Bandwidth affected by latency

Discussion in 'Cisco' started by Frank, Nov 14, 2005.

  1. Frank

    Frank Guest

    We have a VPN tunnel to another company and use it to move large files
    (20-100M). We are only able to achieve ~250kByte transfer speeds. The
    ping-time is ~250ms. We are using a 9M partial DS3 with a PIX 525 and the
    receive site has 100M burst capability (unsure as to the equipment on the rx
    end).

    Yes, I have tried adjusting the RWIN during testing. No, the application is
    not able to create multiple send threads/streams. Is there a calculation to
    verify the transfer speed and factor the latency? What else could we look
    into to try and improve the tunnel speed?
     
    Frank, Nov 14, 2005
    #1
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  2. ;We have a VPN tunnel to another company and use it to move large files
    ;(20-100M). We are only able to achieve ~250kByte transfer speeds. The
    ;ping-time is ~250ms. We are using a 9M partial DS3 with a PIX 525 and the
    ;receive site has 100M burst capability (unsure as to the equipment on the rx
    ;end).

    :Yes, I have tried adjusting the RWIN during testing. No, the application is
    :not able to create multiple send threads/streams. Is there a calculation to
    :verify the transfer speed and factor the latency? What else could we look
    :into to try and improve the tunnel speed?

    I suggest you try ttcp, or better yet, netperf
    http://www.netperf.org/netperf/NetperfPage.html
     
    Walter Roberson, Nov 14, 2005
    #2
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  3. Frank

    Igor Mamuzic Guest

    Frank,

    Do you have any packet drops or maybe even high cpu
    utilization on your routers?
    Packet drops not counted as various types of frame errors (CRC, etc.) are
    mostly caused by overfilled queues.

    Please post 'show int' outputs of two interfaces that are making one of your
    VPN connections with poor performances...

    B.R.
    Igor
     
    Igor Mamuzic, Nov 15, 2005
    #3
  4. Frank

    Sam Wilson Guest

    I'm a novice in this area but for 250KBps (about 2Mbps) with a 250ms
    RTT is consistent with 64KB buffer sizes. To fill 9Mbps with a 250ms
    RTT you need to get your buffers up to about 280KB - 256KB might be OK.
    See Brian Tierney's TCP tuning pages at
    <http://www-didc.lbl.gov/TCP-tuning/> for an explanation.

    Sam
     
    Sam Wilson, Nov 15, 2005
    #4
  5. Frank

    thrill5 Guest

    Google "long fat networks" for more info high bandwidth, high latency
    networks.

    Scott
     
    thrill5, Nov 23, 2005
    #5
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