[orbit-user] Follow up on: RSSI per received packet using Atheros

[Rodney Berriman]

oops, found the prism2 header, in net80211/ieee80211_monitor.h

Still don't know why it doesn't appear in tcpdump.

Rodney

> thanks for your replies Kishore and Gautam.
>
>  
> We have tried to catch the RSSI in Prism2 header, having first ensured:
> /proc/sys/net/ath0/dev_type = 802     as per 
> http://madwifi.org/wiki/UserDocs/MonitorModeInterface
>
>  then run command:
>     tcpdump -i ath0 -vvv -s 0 -y PRISM_HEADER -e
>
>  Typical result for a ping request packet is:
>
> 23:10:44.580785 314us DA:00:0b:6b:0a:83:78 SA:00:0b:6b:0a:83:21 
> BSSID:02:0b:6b:0a:83:7e LLC, dsap SNAP (0xaa), ssap SNAP (0xaa), cmd 
> 0x03, IP (tos 0x0, ttl  64, id 0, offset 0, flags [DF], length: 84) 
> 192.168.200.109 > 192.168.200.126: icmp 64: echo request seq 5379
>
> tcpdump version info:
>    tcpdump version 3.8.3
>    libpcap version 0.9.4
>
> These are quite up to date, but I'm wondering if libpcap has the 
> necessary decoder for all the fields of prism2?
>
> There was no warning about libpcap being unable to decode, such as 
> does appear if I change the format to  804 "Atheros descriptors".
>
>
> Now looking through the madwifi source code to see if RSSI is hiding 
> in the binary format.
> Not seeing any reference to Prism2 header in the code, but maybe 
> IEEE802_11 RX stats is relevant.
> Is prism2 an extension of IEEE802_11 header?
>
> /* not all hardware provides this information for frames received */  
> (that might be significant!)
> struct ieee80211_rx_stats {
>   u32 mac_time;
>   s8 rssi;   /* what we want */
>   ...
>
> Any pointers most welcome,
>
> Rodney
>  
>
> Networks Systems Group
>
> NICTA, Sydney
>
>   
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