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Transport Protocols: Bulk File TransferStanislav Shalunov 〈[email protected]〉
Steven Senger 〈[email protected]〉ESCC/Internet2 Joint Techs Workshop
Salt Lake City, 2005-02-16
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Bulk Transfers
• The killer application for high-performance networks so far
– What else do we need fat pipes for?
• Several flavors:
– straightforward huge file transfer
– interactive high-throughput applications (e.g., ImmSeg)
– instrument data transfer (e.g., e-VLBI)
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Problem Exists Below Application
• Remains unsolved even in its most simple form (file transfer)
– best current practice: open n TCP streams, send data
– typical current practice: n = 1 (FTP, HTTP, SCP, etc.)
• Expected performance (links are not congested): ˜100Mb/s
• Typical performance: less than 3Mb/s (Abilene)
• The wizard gap gets wider
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Top Reasons of Poor Performance (maybe 80%of cases)
• Bad transport protocols (layer 4)
• Ethernet duplex mismatch (layer 2)
• Bad last-hop cables (layer 1)
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Conventional TCP: Bad Transport
• Fundamental problems:
– Unstable for high-speed networks
– Too sensitive to non-congestive packet loss (even after
minor fixes)
– Before a loss happens, buffers need to fill: delay is at least
doubled
• Implementation problems
– Buffers are laughably small:
∗ Normal default buffer sizes: 8kB, 16kB, 32kB, 64kB
∗ Even 64kB over 70ms limits throughput to 7.5Mb/s
– No provisions for automatic buffer increases
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Remedies for TCP’s maladies
(In increasing order of invasiveness.)
• Tuning: buffers, window scaling, timestamps, SACK
• Use multiple streams
• Something else
• Replace the kernel and use a different congestion control
• Replace all routers and kernels
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Internet2 Transport Effort
• A group of congestion control researchers and high-end users
• Started in late October 2004
• Goal: do better than conventional TCP
• Most immediate deliverable: a design space survey
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Transport tool
• High performance
• Completely end-to-end: no router modifications
• Suitable for both bulk file transfer and interactive multimedia
• Portable, easy to install and use (no kernel modifications)
• Advanced congestion control using existing research
• Tolerance for minor non-congestive packet loss
• Security
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Design Space for the Tool
• Current version: transport-design-space-07.pdf
• Available from http://www.internet2.edu/˜shalunov/transport/
• Copies of -06 on the registration desk
• Specify requirements
• Document independent design questions
• Converge on a design
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Design Space Dimensions
• Explicit signaling
• Implicit signaling
• Kernel- vs user-space
• Protocol features
• Window- vs rate-based
• TCP-compatible vs TCP-friendly
• State at sender vs receiver
• Single vs multiple streams
• UI and API
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Current ideas about the design
• TCP-friendly, not TCP-compatible
• Security nonces
• Implicit congestion signaling
• Delay-based, with fallback to loss-based
• User-space tool with UDP
• State at receiver where possible
• API and a file transfer/distribution application
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What’s your take?
• Your feedback counts
• Mailing list: [email protected]
• Weekly teleconferences: Friday, noon ET
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ImmSeg
• Interactive bulk multimedia transfer
• TCP not suitable
– Partially reliable datagrams
– Unreliable datagrams
– Very fast ramp-up
– Performance
• Requirements shaped by applications such as ImmSeg
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S. Senger / Univ. of Wisc. - La Crosse / ESCC/Internet2 Joint Techs Workshop / Salt Lake City Feb. 05
Immersive SegmentationImmersive Segmentation
¥ Segment/Visualize volumetric data sets
¥ Stereoscopic ray-cast image
¥ Haptically-enabled segmentation tools
¥ Continuous control of remote computation
¥ Exploit userÕs expert interpretive knowledge
¥ Discovery-based pedagogy
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S. Senger / Univ. of Wisc. - La Crosse / ESCC/Internet2 Joint Techs Workshop / Salt Lake City Feb. 0514
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S. Senger / Univ. of Wisc. - La Crosse / ESCC/Internet2 Joint Techs Workshop / Salt Lake City Feb. 0515
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S. Senger / Univ. of Wisc. - La Crosse / ESCC/Internet2 Joint Techs Workshop / Salt Lake City Feb. 05
Collaborative EnvironmentCollaborative Environment
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S. Senger / Univ. of Wisc. - La Crosse / ESCC/Internet2 Joint Techs Workshop / Salt Lake City Feb. 05
Modes of OperationModes of Operation
¥ Region growing
Ð Seed action at a point with initial category
Ð Interactive steering during propagation
¥ Neighborhood cluster
Ð Identify voxel categories in local neighborhood
Ð Heuristically determine opaque category
Ð Visual transition between category changes
Ð Fix category choice and move through volume
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S. Senger / Univ. of Wisc. - La Crosse / ESCC/Internet2 Joint Techs Workshop / Salt Lake City Feb. 05
Visualization StreamVisualization Stream
¥ Pixel updates during user action
¥ Varies by mode, up to 30Mb/s per client
¥ Tolerate small loss
¥ Prefer reliable at close of action
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S. Senger / Univ. of Wisc. - La Crosse / ESCC/Internet2 Joint Techs Workshop / Salt Lake City Feb. 05
Haptics StreamHaptics Stream
¥ Reflect changing segmentation on server
¥ Stream random sample of neighborhood
¥ Client retains last 1/2 second of samples
¥ Unreliable - rate dependent on
Ð neighborhood size
Ð desired density
Ð acceptable age of samples
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S. Senger / Univ. of Wisc. - La Crosse / ESCC/Internet2 Joint Techs Workshop / Salt Lake City Feb. 05
Surface DataSurface Data
¥ Interactively mesh segmented structures
¥ Press against and move over structure
¥ Mesh data streamed to auxiliary client
¥ Reliable, ~40Mb/s bursts
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More information
• http://www.internet2.edu/˜shalunov/transport/
• Join the mailing list: [email protected]
• Send comments on the design space survey
Contributors
Lawrence D. Dunn (Cisco), Yunhong Gu (UIC),
Steven Low (Caltech), Injong Rhee (NCSU),
Bartek Wydrowski (Caltech), Lisong Xu (UNL)
Questions?21