On 25/03/18 06:25, Bruce Perens wrote: > FreeDV voice packets are around 7 bytes per 40 milliseconds. Even a > single IPV6 /address /is twice the size, not to mention the rest of the > header. So, realistic expectations are called for. Header compression is > helpful. Retransmission of a TCP packet could easily be a 1500 or more > byte repeat, taking most of a second. The best mix of FEC to reduce > repeats while minimizing overhead is still open for your research.
Actually, I have been looking at how 6LoWPAN does things. In particular, I've been working with OpenThread at work, and considered rejigging that to work within AX.25 UI frames which could be transmitted with existing AX.25 hardware for FM, or utilise the FreeDV modem for SSB. 6LoWPAN ordinarily runs over IEEE 802.15.4. There, they have a 128-byte limit on link-layer frames, and a radio network of nodes where not all nodes can directly communicate. For nodes within the mesh, they actually use a shortened address to abbreviate the IP address to help compress the header down, and the protocols typically used over 6LoWPAN are typically geared to keep the packet size down (e.g. CoAP instead of HTTP). If you do send a big packet, it gets fragmented. I don't think there's repetition of a single frame within that segment, so it'd be up to upper layers to re-send the lot. Forward erasure coding would help a lot there as the probability of us losing a packet is so much higher. Thread is officially supposed to work over 2.4GHz, but there's nothing to suggest it couldn't work on HF. We just have to do our own modem to replace 802.15.4, and rejig the crypto so that shared keys are used to authenticate (a message integrity code) instead of encrypt. In short though, I think it could work. -- Stuart Longland (aka Redhatter, VK4MSL) I haven't lost my mind... ...it's backed up on a tape somewhere. ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, Slashdot.org! http://sdm.link/slashdot _______________________________________________ Freetel-codec2 mailing list Freetel-codec2@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/freetel-codec2
