On 05/29/2020 12:06 AM, David Rowe wrote: > Hi Tomas, > Jeroen - I'd be interested to hear your thoughts and how your VHF packet > mode can map to this work ... I'm a just "the physical layer guy" :-) >
Actually it is pretty close. On the API side it provides an ethernet like layer so I use a TAP device instead of TUN. So just one layer below, this is mainly done to have a place to store a callsign as identification. (By accident the first packets our repeater transmitted were ipv6 router solicitations....) On the modem side it might map perfectly, or not.... I don't know what Tomas used to create 'packets'. Traditional packet systems use variable packet lenghts recognizable by some preample (ethernet) or flags (ax.25). The FreeDV modes all work on fix sized frames (which makes perfect sense if you are transmitting fixed size codec frames) and the VHF packet mode knows how to handle it. It gets chunks of data (6 or 8 bytes per frame and a few control bits) and re-assembles a packet if all frames are in. It does know how to use different sized chunks though: 6 (800XA), 8 (2400A/B) and in case of my own mode 6000 experiments 8 or 81. Basically it can be used on pretty much any thing that can provide a bunch of demodulated bits (mode 800XA with only 56 bits is pushing it though) at a time. It leaves the 'nasty' stuff like syncing, FEC to the modem. It just has a CRC per packet to make sure a frame is intact. Regards, Jeroen _______________________________________________ Freetel-codec2 mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/freetel-codec2
