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TCP performance. John Hicks TransPAC HPCC Engineer Indiana University. APAN 19 Meeting – Bangkok, Thailand 27-January-2005. 700. Throughput Mbps. Reno. RTT ms. RTT (~70ms). 0. 1200 s. Standard TCP. Low performance on fast long distance paths

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tcp performance
TCP performance

John Hicks

TransPAC HPCC Engineer

Indiana University

APAN 19 Meeting – Bangkok, Thailand 27-January-2005

standard tcp


Throughput Mbps


RTT ms

RTT (~70ms)


1200 s

Standard TCP
  • Low performance on fast long distance paths
    • AIMD (add a=1 pkt to cwnd / RTT, decrease cwnd by factor b=0.5 in congestion)

Information courtesy of Les Cottrell from the SLAC group at Stanford

standard tcp problems
Standard TCP problems
  • It has long been recognized that TCP does not provide good performance for applications on networks with a high bandwidth delay product.
  • Some things that contribute to this include:
    • Slow linear increase by one packet per RTT.
    • Too drastic multiplicative decrease.
    • Packet level oscillation due to packet loss.
standard tcp improvements
Standard TCP improvements
  • One approach to improving TCP performance is to adjust the TCP window size to be the bandwidth delay product of the network.
    • This approach usually requires a network expert.
    • Hard to achieve in practice.
  • Another approach is to stripe TCP over several standard TCP network connections.
    • This is approach plateaus as the number of sockets increase.
improving data rates
Improving data rates
  • There are basically three categories of projects to improve data transfer rates:
    • Rate limited
      • Examples include: (Robert Grossman) SABUL, RBUDP, and (Steve Wallace) Tsunami.
    • Congestion window limited
      • Examples include: (Steven Low ) FAST, (Tom Kelly) Scalable, (Sally Floyd) Highspeed, and (Injong Rhee) BicTCP.
    • Hardware changes
      • Examples include: XCP

One proving ground for these activities is the Bandwidth Challenge at the Supercomputing Conference

one of the sc04 bwc winners
One of the SC04 BWC winners
  • All Roads Lead Through Chicago to Pittsburgh Performance Award: High Speed TeraByte Transfers for Physics California Institute of Technology, Stanford Linear Accelerator Lab and Fermi National Lab. Over 100 Gb/s per second aggregate memory to memory bandwidth utilizing the greatest number of networks
  • “Caltech, SLAC, Fermilab, CERN, Florida and Partners in the UK, Brazil and Korea Set 101 Gigabit Per Second Mark During the SuperComputing 2004 Bandwidth Challenge”
  • This group used FAST TCP as a transfer mechanism.
fast tcp
  • Based on TCP Vegas
  • Uses both queuing delay and packet losses as congestion measures
  • Developed at Caltech by Steven Low and collaborators
  • Code available at: http://

Information courtesy of Les Cottrell from the SLAC group at Stanford

scalable tcp
Scalable TCP
  • Uses exponential increase everywhere (in slow start and congestion avoidance)
  • Multiplicative decrease factor b = 0.125
  • Introduced by Tom Kelly of Cambridge

Information courtesy of Les Cottrell from the SLAC group at Stanford

highspeed tcp
Highspeed TCP
  • Behaves like Reno for small values of cwnd
  • Above a chosen value of cwnd (default 38) a more aggressive function is used
  • Uses a table to indicate by how much to increase cwnd when an ACK is received
  • Available with web100
  • Introduced by Sally Floyd

Information courtesy of Les Cottrell from the SLAC group at Stanford

binary increase control tcp bic tcp
Binary Increase Control TCP (BIC TCP)
  • Combine:
    • An additive increase used for large cwnd
    • A binary increase used for small cwnd
    • Developed by Injong Rhee at NC State University

Information courtesy of Les Cottrell from the SLAC group at Stanford

for more information
For More Information
  • Supercomputing 2004, Bandwidth Challenge
  • Scalable TCP
  • Highspeed TCP
  • Binary Increase Control (BIC) TCP
thank you
Thank you

John Hicks

Indiana University