Capwap Mailing List: Re: Issue 171: Pasi nits on binding spec

[Pasi.Eronen (Pasi.Eronen]

Pat Calhoun wrote:

> > Does this mean that e.g. all WTPs MUST support WMM? (since the AC
> > MUST always send the WMM information element) And MUST support WPA
> > forever (in addition to RSN)?
> 
> Well... We are 2007, and I'm not sure how much we need to care about
> hardware out there that is unable to support IEEE 802.11-2007. If
> there is ever a new IEEE standard for securing, then the list of IEs
> would have to change, but that would be post IEEE 802.11-2007
> anyhow. The CAPWAP specification could publish an updated set of
> rules of what IEs need to be present.

I can't find any mention of "WMM Information Element" in IEEE
802.11-2007 -- I assumed it's some extension that not everyone
implements?

BTW, how are you planning to update these rules without breaking
backwards compatibility?

<snip>
> Oh, I see. Well, that makes sense. Here is the new text:
> 
> <new text>
> 6.20.  IEEE 802.11 Update Station QoS
> [...]
>       0                   1                   2                   3
>       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 
> 8 9 0 1 2
>      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>      |   Radio ID    |                  MAC Address                  |
>      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>      |          MAC Address          |   DSCP Tag    | Reserved|8021p|
>      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> [...]
>    Reserved:   All implementations complying with this 
> protocol MUST set
>       to zero any bits that are reserved in the version of 
> the protocol
>       supported by that implementation.  Receivers MUST 
> ignore all bits
>       not defined for the version of the protocol they support.
> 
>    8021p:   The three bit 802.1p priority value to use if 
> packets are to
>       be IEEE 802.1p tagged.
> </new text>

Here DSCP Tag should be 6 bits, not 8.

<snip>
> > > > Section 6.20 and 6.22: "if packets are to be DSCP tagged" would
> > > > benefit of
> > > > clarifying what packets are meant (I guess it means CAPWAP Data 
> > > > packets sent from the WTP to the AC?).
> > > 
> > > New text:
> > > <new text>
> > > 6.20.  IEEE 802.11 Update Station QoS
> > > 
> > >    The IEEE 802.11 Update Station QoS message element is used 
> > >    to change
> > >    the Quality of Service policy on the WTP for a given station.
> > >    The
> > >    QoS tags included in this message element are to be applied to
> > >    packets received by the station.
> > 
> > By "packets received by the station", do you mean "packets 
> > sent by the
> > WTP to the station"? (In this case, including DSCP here is slightly
> > unexpected -- those packets aren't necessarily even IP?)
> 
> Hmmm... Should have read: "applied to packets received at the WTP from
> the station."

In this case, it seems both "Update Station QoS" and "WTP Quality of
Service" message elements apply to same packets -- how do they
interact?

How does the tagging work (or not work) if the 'C' bit in IEEE 802.11
Station Session Key message element is set?

I'm also slightly surprised to see the WTP modifying the contents of
IP packets here -- I thought it was acting as Layer 2 device for user
plane traffic (not making any assumptions about the Layer 3 protocol
carried in 802.3 frames). At the very least, the text should probably
say the DSCP Tag applies only to packets with certain values in the
802.3 Type field.

> > > [...]
> > > 6.22.  IEEE 802.11 WTP Quality of Service
> > > 
> > >    The IEEE 802.11 WTP Quality of Service message element value is
> > >    sent by the AC to the WTP to communicate quality of service
> > >    configuration information.  The QoS tag included in 
> this message
> > >    element are to be applied to packets received by the WTP from
> > >    station on a particular radio.
> > > </new text>
> > 
> > By "applied to packets received by the WTP from the station", do you
> > mean the tagging is applied to the headers received by the WTP, or to
> > the headers added by WTP for CAPWAP data tunneling?
> > (If it's the former, the comment above about DSCP applies)
> > 
> I am proposing adding the following sentence to both sections 6.20 and
> 6.22:
> 
> <new text>
>    Any tagging performed
>    by the WTP MUST be directly applied to the packets receive from the
>    station, as well as the CAPWAP tunnel, if the packets are 
>    tunneled to the AC.
> </new text>

The comment above about 'C' bit and DSCP Tag applies here as well...

<snip>
> > Well, some new WTPs might decide *not* to support WEP anymore --
> perhaps not yet, but five year from now..? (But if support of WEP is
> required, the document should say so)
> 
> Understood, but IEEE 802.11-2007 still requires the AP support it.

If I'm reading IEEE 802.11-2007, Section A.4.4.1 correctly, it
seems supporting WEP is optional...?

Best regards,
Pasi