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rates - bytes/sec - forgetting VLAN tag o/h?

Discussion in 'Tomato Firmware' started by RobNC, Jan 8, 2007.

  1. RobNC

    RobNC Network Guru Member

    I set up some QoS for VoIP. My provider told me that they're using G.711u so it should be using 64kbps payload rate (w/o overhead), so I figure 70kbps. If I set Tomato 1.02 to 68-70kbps on highest priority, set via IP address, I get choppy voice. If I set highest to 75-95kbps, the choppiness goes away.

    So, I got to thinking, could it be that the 5 queues (ignoring ABCDE) in tomato assume bytes/sec but fail to consider the VLAN tag overhead (4-bytes for 802.11p and 802.11q)? It is even more important for VoIP because of the small frames used (64B but I am not entirely sure; surely much much less than 1514B).

    Can anyone confirm this? If so, it might make more sense why I had to set the bits/sec so high. Also, if you turn off QoS, does that effectively not use 802.11p/802.11q (thus no extra 4-bytes overhead penalty)?

    I'm also not sure where the downstream QoS is considered ("shaped" via dropping ACKs), is it on the ingress WAN interface (w/o VLAN tag) or on the egress LAN interface (w/VLAN tag)? Similarly, not sure about upstream traffic, I assume it is shaped on the ingress LAN interface (so shouldn't the VLAN tag 4-byte overhead be considered)? If it shapes on the LAN interface (which has VLAN tag), then there might not be a way to correctly "reverse-engineer" the WAN shaping because the frame size wouldn't be known in advance of the shaping (if it truly shapes based on kbps). It is even more complex (if not impossible) if shaped based on packets/sec because of the vastly different sizes between max and min packet sizes.
  2. GeeTek

    GeeTek Guest

    I would go about VOIP QOS a bit differently. If no other traffic is to have more priority than VOIP, then assign VOIP 100% of your available bandwidth. It is a fixed protocol, and will use only what it needs, but at maximum priority. If other traffic is less important, put limits on that other traffic to ensure that it does not eat into the VOIP space.
  3. paped

    paped LI Guru Member

    I agree with Geetek set your voip as the only "Highest" priority entry (and move it to the first position or rather at the top of the list) then prioritise all other traffic from the "High" priority tag down. Voip should always have the highest priority above all else as it is a realtime app, where most data apps such as web browsing etc can normally deal with a bit of latency. Also for a G711 codec + IP headers you normally assume around 80kbps so any set-up using 68 to 70kbps probably would give choppy results, however by setting up voip on the highest tag with 100% traffic available if required (as explained above in this and Geetek's post) should sort any choppyness issues out.... Hope this helps....
  4. RobNC

    RobNC Network Guru Member

    Thanks, I did try this. Still getting choppy voice some of the time, so it's either the ISP or the VoIP provider (ViaTalk). May have to switch back to Vonage b/c at least Vonage the Tivo dial-in works (yeah I know it can be hacked but I haven't had time yet).
  5. heidnerd

    heidnerd LI Guru Member

    With Tivo, you could just use a Linksys USB NIC (USB200M) (see Tivo's web page) and connect the Tivo to the Internet without the phone. Works for me... Tivo may even have support for a Wifi combination...
  6. RobNC

    RobNC Network Guru Member

    I understand, but I'm using the DirecTivo HD10-250. No support for USB NICs or HMO, officially.

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