Two small problems with libpcap

Patrick McHardy kaber at
Wed Nov 24 12:55:36 UTC 2010

On 24.11.2010 13:50, Patrick McHardy wrote:
> 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
>>         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 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

One more thing - for good measure we should also somehow indicate
whether/which half slots are used, the slot number alone is not
enough for that.

> 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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