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MAC Retransmission / WMM Retry Count

Discussion in 'Tomato Firmware' started by wizziwig, Apr 1, 2014.

  1. wizziwig

    wizziwig Reformed Router Member

    Does Tomato have any options similar to dd-wrt for setting the retry count for failed wifi packets?

    From dd-wrt advanced wifi-screen:


    I think you can also set this via "iwconfig eth0 retry" on most network cards but I'm not sure if that's possible on a Tomato router.

    I need this to improve local LAN UDP traffic reliability because UDP does not have automatic re-transmission like TCP. I assume the default Tomato short/long retry counts are just 7/4?
  2. Marcel Tunks

    Marcel Tunks Networkin' Nut Member

    Why are you having so many failed transmissions? Wireless problem?
  3. wizziwig

    wizziwig Reformed Router Member

    It's not a lot of dropped packets. Much less than 1%. But even a single dropped packet means lost data when dealing with UDP. This could result in video glitch or audio drop-out depending on what application you're using.

    You can check your own setup for dropped UDP packets using iperf. Just let it run long enough and you'll probably encounter a few, especially further out from router. I usually test for about 15-30 minutes.

    For example, this would simulate an RTP video stream:

    Run receiving server on wireless machine:

    iperf -s -u -l 1328

    Run sending client on wired ethernet machine:

    iperf -c -u -b 20m -t 900 -l 1328

    Replace the ip address with that of your server. You can also adjust the "20m" to change sending speed in mbits/sec and "900" for number of seconds to test. It will report results after test completes. 1 out-of-order packet is normal.

    For me, raising the retry counts slightly reduces the dropped packets to a point where I only see them at extreme distances with 5Ghz 150Mbps link 802.11n. With 802.11ac, there are usually even less dropped packets. It's a nice dd-wrt feature that seems to be missing in Tomato.

    Maybe there is a way to set it from telnet console?
    Last edited: Apr 1, 2014
  4. wizziwig

    wizziwig Reformed Router Member

    Figured out the right driver variables for my broadcom AC66U clone by digging through the dd-wrt source code.

    Either from telnet or Tools->System Commands :

    nvram set wl_wme_txp_bk="7 3 4 2 0"
    nvram set wl_wme_txp_be="7 3 4 2 0"
    nvram set wl_wme_txp_vi="7 3 4 2 0"
    nvram set wl_wme_txp_vo="7 3 4 2 0"
    sleep 2
    nvram commit
    sleep 10
    "7 3 4 2 0" are the default values. Just replace with whatever retry counts you need. I think 15 is the max retry for both short and long packets. No more dropped UDP packets for me. :D

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