Two small problems with libpcap

Patrick McHardy kaber at trash.net
Wed Nov 24 12:50:29 UTC 2010


On 23.11.2010 23:32, Erik Tews wrote:
> Hi
> 
> I spotted two small problems with libpcap:
> 
>       * Preables for received PP frames are missing, the dedected.org
>         tools used to include the preamble as well. This can easily be
>         fixed by adding a default preamble if the kernel doesn't report
>         the preamble to the userspace.

I guess the kernel should report it, at least with double simplex
bearers the sender can't be determined based on the slot number.

>       * The slottime wraps around at 2^12 and not at 2^11 as it used to
>         wrap around with the dedected.org tools. I am not sure about the
>         best solution here, one could also use the full 16 bits for the
>         time which are available in the header.

I'm not sure what you're referring to here. The slot numbers are in
the range of 0-23.

Generally I think the header format should be revamped:

- we don't need the fake ethernet addresses
- the preamble should use 5 bytes for the case of a prolonged
  preamble
- the RSSI shouldn't use the raw COA values but defined units
- the multiframe number should be added
- the RF-band and/or specific frequency should be added. Using
  the RF-band is probably the more flexible way.
- drift for received packets could be added

additionally we could optionally ignore S-field errors in the driver
and indicate them in the frame header.

The easiest way to make these changes is probably to add a new
link type for the new header and have wireshark etc. deal with
that.




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