TCP and WANs

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C O M P U T A T I O
N A L R E S E A R
C H D I V I S I O N
TCP and WANs Jason R. Lee 10.3.03
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Overview

• TCP 101
• Experiments
• Alternatives
• Conclusion

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TCP 101

• TCP (Transmission Control Protocol)
• Greedy try to obtain the best utilization
• Fair Allow everyone to get their fair share of
  the network
• Two important states slow-start,
  congestion-control
• Slow Start
• For every good ACK (pkt that got through) add one
  more pkt to the congestion window

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TCP 101

• Congestion Control
• if congestion cwd cwd x 0.5
• otherwise cwd cwd 1 (MTU)
• TCP is AIMD
• AI 1
• MD 0.5

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TCP 101
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TCP Problems
1500 Byte MTU (pkt), 200 ms RTT
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Other TCP

• Virtual Jumbo Fames (large AI)
• Grid DT
• HSTCP (Floyd) (Table based)
• Scalable TCP (Kelly) (cwnd 1.05)

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IFQ Problem

• IFQ Interface Queue
• Default is 100 pkts!
• Too small for WAN

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IFQ, AIMD, HSTCP
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Experiments

• 1 MSS/RTT response function is too slow
• HSTCP is better for Gbps, RTT 100 msc
• Questions
• Is it possible to do better?
• Is it fair to other streams?

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Setup over SURFnet Lambda
Host A
6509
Host B
RTT 200msec
GigE
ONS1545 Amsterdam
ONS1545 Chicago
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HSTCP AI 32 MSS (1Gbps)
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HSTCP AI 256 MSS (1Gbps)
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HSTCP AI 32 MSS(622Mbps)
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HSTCP AI 256MSS(622mbps)
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Big Burst
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Scalable TCP
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Scalable
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LBL -gt ORNL
TCP, HSTCP, Scalable
Done by Tom Dunigan
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LBNL gt ORNL
by Tom Dunigan ORNL
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Faster
10 Gigabits
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TCP Single Stream 5.22 Gbps, 32 MByte Socket
Itanium UvA
RTT 17 msec
Itanium CERN
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UDPish

• UDP Data Transfer UDT
• part of SABUL and Dataspace
• Stream Control Transmission Protocol (SCTP)
• In linux now!!
• Datagram Congestion Control Protocol (DCCP)
• Performance Transparency Protocol (PTP)

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UDT

• Using UDP Datagrams and TCP for retransmission
• Memory to Memory, also support transfer of
  files(not tested)
• http//sourceforge.net/projects/dataspace/
• Authors claim both intra-protocol fairness (it
  uses AIMD-like congestion control mechanism), as
  well as inter-protocol fairness
• FC Bandwidth ( RTT 0.01 ) / MTU

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UDT Multi-stream
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References

• RFC 793
• RFC 1122
• RFC 2001
• http//www-lce.eng.cam.ac.uk/ctk21/scalable/
• http//www.ietf.org/internet-drafts/draft-ietf-tsv
  wg-highspeed-01.txt