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Thread: MTU with PPPoA

  1. #1
    UKOUser Guest

    Default MTU with PPPoA

    My NetGear router came with a default MTU of 1458 which worked fine, but soon I'm switching to UKOnline and during their setup guides they recommend I have my MTU set to 1500 which is apparently the max? and best.

    I changed it to 1500 and don't notice much difference, everything works anyway.. the only problem I have is with reading this article on wikipedia: http://en.wikipedia.org/wiki/Maximum..._of_MTU_tuning


    Now I'm far from an expert, but I want to have the optimum connection when it comes to gaming. This article seems to say that an MTU of 1478 (I think?) is the best for PPPoA connections?

    Could anyone shed some light on this? Thanks in advance for your time!

  2. #2

    Default

    You should get a small increase in throughput by using a MTU of 1478, rather than the maximum 1500 bytes, however I don't think there would be any appreciable benefit for gaming, as latency is important for gaming rather than speed.

    The small gain in throughput is due to ADSL using fixed size (53 byte) ATM cells to carry data. With the additonally required headers, a 1478 IP packet exactly fits 31 ATM cells, whereas a 1500 byte packet uses part of an additional ATM cell, and as ATM cells are fixed at 53 bytes, the remainder of the extra cell is filled by (wasted) padding bytes. 1478 is about 1.5% more efficient than 1500.
    Last edited by Mel; 06-06-2009 at 08:00 PM.

  3. #3
    Join Date
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    Default

    I think Mel has explained it best already, but basically latency boils down to whether you want to push more data through your pipe (bigger packets) or less (smaller packets), with the latter being good for gaming and the former being better for downloads. Generally speaking if your broadband works fine then I wouldn't recommend fiddling with the MTU unless you know what you're doing.
    Mark 'Winter' Jackson
    Editor-in-Chief - ISPreview.co.uk

  4. #4
    Unregistered Guest

    Default

    Thank you both very much, I've since changed my MTU to 1478, although I haven't noticed a change in latency or download rate, I'm going to leave it there since it's most efficient.

    I'm curious why you say it wouldn't affect latency though, surely if more data is being sent at any one time, more is getting out the way faster so instead of being [data][data][data] it would be [datadata][datadata] etc?

  5. #5
    UKOUser Guest

    Default

    That was me by the way... I really should just register..

  6. #6
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    Best way to find out the best MTU for your connection (they are all different) is to ping something ont he internet for example a games server you use etc.

    ping [IP of server] -f -l [size of packet]

    When the packet is too big then it will respond with unable to send etc.
    Unlimited-dsl what a ISP.

    Quote Originally Posted by unlimited-dsl View Post

    so if this hasnt been done, not my problem

    Regards,

    Darren

  7. #7

    Default

    With windows the -l parameter specifies the number of bytes of data to be transmitted in the ping packet, and excludes the 28 byte packet header, so the packet size sent is the value specified after the "-l" + 28. The maximum packet size would also be limited by the current MTU set on the router.

  8. #8
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    Well, I'm using 1478 now, thanks everyone!

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