IEEE 802.11 Wireless Multimedia Extension (WME) and raw sockets

[Sam Leffler]

Geir Egeland wrote:
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
> 
> Hi,
> I've been playing around with WME to test various network performance,
> and come across a problem that I can't quite understand.
> I have an application that generates traffic with various TOS
> (BACKGROUND, BEST EFFORT, VOICE, VIDEO). It uses raw sockets to transmit
> the IP packets. This all works well if ip->ip_len is less than 192
> bytes. If ip_>ip_len is larger than 192, the call to ieee80211_classify
> (/usr/src/sys/net80211/ieee80211_output.c) will classify the packet as
> "BEST EFFORT" no matter what value my application set the TOS  field as.
> 
> Debugging ieee80211_classify, I see that both ip->ip_tos and ip->ip_len
> are set to zero when a I send a packet with  ip->ip_len larger than 192
> bytes.
> Sniffing the network, I can see my packets have the correct TOS and
> length, but they don't get the correct WME classification.
> 
> 
> - -------------ieee80211_output.c(iee80211_classify)------------
>         if (eh->ether_type == htons(ETHERTYPE_IP)) {
>                 const struct ip *ip = (struct ip *)
>                         (mtod(m, u_int8_t *) + sizeof (*eh));
>                 /*
>                  * IP frame, map the TOS field.
>                  */
> //added by myself
> 	printf("IP_TOS: %d, IP_LEN: %d\n",ip->ip_tos,ntohl(ip->ip_len));
> //end
>                 switch (ip->ip_tos) {
>                 case 0x08:
>                 case 0x20:
>                         d_wme_ac = WME_AC_BK;   /* background */
>                         break;
>                 case 0x28:
>                 case 0xa0:
>                         d_wme_ac = WME_AC_VI;   /* video */
>                         break;
>                 case 0x30:                      /* voice */
>                 case 0xe0:
>                 case 0x88:                      /* XXX UPSD */
>                 case 0xb8:
>                         d_wme_ac = WME_AC_VO;
>                         break;
>                 default:
>                         d_wme_ac = WME_AC_BE;
>                         break;
>                 }
> 
> - -----------------------------------------------------
> 
> When I use SOCK_DGRAM socket instead of raw, everything works fine.
> 
> I use FreeBSD 6.0-STABLE and my wireless NIC uses an atheros chipset.
> 
> Has anyone got an idea what is going on ?

I'll check but the raw socket path must not have the ip header in the 
expected spot in the mbuf.  Most of my testing has been done with a 
modified version of netperf that slaps a TOS on the socket based on a 
command line argument so only UDP and TCP (not raw) traffic.

Ideally the 802.11 layer should not be doing classification; packets 
should be tagged and the 802.11 layer then does the mapping according to 
the standard.  Groveling around inside packets to extract stuff like 
this is evil.

	Sam