RE: Setting the appropriate MTU

From: Julien Godard ([email protected])
Date: Tue Feb 15 2000 - 10:53:28 EST

  • Next message: Davenport, David M (CRD): "RE: Setting the appropriate MTU"

    Oups ! Yes, correct !
    I completelly forgot to look at the bandwidth. I am too use to run test with
    x Mbps...

    > -----Original Message-----
    > From: Johnson, Gregory LCDR [SMTP:[email protected]]
    > Sent: Tuesday, February 15, 2000 3:39 PM
    > To: Godard, Julien [HAL02:HM90:EXCH]; 'Testasecca, Mariano'
    > Cc: '[email protected]'
    > Subject: RE: Setting the appropriate MTU
    >
    > Bigger is not better for slow networks. For a link speed of 4kbps you will
    > need to use much smaller MTU sizes since the transmission time for a
    > packet
    > gets too long otherwise. It will also depend upon what the latency is in
    > the
    > link because the total transmission time for a packet is a function of the
    > size and delay. For a typical GEO link, I would expect that you have
    > anywhere up to 600ms depending upon what kind of FEC and interleaving is
    > done on the link. I have found for Inmarsat-M/Mini-M type links (2.4 kbps)
    > that an MTU size of 500 works well. You also need to adjust the initial
    > RTO
    > value larger (the default is 3 secs, try 5 secs). If you don't do this,
    > you
    > will suffer a lot of timeouts and retransmissions. I'm not that familiar
    > with the protocol Citrix uses, but with only 4kbps of bandwidth, you also
    > don't want to run multiple simultaneous connections across your link as
    > one
    > connection will probably saturate the link.
    >
    >
    > -Greg
    >
    > LCDR Gregory W. Johnson
    > Ass't Prof. Electrical Engineering
    >
    > USCG Academy
    > New London CT
    >
    > 860-444-8683
    >
    > -----Original Message-----
    > From: Julien Godard [mailto:[email protected]]
    > Sent: Tuesday, February 15, 2000 4:59 AM
    > To: 'Testasecca, Mariano'
    > Cc: '[email protected]'
    > Subject: RE: Setting the appropiate MTU
    >
    >
    >
    > for performance, the bigger the better !
    > But it may depend also on your network because you may want to avoid
    > fragmentation.
    > You can test your MTU with some free tools such as easyMTU
    > http://members.tripod.com/~EasyMTU/ <http://members.tripod.com/~EasyMTU/>
    >
    > For example if you use ethernet link, the MTU is 1500, leading to 1448
    > bytes
    > of data in each segment (20 IP + 20 TCP + 12 TCP timestamp option + 1448
    > data). If your router support this size without fragmentation, it's fine !
    >
    > -----Original Message-----
    > From: Testasecca, Mariano [SMTP:[email protected]]
    > Sent: Monday, February 14, 2000 7:49 PM
    > To: '[email protected]'
    > Subject: Setting the appropiate MTU
    >
    >
    > What MTU value would be appropiate for Windows 95/98 terminals
    > working as a
    > Windows NT 4.0 running Citrix MetaFrame under
    > a satellite link of a VSAT that provides 4kbps of bandwidth?
    >
    > Thanks to all.
    >
    > Mariano Testasecca
    > SIEMENS S.A.
    > Divisi�n Electromedicina
    > Servicios de Salud - SHS
    > Bolivar 177 1� Piso
    > *+54-11-4340-8400 int. 2796
    > * mailto:[email protected]
    > <mailto:[email protected]>
    >
    >
    >
    >
    >
    >
    >



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