• I was looking at a wireshark capture and noticed that all of the management frames I was seiing (beacon, probe request, probe response, association request, association response, authentication, and deauthentication) and the ACK control frame all have the ToDS and from FromDS bits set to 0. Is it only data frames that utilize the ToDS and from FromDS bits?

  • By (Deleted User)

    Yes, only data frames. Think about what these bits tell us: either the frame came from the distribution system (FromDS) or they are destined to the distribution system (ToDS). Management and Control frames are for wireless peers (to manage and control the wireless medium) only, so they never come from the DS and they never go to the DS.

  • Thanks.

    I always looked at the ToDS = 1 as meaning going to an AP and the FromDS = 1 as meaning coming from an AP so you can see my confusion since probe requests, association requests, and authentication requests all go to an AP and beacons, probe responses, association responses, and deauthentications all come from an AP. I guess I shouldn't look at it that way. I should look at it as going to and coming from the DS.

    However, when an ACK crosses a wireless distribution system (WDS) it's on the WDS but the ToDS and from FromDS bits still set to 0. Is this an exception to the rule?

  • I guess I stumped everyone!

  • Hardly.

    We just hoped you'd spend a minute and look it up yourself.


    If you had a 100% reliable and consistent Packet analyzer, you could just trust it (ha) to always decode it all correctly. Then just pay attention to the "logical addresses", instead of the actual address fields.

  • By (Deleted User)

    According to [url=]@matthewgast[/url] on twitter:

    [quote]802.11-2007 clause - ToDS and FromDS are only set on frames of type Data. The distribution system is like a bridging engine that forwards frames - ACKs are not independent frames to STAs.[/quote]

    If you're on Twitter, and you're not following Matthew Gast, you should follow Matthew Gast on Twitter.

  • By (Deleted User)

    If Gast's comment is not clear, an 802.11 ACK is a wireless frame to acknowledge a previous wireless frame that needs acknowledgment. 802.11 ACKs never go to or come from the distribution system because they are only used by wireless peers.

    802.11 ACKs are not the same as TCP ACKs. A TCP ACK would be an 802.11 data frame.

  • Thanks for all the responses. I'm still trying to wrap my mind around this.

    @Marcus, You said [b]"802.11 ACKs never go to or come from the distribution system because they are only used by wireless peers."[/b] However, when an 802.11 ACK crosses a wireless distribution system (from one AP to another AP that are bridged) it's crossing the DS (granted a wireless DS) which seems to contradict your statement. What am I not understanding? I'm thinking I might not have a good grasp on what a distirbution system is. Is it that non-data frames don't ever use the ToDS and FromDS bits even if they cross a DS? Again, thanks for sticking with me, sometimes I can be a little slow on the uptake.

    @wlanman, I did try to find the answer myself, however, I was unable to do so, that's why I posted the question here. This is a forum where people post questions and have discussions. If your goal is to to discourage people from asking questions then keep making snide comments without providing any helpful input.

  • Thanks for the nugget of knowledge!

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