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The Network Transport layer and the Application or TCP/IP and VLBI Data

The Network Transport layer and the Application or TCP/IP and VLBI Data. Richard Hughes-Jones & Stephen Kershaw The University of Manchester www.hep.man.ac.uk/~rich/ then “Talks” and look for Haystack. Outline. Throughput Tests on Mark5s TCP Memory-2-memory tests CPU Load tests

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The Network Transport layer and the Application or TCP/IP and VLBI Data

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  1. The Network Transport layer and the ApplicationorTCP/IP and VLBI Data Richard Hughes-Jones & Stephen Kershaw The University of Manchesterwww.hep.man.ac.uk/~rich/ then “Talks” and look for Haystack 5 Annual e-VLBI Workshop, 17-20 September 2006, Haystack Observatory R. Hughes-Jones Manchester

  2. Outline • Throughput Tests on Mark5s • TCP Memory-2-memory tests • CPU Load tests • Data delay on a TCP link – How suitable is TCP? • 4th Year MPhys Project • Stephen Kershaw & James Keenan • The effect of distance • Throughput on the 630Mbit JB-JIVE UKLight Link • TCP Performance 5 Annual e-VLBI Workshop, 17-20 September 2006, Haystack Observatory R. Hughes-Jones Manchester

  3. VLBI Application Protocol • VLBI signal wave front • Want to examine the data wave front 5 Annual e-VLBI Workshop, 17-20 September 2006, Haystack Observatory R. Hughes-Jones Manchester

  4. TCP: Data moving - Filling the Pipe • TCP has to hold a copy of data in flight in case of re-transmission • Optimal (TCP buffer) window size depends on: • Bandwidth end to end, i.e. min(BWlinks) i.e. the bottleneck bandwidth • Round Trip Time (RTT) • The number of bytes in flight to fill the entire path: • Bandwidth*Delay Product BDP = RTT*BW • Can increase bandwidth by orders of magnitude Receiver Sender RTT ACK Segment time on wire = bits in segment/BW Time 5 Annual e-VLBI Workshop, 17-20 September 2006, Haystack Observatory R. Hughes-Jones Manchester

  5. Timestamp3 Timestamp4 Packet loss Timestamp5 Data3 Data4 VLBI Application Protocol • VLBI data is produced at Constant Bit Rate TCP & Network Sender Receiver Timestamp1 Timestamp2 Data1 Data2 • Want to examine how TCP moves Constant Bit Rate Data • tcpdelay a test program: • instrumented TCP program emulates sending CBR Data. • Records relative 1-way delay • Record TCP Stack activity with web100 ●●● Time 5 Annual e-VLBI Workshop, 17-20 September 2006, Haystack Observatory R. Hughes-Jones Manchester

  6. Send time sec 1 sec Message number Check the Message Send Times Manchester 4th Year MPhys Project Stephen Kershaw & James Keenan • 10,000 Messages • Message size: 1448 Bytes • Wait time: 0 • TCP buffer 64k • Route:Man-UKL-JIVE-prod-Man • RTT ~26 ms • Slope 0.44 ms/message • From TCP buffer size & RTT Expect: ~42 messages/RTT~0.6ms/message 5 Annual e-VLBI Workshop, 17-20 September 2006, Haystack Observatory R. Hughes-Jones Manchester

  7. 26 messages About 25 us One rtt Message 76 Send time sec Message 102 100 ms Message number Send Time Detail • TCP Send Buffer limited • After SlowStart theTCP Buffer is full • packets sent out in bursts each RTT • Program blocked on sendto() 5 Annual e-VLBI Workshop, 17-20 September 2006, Haystack Observatory R. Hughes-Jones Manchester

  8. 1 way delay 100 ms 100 ms Message number 1-Way Delay • 10,000 Messages • Message size: 1448 Bytes • Wait time: 0 • TCP buffer 64k • Route:Man-UKL-JIVE-prod-Man • RTT ~26 ms 5 Annual e-VLBI Workshop, 17-20 September 2006, Haystack Observatory R. Hughes-Jones Manchester

  9. = 1 x RTT 26 ms 1 way delay 10 ms = 1.5 x RTT 10 ms ≠ 0.5 x RTT Message number 1-Way Delay Detail • Why not just 1 RTT? • After SlowStart TCP Buffer Full • Messages at front of TCP Send Buffer have to wait for next ACKs burst – 1 RTT later • Messages further back in the TCP Send Buffer wait for 2 RTT 5 Annual e-VLBI Workshop, 17-20 September 2006, Haystack Observatory R. Hughes-Jones Manchester

  10. Problem #1 Packet Loss Is it important ? 5 Annual e-VLBI Workshop, 17-20 September 2006, Haystack Observatory R. Hughes-Jones Manchester

  11. 5 Annual e-VLBI Workshop, 17-20 September 2006, Haystack Observatory R. Hughes-Jones Manchester

  12. 5 Annual e-VLBI Workshop, 17-20 September 2006, Haystack Observatory R. Hughes-Jones Manchester

  13. t Packet loss Is TCP is suitable for use in transferring real-time eVLBI data, on a lossy network? 5 Annual e-VLBI Workshop, 17-20 September 2006, Haystack Observatory R. Hughes-Jones Manchester

  14. Packet loss 5 Annual e-VLBI Workshop, 17-20 September 2006, Haystack Observatory R. Hughes-Jones Manchester

  15. Packet loss 5 Annual e-VLBI Workshop, 17-20 September 2006, Haystack Observatory R. Hughes-Jones Manchester

  16. Problem #1 Packet Loss Is it important ? 5 Annual e-VLBI Workshop, 17-20 September 2006, Haystack Observatory R. Hughes-Jones Manchester

  17. 5 ms 1-Way Delay with packet drop • Route:B2B on LAN gig8-gig1 • Ping 188 μs • 10,000 Messages • Message size: 1448 Bytes • Wait times: 0 μs • Drop 1 in 1000 • Manc-JIVE tests showtimes increasing with a “saw-tooth” around 10 s 1 way delay 10 ms Message number 28 ms 800 us 5 Annual e-VLBI Workshop, 17-20 September 2006, Haystack Observatory R. Hughes-Jones Manchester

  18. Summary & Conclusions • Standard TCP not optimum for high throughput long distance links • Packet loss is a killer for TCP • Check on campus links & equipment, and access links to backbones • Users need to collaborate with the Campus Network Teams • Dante Pert • New stacks are stable and give better response & performance • Still need to set the TCP buffer sizes ! • Check other kernel settings e.g. window-scale maximum • Watch for“TCP Stack implementation Enhancements” • TCP tries to be fair • Large MTU has an advantage • Short distances, small RTT, have an advantage • TCP does not share bandwidth well with other streams • The End Hosts themselves • Plenty of CPU power is required for the TCP/IP stack as well and the application • Packets can be lost in the IP stack due to lack of processing power • Interaction between HW, protocol processing, and disk sub-system complex • Application architecture & implementation are also important • The TCP protocol dynamics strongly influence the behaviour of the Application. • Users arenow able to perform sustained 1 Gbit/s transfers 5 Annual e-VLBI Workshop, 17-20 September 2006, Haystack Observatory R. Hughes-Jones Manchester

  19. More Information Some URLs 1 • UKLight web site: http://www.uklight.ac.uk • MB-NG project web site:http://www.mb-ng.net/ • DataTAG project web site: http://www.datatag.org/ • UDPmon / TCPmon kit + writeup: http://www.hep.man.ac.uk/~rich/net • Motherboard and NIC Tests: http://www.hep.man.ac.uk/~rich/net/nic/GigEth_tests_Boston.ppt& http://datatag.web.cern.ch/datatag/pfldnet2003/ “Performance of 1 and 10 Gigabit Ethernet Cards with Server Quality Motherboards” FGCS Special issue 2004 http:// www.hep.man.ac.uk/~rich/ • TCP tuning information may be found at:http://www.ncne.nlanr.net/documentation/faq/performance.html& http://www.psc.edu/networking/perf_tune.html • TCP stack comparisons:“Evaluation of Advanced TCP Stacks on Fast Long-Distance Production Networks” Journal of Grid Computing 2004 • PFLDnet http://www.ens-lyon.fr/LIP/RESO/pfldnet2005/ • Dante PERT http://www.geant2.net/server/show/nav.00d00h002 5 Annual e-VLBI Workshop, 17-20 September 2006, Haystack Observatory R. Hughes-Jones Manchester

  20. More Information Some URLs 2 • Lectures, tutorials etc. on TCP/IP: • www.nv.cc.va.us/home/joney/tcp_ip.htm • www.cs.pdx.edu/~jrb/tcpip.lectures.html • www.raleigh.ibm.com/cgi-bin/bookmgr/BOOKS/EZ306200/CCONTENTS • www.cisco.com/univercd/cc/td/doc/product/iaabu/centri4/user/scf4ap1.htm • www.cis.ohio-state.edu/htbin/rfc/rfc1180.html • www.jbmelectronics.com/tcp.htm • Encylopaedia • http://www.freesoft.org/CIE/index.htm • TCP/IP Resources • www.private.org.il/tcpip_rl.html • Understanding IP addresses • http://www.3com.com/solutions/en_US/ncs/501302.html • Configuring TCP (RFC 1122) • ftp://nic.merit.edu/internet/documents/rfc/rfc1122.txt • Assigned protocols, ports etc (RFC 1010) • http://www.es.net/pub/rfcs/rfc1010.txt & /etc/protocols 5 Annual e-VLBI Workshop, 17-20 September 2006, Haystack Observatory R. Hughes-Jones Manchester

  21. Any Questions? 5 Annual e-VLBI Workshop, 17-20 September 2006, Haystack Observatory R. Hughes-Jones Manchester

  22. Backup Slides 5 Annual e-VLBI Workshop, 17-20 September 2006, Haystack Observatory R. Hughes-Jones Manchester

  23. Receiver Sender Segment n Sequence 1024 Length 1024 RTT ACK of Segment n Ack 2048 Segment n+1 Sequence 2048 Length 1024 RTT ACK of Segment n +1 Ack 3072 Time TCP – providing reliability • Positive acknowledgement (ACK) of each received segment • Sender keeps record of each segment sent • Sender awaits an ACK – “I am ready to receive byte 2048 and beyond” • Sender starts timer when it sends segment – so can re-transmit • Inefficient – sender has to wait 5 Annual e-VLBI Workshop, 17-20 September 2006, Haystack Observatory R. Hughes-Jones Manchester

  24. Comparison of Send Time & 1-way delay 26 messages Message 102 Message 76 Send time sec 100 ms Message number 5 Annual e-VLBI Workshop, 17-20 September 2006, Haystack Observatory R. Hughes-Jones Manchester

  25. 1 way delay – 10000 packets Packet 1214 1 way delay μs ~ 5.5 x RTT 1575 packets Packet number 5 Annual e-VLBI Workshop, 17-20 September 2006, Haystack Observatory R. Hughes-Jones Manchester

  26. 1-Way Delay 724 byte msg • 10,000 Messages • Message size: 724 Bytes • Wait times: 20, 25, 30, 35, 40, 45 μs • TCP buffer 64k 1 way delay 100 ms Message number 5 Annual e-VLBI Workshop, 17-20 September 2006, Haystack Observatory R. Hughes-Jones Manchester

  27. 1-Way Delay 724 bytes Detail • 10,000 Messages • Message size: 724 Bytes • Wait times: 20, 25, 30, 35, 40, 45 μs • TCP buffer 64k • Regular cycle of ~125 packets 1 way delay 100 ms Packet number 5 Annual e-VLBI Workshop, 17-20 September 2006, Haystack Observatory R. Hughes-Jones Manchester

  28. Sender Receiver Zero stats OK done Send data frames at regular intervals Inter-packet time (Histogram) ●●● ●●● Time to receive Time to send Get remote statistics Send statistics: No. received No. lost + loss pattern No. out-of-order CPU load & no. int 1-way delay Signal end of test OK done Time Number of packets n bytes  time Wait time Throughput Measurements • UDP Throughput • Send a controlled stream of UDP frames spaced at regular intervals 5 Annual e-VLBI Workshop, 17-20 September 2006, Haystack Observatory R. Hughes-Jones Manchester

  29. tcpdump / tcptrace • tcpdump: dump all TCP header information for a specified source/destination • ftp://ftp.ee.lbl.gov/ • tcptrace: format tcpdump output for analysis using xplot • http://www.tcptrace.org/ • NLANR TCP Testrig : Nice wrapper for tcpdump and tcptrace tools • http://www.ncne.nlanr.net/TCP/testrig/ • Sample use: tcpdump -s 100 -w /tmp/tcpdump.out host hostname tcptrace -Sl /tmp/tcpdump.out xplot /tmp/a2b_tsg.xpl 5 Annual e-VLBI Workshop, 17-20 September 2006, Haystack Observatory R. Hughes-Jones Manchester

  30. tcptrace and xplot • X axis is time • Y axis is sequence number • the slope of this curve gives the throughput over time. • xplot tool make it easy to zoom in 5 Annual e-VLBI Workshop, 17-20 September 2006, Haystack Observatory R. Hughes-Jones Manchester

  31. Zoomed In View • Green Line: ACK values received from the receiver • Yellow Line tracks the receive window advertised from the receiver • Green Ticks track the duplicate ACKs received. • Yellow Ticks track the window advertisements that were the same as the last advertisement. • White Arrows represent segments sent. • Red Arrows (R) represent retransmitted segments 5 Annual e-VLBI Workshop, 17-20 September 2006, Haystack Observatory R. Hughes-Jones Manchester

  32. TCP Slow Start 5 Annual e-VLBI Workshop, 17-20 September 2006, Haystack Observatory R. Hughes-Jones Manchester

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