[Prism54-devel] RFC: wifi_modes.txt v0.1
Denis Vlasenko
vda at port.imtp.ilyichevsk.odessa.ua
Thu Mar 31 09:04:04 UTC 2005
On Wednesday 30 March 2005 00:55, Jean-Baptiste Note wrote:
> > Comments, additions, corrections, questions welcome.
> > Answers are sought too (grep for Q1 etc below).
>
> No answer to give, but some experience to share !
> > Q1: hostap transmits probes with ratevector where basic rates are flagged
> > (ORed with 0x80). Is this standard compliant?
>
> I don't know, but madwifi does this too with atheros cards. This seems
> logical, as you somehow have to flag the rates you require the client to
> support in order to connect to you.
This is a gray area. See the (somewhat long) thread pasted below my sig,
especially grep for '(since client does not specify basic rates)' in
Jouni Malinen post.
So, do we need to flag basic rates or not?
It will be cool if this will be cleared out.
> > Q2: hostap cards do not send ack for probe request. Packet dump suggests that
> > sender was expecting ack (or else why do we see retransmits?)
>
> Well i still don't know, but
>
> * prism54 does not send acks either
>
> * my first-gen apple aiport card (with linux driver) does the same in
> that it sends very fast four probe requests.
I was stupid. Probe req is bcast. Bcasts don't get ACKed.
> Wouldn't those be probes launched at different rates ? -- actually i'd
> love to be able to snoop the rate data of a received packet, but i don't
> know of any card which reports it correctly. I think that the softmac
> usb has this information somewhere in the received packet, alas, I can't
> pinpoint it (as i don't know either how to send packets at a fixed,
> rigid rate from any cards I have. Madwifi/atheros should be able to do
> this, but more testing is needed).
>
> > Q3: what are the matching rules for peer/peer basic/oper rates compatibility?
>
> > Q4: hostap use BSSID=mac|0x020000000000. Is this mandated by standard?
>
> Same for madwifi. Still don't know if that's standard.
>
> Thanks a lot for this document, it'll help me a lot :)
Send me additions, then :)
> Will you tackle lower-level things such as ATIM windows etc ? I guess,
> but am not sure, that host mode requires more complexity at higher
> levels (station management & al), but also at lower levels (this is what
> bothers me, i'm under the impression that hostap mode won't be easy with
> prism54u for this reason).
I will probably amend it as needed.
Promised thread is below.
--
vda
> I tried several pairs with the "iwpriv wlan0 SetRates" command but I don"t
> know how to find out what is working and what not. How do I find this out?
> I"m eager to get it working and report a success but it seems there is
> basic knowledge about wlan missing :-( (I"ve several years of linux
> experience but only a couple of days of wlan). Is there a way of letting
> ndiswrapper run and see which Rates it"s using?
I never used ndiswrapper.
As I said, debug=0xffff will report basic and oper rates for each AP seen.
After that, simply list those rates in your SetRates command:
iwpriv wlan0 SetRates "1,2,5,11 6,9,12"
^^^^^^^^ ^^^^^^
basic oper
--
vda
From: Marco Nierlich <mani at ac...>
Re: DWL-G650+ not working
2004-08-31 05:10
Denis Vlasenko wrote:
> > > Which version of driver?
> >
> > the log below was pf26, but the 0xfff in my followup post (10:38am) was
>
> ^^^^^
> must be 0xffff
>
done
> [...]
> As I said, debug=0xffff will report basic and oper rates for each AP seen.
> After that, simply list those rates in your SetRates command:
>
> iwpriv wlan0 SetRates "1,2,5,11 6,9,12"
> ^^^^^^^^ ^^^^^^
> basic oper
iwpriv wlan0 SetRates "2,5,11 6,9,12,18,24"
dhcpcd wlan0
success :-)
Thanks a lot!
Hope that I can one day contribute as well!
Marco
From: Andreas Mohr <andim2 at us...>
Re: DWL-G650+ not working
2004-08-31 06:01
Hi,
On Tue, Aug 31, 2004 at 02:09:43PM +0200, Marco Nierlich wrote:
> iwpriv wlan0 SetRates "2,5,11 6,9,12,18,24"
> dhcpcd wlan0
>
> success :-)
>
> Thanks a lot!
> Hope that I can one day contribute as well!
Ah, no wonder it didn"t work:
Aug 31 10:21:05 pingu new ratevector: 82 84 8b 8c 92 96 98 a4 ac b0 c8 e0 ec
That means that our driver set *all* rates as basic rates (bit 0x80).
I guess we really, really shouldn"t do that...
But OTOH I"m still not quite sure why the AP has some trouble with that:
the peer has to support all rates that the AP requests (basic rates),
but who requires that not all rates announced by the peer are basic rates?
Denis: we should probably restrict our basic rates announcement to
1, 2, 5.5, 11, right?
Andreas Mohr
From: Denis Vlasenko <vda at po...>
Re: DWL-G650+ not working
2004-08-31 08:26
On Tuesday 31 August 2004 16:01, Andreas Mohr wrote:
> Hi,
>
> On Tue, Aug 31, 2004 at 02:09:43PM +0200, Marco Nierlich wrote:
> > iwpriv wlan0 SetRates "2,5,11 6,9,12,18,24"
> > dhcpcd wlan0
> >
> > success :-)
> >
> > Thanks a lot!
> > Hope that I can one day contribute as well!
>
> Ah, no wonder it didn"t work:
> Aug 31 10:21:05 pingu new ratevector: 82 84 8b 8c 92 96 98 a4 ac b0 c8 e0 ec
>
> That means that our driver set *all* rates as basic rates (bit 0x80).
> I guess we really, really shouldn"t do that...
> But OTOH I"m still not quite sure why the AP has some trouble with that:
> the peer has to support all rates that the AP requests (basic rates),
> but who requires that not all rates announced by the peer are basic rates?
Because AP"s software may be buggy as well.
> Denis: we should probably restrict our basic rates announcement to
> 1, 2, 5.5, 11, right?
No. We should honour whatever user sets via SetRates.
If user sets rate with "iwconfig rate", we are basically free
to mark all, some, or only lowest rate (1Mbit) as basic.
I think Wireless Extensions simply have no definitive rules for this.
(CCing Jean and Jouni to let them comment on this).
--
vda
From: Marco Nierlich <mani at ac...>
Re: DWL-G650+ not working
2004-08-31 08:53
Denis Vlasenko wrote:
> On Tuesday 31 August 2004 16:01, Andreas Mohr wrote:
> > Hi,
> >
> > On Tue, Aug 31, 2004 at 02:09:43PM +0200, Marco Nierlich wrote:
> > > iwpriv wlan0 SetRates "2,5,11 6,9,12,18,24"
> > > dhcpcd wlan0
> > >
> > > success :-)
> > >
> > > Thanks a lot!
> > > Hope that I can one day contribute as well!
> >
> > Ah, no wonder it didn"t work:
> > Aug 31 10:21:05 pingu new ratevector: 82 84 8b 8c 92 96 98 a4 ac b0 c8 e0
> > ec
> >
> > That means that our driver set *all* rates as basic rates (bit 0x80).
> > I guess we really, really shouldn"t do that...
> > But OTOH I"m still not quite sure why the AP has some trouble with that:
> > the peer has to support all rates that the AP requests (basic rates),
> > but who requires that not all rates announced by the peer are basic
> > rates?
>
Is there a reason why SETRATES is not in the startup script? I"d be glad to
submit a patch.
Marco
From: Jean Tourrilhes <jt at bo...>
Re: DWL-G650+ not working
2004-08-31 10:22
On Tue, Aug 31, 2004 at 06:25:24PM +0300, Denis Vlasenko wrote:
> On Tuesday 31 August 2004 16:01, Andreas Mohr wrote:
> > Hi,
> >
> > On Tue, Aug 31, 2004 at 02:09:43PM +0200, Marco Nierlich wrote:
> > > iwpriv wlan0 SetRates "2,5,11 6,9,12,18,24"
> > > dhcpcd wlan0
> > >
> > > success :-)
> > >
> > > Thanks a lot!
> > > Hope that I can one day contribute as well!
> >
> > Ah, no wonder it didn"t work:
> > Aug 31 10:21:05 pingu new ratevector: 82 84 8b 8c 92 96 98 a4 ac b0 c8 e0 ec
> >
> > That means that our driver set *all* rates as basic rates (bit 0x80).
> > I guess we really, really shouldn"t do that...
> > But OTOH I"m still not quite sure why the AP has some trouble with that:
> > the peer has to support all rates that the AP requests (basic rates),
> > but who requires that not all rates announced by the peer are basic rates?
>
> Because AP"s software may be buggy as well.
How true ;-)
> > Denis: we should probably restrict our basic rates announcement to
> > 1, 2, 5.5, 11, right?
>
> No. We should honour whatever user sets via SetRates.
SetRate is an "advanced" command, it will be only used if the
user wants it (i.e. not in default scripts), therefore it"s OK to
allow the user to shoot himself in the foot.
> If user sets rate with "iwconfig rate", we are basically free
> to mark all, some, or only lowest rate (1Mbit) as basic.
> I think Wireless Extensions simply have no definitive rules for this.
> (CCing Jean and Jouni to let them comment on this).
This is the "user-friendly" command, can be used by scripts,
therefore here we want to make sure the user can"t do stupid
things. The command doesn"t say anything about the basic rate, so just
make sure you use something sensible. It only set the transmit rate
for unicast packet. With auto, it should use some rates up the the
value, with fixed only this value. Obviously, you want to make sure
things always work, so filter out rates as needed.
> vda
Jean
From: Jean Tourrilhes <jt at bo...>
Re: DWL-G650+ not working
2004-08-31 10:59
On Tue, Aug 31, 2004 at 08:43:07PM +0300, Denis Vlasenko wrote:
> Which rates should be "basic rates" if user says "iwconfig rate N auto" ?
Not specified, so something that works and is safe. I guess it
would not make sense to have basic rate greater than N.
> vda
Jean
From: Denis Vlasenko <vda at po...>
Re: DWL-G650+ not working
2004-08-31 12:38
> > Which rates should be "basic rates" if user says "iwconfig rate N auto" ?
>
> Not specified, so something that works and is safe. I guess it
> would not make sense to have basic rate greater than N.
Of course. But IIRC in this case card was programmed with "rate 54M auto"
and *all* rates were flagged as basic. Yet, AP rejected assoc...
We *cant* figure out what is "something that works" in real 11g life.
--
vda
From: Jean Tourrilhes <jt at bo...>
Re: DWL-G650+ not working
2004-08-31 13:39
On Tue, Aug 31, 2004 at 10:37:50PM +0300, Denis Vlasenko wrote:
> On Tuesday 31 August 2004 20:59, Jean Tourrilhes wrote:
>
> > > Which rates should be "basic rates" if user says "iwconfig rate N auto" ?
> >
> > Not specified, so something that works and is safe. I guess it
> > would not make sense to have basic rate greater than N.
>
> Of course. But IIRC in this case card was programmed with "rate 54M auto"
> and *all* rates were flagged as basic. Yet, AP rejected assoc...
>
> We *cant* figure out what is "something that works" in real 11g life.
If you can"t figure that out, how do you expect random joe
user to figure it out ? You are in the 1% that grok 802.11, most users
don"t even know that basic rate exist and what it means.
I guess that you should pick a default that is "conservative",
and people that really want the last drop of performance can tweak the
driver as needed.
> vda
Jean
From: Jouni Malinen <jkmaline at cc...>.hut.fi>
Re: DWL-G650+ not working
2004-08-31 19:04
On Tue, Aug 31, 2004 at 06:25:24PM +0300, Denis Vlasenko wrote:
> On Tuesday 31 August 2004 16:01, Andreas Mohr wrote:
> > Aug 31 10:21:05 pingu new ratevector: 82 84 8b 8c 92 96 98 a4 ac b0 c8 e0 ec
> > That means that our driver set *all* rates as basic rates (bit 0x80).
> > I guess we really, really shouldn"t do that...
> > But OTOH I"m still not quite sure why the AP has some trouble with that:
> > the peer has to support all rates that the AP requests (basic rates),
> > but who requires that not all rates announced by the peer are basic rates?
I"m somewhat confused about the case here (probably because I have not
seen beginning of this thread).. Is that ratevector from AP or client?
If it is from AP, it is somewhat restrictive, if it is from client, it
is incorrect (since client does not specify basic rates).
> > Denis: we should probably restrict our basic rates announcement to
> > 1, 2, 5.5, 11, right?
>
> No. We should honour whatever user sets via SetRates.
>
> If user sets rate with "iwconfig rate", we are basically free
> to mark all, some, or only lowest rate (1Mbit) as basic.
> I think Wireless Extensions simply have no definitive rules for this.
> (CCing Jean and Jouni to let them comment on this).
There is no configuration for basic rates in the current Linux wireless
extensions. For client case, it should not matter since client (well, I
mean a client that associates with an AP, not IBSS) does not need to
select which rates are in the basic rate set. I would be prepared to say
that client (to AP) does not need any rate configruation at all since it
can just follow what rates (and modulation) AP is advertising as
supported and then let TX rate control take care of eliminating rates
that do not work well.
Configuring supported and basic rate sets for an AP or the STA that
creates an IBSS is more complex. However, even for this, it is usually
enough to limit to some basic configurations. In most cases, I would
include all standard IEEE 802.11b, .11g, .11a rates that the STA
supports in supported rate set and use one of the follow basic rate set:
1, 2 Mbps
1, 2, 5.5, 11 Mbps
1, 2, 5.5, 11, 6, 12, 24 Mbps
6, 12, 24 Mbps
Of course, the configuration could be made fancier, but I don"t see much
use for that apart from some special test cases.
--
Jouni Malinen PGP id EFC895FA
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