Hi all, Is someone able to point me to some documentation on how NET/ROM Level 3 operates? Basically I'm working on a small project¹ to see if I can get IPv6 flowing over AX.25, taking ideas from 6LoWPAN (e.g. RFC-4944).
The aim here will be to enable 6LoWPAN mesh networks to inter-operate with a AX.25 backbone network and to enable easier construction of software that utilises the AX.25 network. The thinking here is that 6LoWPAN operates under similar constraints to AX.25 (slow radios, uni-directional communications, changing propagation patterns, small payload size, etc) and thus could be adapted to work over AX.25. One thing that IEEE 802.15.4 appears to provide which is absent in AX.25, is automatic L2 routing. If you happen to know how to know the intermediate digipeaters between stations X and Y, sure, AX.25 will deliver them there, but you have to figure this out first. It would appear that Net/ROM solves this problem already. In particular, from what I've read, it's in two parts, Net/ROM Level 3 forms the graph, while Net/ROM Level 4 switches virtual "circuits". Using one of these circuits would be a silly idea for IP traffic for the same reason that TCP/IP over TCP is usually not advised (ARQ messes up TCP/IP). It's also point-to-point, which defeats the purpose of using IP (might as well throw raw TCP and UDP messages down the wire). However, if I could participate as a Net/ROM node, I can use that to build up my graph of connections, then send UI frames with a different PID that encodes the IP datagram, and send it via regular AX.25 through up to 7 digipeaters. Further distances can be achieved via L3 routing within IPv6 (e.g. using geographical methods² to derive a subnet, this could be refined a bit). As for application services, anything that can work over 6LoWPAN could potentially work for this too. I'm thinking along the lines of CoAP, maybe MQTT, NTP, TFTP, etc. Anything which has a nice small payload size, and ideally UDP-based. Multicast routing could be used for "group" applications (e.g. emcomm co-ordination, chat groups, etc). The challenge has been digging up how Net/ROM operates. Google happily points me to a company named NetROM, or to the AX.25 spec from the TAPR, or to various pieces of software that use Net/ROM (such as ax25-tools), but apart from digging into the kernel sources, I haven't seen much that would describe how this is actually operating. Is someone able to shed a light on how this lower half of Net/ROM actually operates? -- Stuart Longland (aka Redhatter, VK4MSL) I haven't lost my mind... ...it's backed up on a tape somewhere. 1. https://hackaday.io/project/161975-6lowham 2. https://stuartl.longlandclan.id.au/blog/2011/02/05/geographic-ipv6-using-maidenhead-locators/
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