characterization of tcp flows over large-fat networks
DESCRIPTION
Characterization of TCP flows over Large-Fat Networks. Antony Antony, Johan Blom, Cees de Laat, Jason Lee, Wim Sjouw University of Amsterdam 03/02/2003. SW. SW. PC. PC. OC 12, 622Mbps. OC 48, 2.5Gbps. SURFnet Amsterdam Chicacgo 96msec, 2001 - 2002. R. R. PC. PC. OC 192, 10 Gbps. - PowerPoint PPT PresentationTRANSCRIPT
1PFLDNet 2003
Characterization of TCP flows over Large-Fat Networks
Antony Antony, Johan Blom,
Cees de Laat, Jason Lee, Wim Sjouw
University of Amsterdam
03/02/2003
2PFLDNet 2003
Networks used
PC SW PCSW
OC 48, 2.5Gbps
OC 12, 622Mbps
SURFnet Amsterdam Chicacgo 96msec, 2001 - 2002
PC PCOC 192, 10 Gbps
SURFnet Amsterdam Chicacgo 96msec, iGrid 2002
R R
PC PC2.4 Gbps
DataTag CERN Chicacgo 110 msec, 2002, till now
R RSW SW
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Layer - 2 requirements from 3/4
TCP is bursty due to sliding window protocol and slow start algorithm.
Window = BandWidth * RTT & BW == slow
fast - slowMemory-at-bottleneck = ----------- * slow * RTT fast
WS WSL2
fast->slowL2
slow->fastfast fast
high RTTslow
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Self-clocking of TCPWS WS
L2fast->slow
L2slow->fast
fast fasthigh RTT
20 µsec14 µsec
20 µsec
20 µsec
20 µsec
(20 of 25)
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Forbidden area, solutions for s when f = 1 Gb/s, M = 0.5 MbyteAND NOT USING FLOWCONTROLs
rtt
158 ms = RTT Amsterdam - Vancouver
OC12
OC9
OC6
OC3
OC1
Possible BW due to lack of buffer at the bottleneck
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Characterising a TCP Flow
• Three different phases of TCP– Bandwidth discovery phase– Steady state– Congestion avoidance
• Is it due to Implementations, Protocol or Philosophical ?
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Modifications
• Faster Host/NIC
• Pacing out Packets at device level.
• HSTCP, using Net100 2.1
• Q length on the Interface (Linux Specific)– IFQ manipulation using Net100– Changing TXQ using ifconfig
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TCP performance comparison.Network Single
StreamMulti Stream UDP
Lambda (622M) 80 540 560
Lambda (1.2G) 120 580 800
iGrid2002 120 580 800
Post iGrid2002
(HSTCP)
730 730 900
DataTag (HSTCP) 950 950 950
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Near GigE using vanilla TCP!
• 980Mbps Sunnyvale to Amsterdam (196 msec)Jumbo Frames, no congestion, entire path was OC192
• Throughput drops when there is congestion– With HSTCP (Net100) flow recovers from
congestion events
Sunnyvale – Chicago – Amsterdam – CERN – Amsterdam196 msec Path
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Conclusion
• Throughput of a TCP flow depend on Slow Start Behavior– If you get early congestion, your flow will probably
not recover before you finish
• TCP is not robust.
• Is this an Implementation , Protocol or Philosophical problem ?
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Future Work
• Higher speed single TCP flows in the WAN– Using 10Gig NICs on the end hosts
• Use traces captured from wire to examine behavior of TCP.
• Closer look at TCP behavior over Lambdas vs. routed networks.