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QOS - DSL overhead value

Discussion in 'Tomato Firmware' started by alfag4, Dec 4, 2013.

  1. alfag4

    alfag4 Reformed Router Member

    i read some threads regards this option but i'm not sure if my settings are corrects.
    I have 1/20Mbps ADSL2 with the modem in bridge LLC/snap mode and the N66U in PPPoE so i set the QOS dsl overhead value in tomato to "40 - PPPoE LLC/SNAP" and for max bandwidth limit the link speed that in my case is 1004295/222236744 so 970/21700kbits. Speedtest give me an average speed of 0.84Mb/18.74Mb.
    This option could calculates the correct overhead for you without needs to insert the the real speed minus 15-30%.
    With these values all my class limit are incorrect because tomato calculates the limits from "max bandwith limit". For example: with FileXfer outbound limit to 100%, tomato calculate 21700Kbit=2712KB/s but my max download speed is about 2350KB/s=18.74Mb/s.
    Qos works properly with these settings?
  2. Porter

    Porter LI Guru Member

    Sorry, can't help you with the overhead. Seems like you've chosen the right value and a higher overhead value usually doesn't hurt as much as a too low value.

    I don't understand what you mean by Tomato calculating the wrong class limits. When you put in 840kbit in outbound direction and 18740kbit in inbound direction this might be a good starting point, since you work with the overhead calculation. You might want to deduce 5% from those values but I really can't see what you're problem is.
  3. alfag4

    alfag4 Reformed Router Member

    It's not really a problem. What i would say is that when you use the "dsl overhead" option you must put the dsl link speed in "max inbound/outbound", but is not the really max speed and tomato calculates the limits from these values.
    So for example, if i limit a class to max 512kbit the real limit is less because the overhead is not considered.
  4. Porter

    Porter LI Guru Member

    Yes, I know that the limits are not correct anymore. But the important part is that the underlying protocols are screwing the calculation. QoS might not be as accurate anymore if you look at the numbers but it is more accurate where it is even more crucial: not transfering more bandwidth than we actually have.

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