Prioritize ACK packets

Discussion in 'Tomato Firmware' started by RXP1, Aug 26, 2008.

  1. RXP1

    RXP1 Addicted to LI Member

    I've set my torrent server to the lowest priority via its MAC address. I was wondering if there is a way to enable priortise ACK packets for all the network except for the torrent server? Even though I set the rule I presume the ACK packets will still get a highest priority, even though the MAC address is lowest.
  2. rhester72

    rhester72 Network Guru Member

    This doesn't have as much value as it may appear, since only small (<128 bytes, I believe) ACK packets are prioritized. Torrent packets that ACK are larger and thus do not have the priority boost applied.

  3. yejun

    yejun Addicted to LI Member

    It should be prioritized, because the amount of ACK packets are directly proportional to the size of your downloaded data. Delayed ACK packets only cause slowed download rate and unnecessary retransmission, which leads to even more ACK packets. Unless your download link is also saturated, you may want to delay ACK to slow down download rate.

    To reduce ACK traffic, you can set a higher TcpAckFrequency in registry on a windows machine.
  4. RXP1

    RXP1 Addicted to LI Member

    I've found that not enabling ACK doesn't effect my download speed at all, it maxes it out at 100%. But I have renabled it for VoIP/Xbox. Wonder if it would be possible in a new firmware to say not to put ACK on high priority for certain MAC addresses.
  5. spliff

    spliff LI Guru Member

    You don't want to prioritize acks if you constantly leave a lot of torrents seeding such that they max out your upload. If prioritized the high amount of ACK traffic will affect other high priority traffic, IE web surfing. If you don't prioritize ACK traffic then your torrent download speeds will be affected. There is a workaround though.

    To solve this issue and get the best of both worlds (fast torrent uploads and downloads without affecting important traffic) do the following.

    1) Set your default traffic priority to low (instead of default=lowest)
    2) In QOS create an explicit rule for your torrent uploads. This means set source IP and port for your torrent client to lowest
    3) Uncheck prioritized ACKS

    The solves the problem because now your torrent downloads will fall into the default category of low, and your uploads (including the ACKS) will be lowest (all ACKS will be low unless explicitly specified like you did in 2 above). Your torrents will download fast, and your uploads can stay running all the time without affecting your torrent download speeds.
  6. rhester72

    rhester72 Network Guru Member

    Slowing down small ACKs is madness. It absolutely and directly impacts download speeds. If you don't believe this, you aren't saturating your uplink.

  7. spliff

    spliff LI Guru Member

    Thats why the traffic that is saturating your upstream (torrent uploads) should be set to lowest but your default traffic priority should be set above that. This way your download acks don't get delayed from being in the lowest class.
  8. rhester72

    rhester72 Network Guru Member

    I have yet to see any evidence whatsoever that torrent ACKs (and for that matter, *any* packet can contain an ACK - virtually all streaming protocols work in exactly the same manner) are inappropriately boosted by prioritizing ACKs in small packets only (which is what the checkbox does). That having been said, go with what works for you. =)

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