT Send/Recv Buffer Size: 8 Mbytes (wscale 7) • Reported RTT: 104 msec • Min Buffer size / RTT: 153.8 Mbps

    17. SC’04 Debugging Results • Team spent over 1 hour looking at Win XP config, trying to verify Buffer size • Single NDT test verified this in under 30 seconds • 10 minutes to download and install NDT client on SGI • 15 minutes to discuss options and run client test with set buffer option

    18. SC’04 Debugging Results • 8 Minutes to find SGI limits and determine maximum allowable buffer setting (2 MB) • Total time 34 minutes to verify problem was with remote SGIs’ TCP send/receive buffer size • Network path verified but Application still performed poorly until it was also tuned

    19. NDT Benefits • End-user based view of network • Can be used to identify performance bottlenecks (could be host problem) • Provides some ‘hard evidence’ to users and network administrators to reduce finger pointing • Doesn’t rely on historical data

    20. Web Based Performance tool • Operates on Any client with a Java enabled Web browser • What it can do • Positively state if Sender, Receiver, or Network is operating properly • Provide accurate application tuning info • Suggest changes to improve performance

    21. Web base Performance tool • What it can’t do • Tell you where in the network the problem is • Tell you how other servers perform • Tell you how other clients will perform

    22. NDT methodology • Identify specific problem(s) that affect end users • Analyze problem to determine ‘Network Signature’ for this problem • Provide testing tool to automate detection process

    23. Duplex Mismatch Detection • Developing analytical model to describe how network operates (no prior art?) • Expanding model to describe UDP and TCP flows • Test models in LAN, MAN, and WAN environments NIH/NLM grant funding

    24. Test environment NDT Srv NDT Clt 100 Mbps Full Duplex 100 Mbps Mismatch Switch Receiver Source • Receiver is put is various states • Switch = full & Host = full or half • Switch = half & Host = full or half

    25. Ethernet transmission strategy • Half Duplex • Use carrier sense signal to determine if link in use • If not, send frame at head of queue • Else, wait for frame to end and send frame • Use collision detection signal to determine if other station also sends • Full Duplex • Send packet at head of queue • Disable carrier sense • Disable collision detection

    26. Analytical Loss-ModelLoss vs Transmission rate

    27. Analytical Loss-ModelLow speed loss vs send rate

    28. UDP Loss-ModelSender view – normal operation

    29. UDP Loss-ModelSender view – lost data pkts

    30. UDP Loss-ModelSender view – lost acks

    31. TCP Operation on LAN • Observed behavior depends on direction of TCP flow and direction of mismatch • Data and ACK packets delivered • Data packets lost and ACKs delayed • ACKs packets lost and Data delayed • Losing ACKs has bigger effect than losing Data packets • Web100 details are only available when NDT server is source and client is sink

    32. Four Cases of Duplex Setting FD-FD FD-HD HD-FD HD-HD

    33. Duplex MismatchSwitch is Full & Host is Half

    34. Tentative Mismatch Detection • Full to Half mismatch detection • Large percentage of duplicate ACKs • Connection spends majority of the time in CwndLimited state • Asymmetric throughput • opposite direction is less

    35. Duplex MismatchSwitch is Half & Host is Full

    36. Tentative Mismatch Detection • Half to Full mismatch detection • Large number of timeouts causes long idle time (RTO x timeout value) • Connection spends majority of the time in CwndLimited state • Asymmetric throughput • opposite direction is greater

    37. Bottleneck Link Detection • What is the slowest link in the end-2-end path? • Monitors packet arrival times using libpacp routine • Use TCP dynamics to create packet pairs • Quantize results into link type bins (no fractional or bonded links) Cisco URP grant work

    38. Normal congestion detection • Shared network infrastructures will cause periodic congestion episodes • Detect/report when TCP throughput is limited by cross traffic • Detect/report when TCP throughput is limited by own traffic

    39. Faulty Hardware/Link Detection • Detect non-congestive loss due to • Faulty NIC/switch interface • Bad Cat-5 cable • Dirty optical connector • Preliminary works shows that it is possible to distinguish between congestive and non-congestive loss

    40. Full/Half Link Duplex setting • Detect half-duplex link in E2E path • Identify when throughput is limited by half-duplex operations • Preliminary work shows detection possible when link transitions between blocking states

    41. Additional Functions and Features • Provide basic tuning information • Basic Features • Basic configuration file • FIFO scheduling of tests • Simple server discovery protocol • Federation mode support • Command line client support • Created project page

    42. Internet2 piPEs Project • Develop E2E measurement infrastructure capable of finding network problems • Tools include • BWCTL: Bandwidth Control wrapper for NLANR Iperf • OWAMP: One-Way Active Measurement • NDT: Network Diagnostic Tool

    43. BWCTL Design Goals • Bandwidth Control Server • Wrapper for Dast Iperf tool • Performs scheduled tests between 11 peers • Supports on-demand tests between peer nodes

    44. Architecture

    45. Specific difficulties UDP • Iperf doesn’t always send at requested rate • Iperf sender hangs (likely Linux/iperf interaction – could be due to signal handling of the bwctl level) • End of session is difficult to detect, which is problematic for a “scheduled” timeslot • Iperf sometimes takes large amounts of time to finish

    46. Specific difficulties TCP • Large pipe to small pipe • Launch a large window • Test waits until completion • Terminate test to remain within schedule • Þ Sets of incomplete tests to interpret • Full mesh presents difficulties for window size selection (and other path specific characteristics) • bwctl uses the peer to peer server connection to deduce a “reasonable” window • If at all possible path specific parameters need to be dynamically configured

    47. Future Possibilities • Server-less client side for end hosts • Closer integration with test engine (iperf API?) • Better error detection • Better timing control (begin and end of test is currently a problem) • 3-party tests (client not on one of the endpoints) • Open source development

    48. Availability • Beta version currently available Mail lists: • bwctl-users • bwctl-announce

    49. OWAMP Design Goals • One-Way-Active-Measurement-Protocol • Possible due to growing availability of good time sources • Wide deployment of “open” servers would allow measurement of one-way delay to become as commonplace as measurement of RTT using ICMP tools such as ping. • Current Draft: draft-ietf-ippm-owdp-07.txt • Shalunov,Teitelbaum,Karp,Boote,Zekauskas • RFC just released • Sample implementation under development Alpha code currently available