Protocols Testing of DCCP at the Application Level

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ProtocolsTesting of DCCP at the Application
Level
Richard Hughes-Jones Stephen Kershaw The
University of Manchester www.hep.man.ac.uk/ric
h/ then Talks
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DCCP Datagram Congestion Control Protocol

• Unreliable
• No re-transmissions
• Has modular congestion control
• Can detect congestion and take avoiding action
• Different algorithms can be selected ccid
• TCP-like
• TCP Friendly Rate Control
• Others possible
• DCCP is like UDP with congestion control
• DCCP is like TCP without reliability
• Application 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

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DCCP The Application View

• Stephen Richard with help from Andrea
• Ported udpmon to dccpmon
• Some system calls dont work getsockopt(soc,
  SOL_DCCP, DCCP_SOCKOPT_CHANGE_L, dccp_features,
  len)
• Had problems with Fedora Core 6 using kernel
  2.6.19-rc1
• DCCP data packets never reached the receiving
  TSAP !
• Verify with tcpdump
• Using development patches kernel
  2.6.19-rc5-g73fd2531-dirty
• dccpmon tests
• Plateau 990 Mbit/s wire rate
• No packet Loss
• Receive system crashed!
• Iperf tests
• 940Mbps, back-to-back
• Need more instrumentation in DCCP
• Eg a line in /proc/sys/snmp

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DCCP Latest Kernel

• Kernel 2.6.19_pktd-plus - 2 weeks old then
• dccpmon tests
• Receive system crashed even faster !
• Just 1 or 2 1000,000 packet tests
• Iperf tests
• OK short runs 940Mbps, back-to-back
• Hangs, but runs for longer !

• Contact with linux-foundation via PFLDnet2007

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Porting dccpmon to 2.6.20

• DCCP defines not in the userland include files
• Use own include files
• Values have changed since 2.6.19
• Some API calls changed as well
• Still no SNMP information
• Process cannot be removed reboot needed
• dccpmon being tested

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Iperf with CCID2

• Kernel 2.6.20-web100_pktd-plus (64 bit)
• Intel e1000 1 Gigabit NIC
• Back-2-back
• MTU 1500 bytes
• Constant throughput of 940 Mbit/s
• Moved 788 GBytes
• 2 Hrs. CRASH FREE
• But had increased kernel parameter
  min_free_kbytes to 65535 in receiving host
  (default 5741)
• Min_free_kbytes is the amount of memory
  available for atomic allocations by the network
  driver at interrupt level .
• kswapd daemon swaps kernel data around to keep
  this amount of free memory available.

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Iperf with CCID3

• Kernel 2.6.20-web100_pktd-plus (64 bit)
• Intel e1000 1 Gigabit NIC
• Back-2-back
• MTU 1500 bytes
• min_free_kbytes 65535 inreceiving host
• 300 kbit/s for 40 min !
• Then constant throughput of 940 Mbit/s

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Variation with min_free_kbytes

• Kernel 2.6.20-web100_pktd-plus (64 bit)
• min_free_kbytes 5471 default in receiving
  host
• Iperf can run for about 5mins usually crashes
  in a few sec
• min_free_kbytes 65535 in receiving host
• Iperf can run for about 2 Hrs

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DCCP CCIDSafeUDP 20

• VLBI 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
• Discussed at recent meetings
• EXPReS EVN-NREN meeting in Zaandan, NL
• PFLDnet 2007 / IRTF workshop in Marina Del Rey,
  US
• Concern expressed about UDP overloading the
  Academic Network
• Input from Kees Neggers, SURFnet Glen Turner,
  AARNET Aaron Falk, IRTF Chair

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DCCP CCIDSafeUDP 2

• Propose a CCID that is UDP like but with
  Network protection
• Use the DCCP ACK mechanism to detect congestion
• Note detection of congestion alone is not
  sufficient
• Evaluate congestion
• Ensure congestion is in the network not the end
  hosts.
• Test if the congestion is transient.
• Inform the application RTP / RTSP of the
  congestion
• Use of new return codes to existing API sendto(),
  recvfrom(), etc
• If, after some time interval, the application
  takes no actiondrop the input from the
  application.
• Use of new return code to indicate this.
• Working with partners with the aim of a draft RFC

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• Any Questions?