[Prism54-devel] RFC: wifi_modes.txt v0.1

[Jean-Baptiste Note]

Hello Denis,

> Comments, additions, corrections, questions welcome.
> Answers are sought too (grep for Q1 etc below).

No answer to give, but some experience to share !

> Info is collected from 802.11 .pdf manuals
> and packet dumps of wireless traffic of hosts
> with Prism2.5 802.11b PCI cards (hostap driver).

> ============================================================
> IBSS_SCAN (initialization of ad-hoc mode)
> -----------------------------------------
> Host is sending probe requests with desired ESSID and supported rates,
> and/or scanning for IBSS beacons from another peer.
> BSSID is obtained from probe responses or is randomly generated
> if no response was heard in ~0.5 sec, thus forming new IBSS cell.
> Then host goes into IBSS_PEER mode.
> PEER          PEER
> Probe Request --->
> <-- Probe Response
> (ack)------------>
>
> 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.

> 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.

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 :)

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).

JB

-- 
Jean-Baptiste Note
+33 (0)6 83 03 42 38
jean-baptiste.note at wanadoo.fr