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How to enable ShortGI for better 802.11n performance

Discussion in 'Tomato Firmware' started by benson, Dec 26, 2012.

  1. benson

    benson Serious Server Member

    How to enable ShortGI for better 802.11n performance? I can't find a option to select longGI and ShartGI
     
  2. Mangix

    Mangix Networkin' Nut Member

    Tools > System > type

    nvram set wl0_plcphdr=short
    nvram set wl1_plcphdr=short
    nvram commit

    edit: i should clarify that by default, preamble is long for b/g networks and short for n.
     
  3. benson

    benson Serious Server Member

    :) thanks, I try it.
     
  4. Mangix

    Mangix Networkin' Nut Member

    i edited my above post. the original will definitely not do anything.

    an extra note: I have not been able to figure out how to apply a short shotslot override instead of a long one. I assume it's short by default but I have no clue...
     
  5. benson

    benson Serious Server Member

    ShortGI(Short Guard Interval) is a standard of 802.11n, I think shortslot is another thing, it's not same.
    ShortGI can reduce latency from 0.8ms to 0.4ms, can lead higher network responsibility.
     
  6. Mangix

    Mangix Networkin' Nut Member

    my understanding is that the setting for a ShortGI is found under Advanced > Wireless > 802.11n Preamble

    The options there are "Off, Mixed, Greenfield, and GF-BRCM". Mixed is the default and I guess it allows both Greenfield and GF-BRCM at the same time. Greenfield being another name for a ShortGI.
     
  7. benson

    benson Serious Server Member

    802.11n Preamble is a 802.11n packet header type. Greenfield is the 802.11n standard packet header structure(Type), GF-BRCM is 802.11n draft version packet header structure(Type).
    ShortGI(Short Guard Interval) is the delay between every packet transmit.
     
  8. Mangix

    Mangix Networkin' Nut Member

    It's possible that it gets activated in N only mode. No clue.

    Part of the problem is that the Broadcom wireless drivers are not open source and as such without actually doing a packet sniff, it's hard to verify much.

    Although if a guard interval has to do with speed, it might be hard to even verify that.
     
  9. benson

    benson Serious Server Member

    thanks for your reply.
    hope new Broadcom wireless drivers can offer this function. ShortGI(Short Guard Interval) can be set to long|short|auto.
     

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