On Jan 10, 2019, at 10:17 AM, Jeija wrote:
>> 1) Would the link-layer header include any radio metadata? For 802.11,
>> there are various forms of radio metadata headers, such as the radiotap
>> header:
>>
>> http://www.radiotap.org
>>
>> If so, what would the format of the radio metadata be?
>
> I would suggest something similar to what the LoRa people did with LoRaTap:
> https://github.com/eriknl/LoRaTap
> For the uplink, except for version / padding / length of course, I don't
> think we need anything other than the uplink frequency (Sigfox uses a
> continuous uplink band) and an RSSI value.
> For the downlink we should again have frequency and RSSI, but maybe also some
> metadata (sequence number / device ID) about the corresponding uplink (Sigfox
> is an uplink-initiated protocol, i.e. downlinks are only transmitted after
> they have been requested by a corresponding uplink and their scrambling
> depends on the uplink metadata, something that is described in patent
> EP3259864A1).
> But I'm not sure whether the link-layer header is the correct place for this
> kind of information?
Where *else* would it go in a pcap file?
There *could* be additional metadata in the form of options in a pcapng file,
but there's no such option for pcap. 802.11 has multiple link-layer header
extensions for radio information, such as radiotap.
>> 2) The 2.2.2 "Implementation by Sigfox" section of the spec shows, on
>> page 14, a frame structure.
>>
>> In the captures, is the first byte of frame data (following the
>> radio metadata, if there is radio metadata, or at the beginning of the
>> packet, if there is no radio metadata), the first byte of the Preamble/Type?
>
> IMO the first byte of frame data should be the first byte of the "Type",
> since the "Preamble" is constant and just something that is used to detect
> the presence of a Sigfox uplink inside the uplink band and to synchronize the
> receiver.
So are you saying that the first byte of frame data should have the first 8
bits of the Type, with the next byte having 4 bits of Type and 4 bits of Flags?
> Thank you two for your work, I'd be very happy to see this being integrated
> into libpcap :) !
"Integrated into libpcap" or "integrated into the link-layer header types page
on tcpdump.org"?
If you're just specifying a link-layer header type, the key part is "integrated
into the link-layer header types page on tcpdump.org". Putting into pcap/dlt.h
and pcap-common.c just acknowledges the addition to the link-layer header type
page.
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