ESLEA Closing Conference, Edinburgh, March 2007, R. Hughes-Jones Manchester 1 Protocols Testing of DCCP at the Application Level Richard Hughes-Jones & Stephen Kershaw The University of Manchester then “Talks”

ESLEA Closing Conference, Edinburgh, March 2007, R. Hughes-Jones Manchester 2 DCCP: Datagram Congestion Control Protocol uUnreliable No re-transmissions uHas modular congestion control Can detect congestion and take avoiding action Different algorithms can be selected – ccid TCP-like TCP Friendly Rate Control Others possible uDCCP is like UDP with congestion control uDCCP is like TCP without reliability uApplication uses Multi-media – send new data instead of re-sending useless old data Applications that can choose data encoding & transmission rate VLBI – discussing a special ccid

ESLEA Closing Conference, Edinburgh, March 2007, R. Hughes-Jones Manchester 3 DCCP: The Application View uStephen & Richard with help from Andrea uPorted udpmon to dccpmon Some system calls don’t work getsockopt(*soc, SOL_DCCP, DCCP_SOCKOPT_CHANGE_L, &dccp_features, &len); uHad problems with Fedora Core 6 using kernel rc1 DCCP data packets never reached the receiving TSAP ! Verify with tcpdump Using development “patches” kernel rc5-g73fd2531-dirty udccpmon tests Plateau ~990 Mbit/s wire rate No packet Loss Receive system crashed! uIperf tests 940Mbps, back-to-back uNeed more instrumentation in DCCP Eg a line in /proc/sys/snmp

ESLEA Closing Conference, Edinburgh, March 2007, R. Hughes-Jones Manchester 4 DCCP: “Latest” Kernel uKernel _pktd-plus - ~2 weeks old then udccpmon tests Receive system crashed even faster ! Just 1 or ,000 packet tests uIperf tests OK short runs 940Mbps, back-to-back Hangs, but runs for longer ! uContact with linux-foundation via PFLDnet2007

ESLEA Closing Conference, Edinburgh, March 2007, R. Hughes-Jones Manchester 5 Porting dccpmon to uDCCP #defines not in the userland include files Use own include files uValues have changed since uSome API calls changed as well uStill no SNMP information uProcess cannot be removed – reboot needed udccpmon being tested

ESLEA Closing Conference, Edinburgh, March 2007, R. Hughes-Jones Manchester 6 Iperf with CCID2 uKernel web100_pktd-plus (64 bit) uIntel e Gigabit NIC uBack-2-back uMTU 1500 bytes uConstant throughput of 940 Mbit/s uMoved 788 GBytes u2 Hrs. CRASH FREE uBut had increased kernel parameter min_free_kbytes to in receiving host (default = 5741) uMin_free_kbytes is the amount of memory available for atomic allocations by the network driver at interrupt level. ukswapd daemon swaps kernel data around to keep this amount of free memory available.

ESLEA Closing Conference, Edinburgh, March 2007, R. Hughes-Jones Manchester 7 Iperf with CCID3 uKernel web100_pktd-plus (64 bit) uIntel e Gigabit NIC uBack-2-back uMTU 1500 bytes umin_free_kbytes = in receiving host u300 kbit/s for 40 min ! uThen constant throughput of 940 Mbit/s

ESLEA Closing Conference, Edinburgh, March 2007, R. Hughes-Jones Manchester 8 Variation with min_free_kbytes uKernel web100_pktd-plus (64 bit) umin_free_kbytes = 5471 [default] in receiving host uIperf can run for about 5mins usually crashes in a few sec umin_free_kbytes = in receiving host uIperf can run for about 2 Hrs

ESLEA Closing Conference, Edinburgh, March 2007, R. Hughes-Jones Manchester 9 DCCP: CCID=SafeUDP [2 0 ] uVLBI has a clear requirement to move CBR data UDP seems ideal Other applications NEED this form of delivery RTP / RTSP Lots of streaming applications available now u Discussed at recent meetings EXPReS & EVN-NREN meeting in Zaandan, NL PFLDnet 2007 / IRTF workshop in Marina Del Rey, US uConcern expressed about UDP overloading the Academic Network uInput from Kees Neggers, SURFnet; Glen Turner, AARNET; Aaron Falk, IRTF Chair

ESLEA Closing Conference, Edinburgh, March 2007, R. Hughes-Jones Manchester 10 DCCP: CCID=SafeUDP [2] uPropose a CCID that is “UDP like” but with Network protection uUse the DCCP ACK mechanism to detect congestion Note: detection of congestion alone is not sufficient uEvaluate congestion: Ensure congestion is in the network not the end hosts. Test if the congestion is transient. uInform the application RTP / RTSP of the congestion Use of new return codes to existing API sendto(), recvfrom(), etc u If, after some time interval, the application takes no action drop the input from the application. Use of new return code to indicate this. uWorking with partners with the aim of a draft RFC

ESLEA Closing Conference, Edinburgh, March 2007, R. Hughes-Jones Manchester 11 Any Questions?