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An Analysis of AIMD Algorithm with Decreasing Increases

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End-to-end approach. Rate based control. The sending rate is tuned per ... Satisfies max-min fairness if all the flows have the same end-to-end link capacity ... – PowerPoint PPT presentation

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Title: An Analysis of AIMD Algorithm with Decreasing Increases


1
An Analysis of AIMD Algorithm with Decreasing
Increases
  • Yunhong Gu, Xinwei Hong, and Robert L. Grossman

National Center for Data Mining
2
Outline
  • TCPs inefficiency in grid applications
  • Improvements on AIMD
  • AIMD with decreasing increases (DAIMD)
  • The UDT algorithm
  • Experimental result
  • Conclusion and future work

3
TCP and AIMD
  • AIMD (Additive Increase Multiplicative Decrease)
  • Fair max-min fairness
  • Stable globally asynchronously stable
  • But, inefficient and not scalable
  • In grid networks (with high bandwidth-delay
    product)

4
Efficiency of TCP
1 Gb/s link, 200ms RTT, between Tokyo and Chicago
28 minutes
On 10 Gb/s link, 200ms RTT, it will take 4 hours
43 minutes to recover from a single loss.
TCPs throughput model It needs extremely low
loss rate on high bandwidth-delay product
networks.
5
Improvements of TCP
  • Fixed parameter (e.g., 1 segment per RTT) is not
    scalable and hence inefficient
  • 32 segments per RTT works fine for 1 Gb/s link,
    but how about its performance on 40Gb/s link or
    1.5Mb/s link?
  • Increasing the increase parameter as the
    congestion window increases
  • E.g., Scalable TCP and HighSpeed TCP
  • Cause fairness and convergence problem

6
AIMD with Decreasing Increases
  • To reach high efficiency, the increase parameter
    of an AIMD-based algorithm should be correlated
    to the link capacity and the available bandwidth.
  • XCP uses available bandwidth and number of
    concurrent flows to calculate next increase
    parameter
  • The increase parameter should be large at the
    beginning and decreases as the sending rate
    increases.

7
AIMD with Decreasing Increases
8
UDT - UDP based Transport Protocol
  • Application level built above UDP
  • End-to-end approach
  • Rate based control
  • The sending rate is tuned per constant interval
    (SYN).

9
UDT Algorithm
  • UDT considers end-to-end link capacity L
  • It is hard to estimate the number of concurrent
    flows and real-time available bandwidth
  • UDT tunes the increase parameter according to
    L-C, where C is the current sending rate.

10
UDT Algorithm
(1) (2) (3) (4) (5)
11
UDT Algorithm
L 10 Gbps, S 1500 bytes
C (Mbps) L - C (Mbps) Increment (pkts/SYN)
0, 9000) (1000, 10000 10
9000, 9900) (100, 1000 1
9900, 9990) (10, 100 0.1
9990, 9999) (1, 10 0.01
9999, 9999.9) (0.1, 1 0.001
9999.9 lt0.1 0.00067
12
UDT Algorithm
13
UDT Efficiency and Fairness Characteristics
  • Takes 7.5 seconds to reach 90 of the link
    capacity, independent of BDP
  • Satisfies max-min fairness if all the flows have
    the same end-to-end link capacity
  • Otherwise, any flow will obtain at least half of
    its fair share
  • Does not take more bandwidth than concurrent TCP
    flow as long as

14
Experiment - Setup
15
Experiment - Results
16
Conclusion
  • Standard TCP is inefficient for grid applications
    in high bandwidth-delay product networks.
  • We argued that the increase parameter should be
    correlated to such information as link capacity
    and available bandwidth.
  • We analyzed a class of AIMD based control
    algorithm whose increase parameter is decreasing
    as the sending rate increases and proved that it
    is fair and stable.
  • According to this analysis we designed a new
    control algorithm that uses estimated link
    capacity and the current sending rate as the
    hints to update increase parameter.
  • This algorithm has been implemented in our UDT
    protocol and the experiments have demonstrated
    very good performance.

17
Future Work
  • Bandwidth Estimation
  • Currently UDT uses packet pairs to estimate link
    capacity
  • We will consider more methods to deal with cross
    traffic and NIC interrupt coalescence

18
Thank you!
  • Questions and comments are welcome!
  • For more information, please visit
  • http//www.ncdm.uic.edu
  • http//udt.sf.net
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