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Packet Mode Questions
#8
(02-01-2021, 06:17 AM)akbat Wrote: Wait a second, I've been assuming that frames are packed into superframes as they get TXed and a superframe gets unpacked into frames on the RX end.
Is the process actually that we put some data into a superframe first, then split it up into frames for TXing? And the RX side would re-combine the frames into a superframe to recover the data?

That was an incorrect assumption.  Start by understanding the physical layer and the data link layer.  All M17 frames start with an 8-symbol sync word followed by 184 symbols.  This is true for all M17 frame types.

The M17 frame is unpacked into 368 bits, which are FEC encoded.  The sync word used indicates the M17 frame type and FEC coding used.  The packet sync word indicates that the frame is 7/8 punctured, has 25 data bytes and a 6-bit frame/byte count field.

The M17 packet protocol is split between data link layer (convolutional coding of the packet frame, frame counter, puncturing) and the application layer (construction of packet superframe and splitting of superframe into M17 data link layer packet frames).  Packet data gets packed into a superframe consisting of the type, packet data, CRC.  (Raw frames omit the data type information.) This is then split across data link layer frames.

The intention is that raw packet frames can allow a drop-in replacement for other packet protocols, and is what is being used for testing APRS over M17 today.  The encapsulated version is intended to be used to construct more complex network protocols, such as IP, 6LoWPAN, etc.
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Messages In This Thread
Packet Mode Questions - by akbat - 01-17-2021, 03:54 AM
RE: Packet Mode Questions - by SP5WWP - 01-23-2021, 06:07 PM
RE: Packet Mode Questions - by WX9O - 01-23-2021, 06:21 PM
RE: Packet Mode Questions - by WX9O - 01-24-2021, 10:42 PM
RE: Packet Mode Questions - by akbat - 01-26-2021, 09:55 PM
RE: Packet Mode Questions - by WX9O - 01-29-2021, 01:55 AM
RE: Packet Mode Questions - by akbat - 02-01-2021, 06:17 AM
RE: Packet Mode Questions - by WX9O - 02-01-2021, 04:25 PM

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