Order-independent reassembly
Fragments may arrive by any path in any order.
Technology · Transport · Whitepaper
240 bytes. Acknowledged per hop.
The mesh transport carries sync digests, positions, canned messages and the second link of the emergency chain over LoRa. This page documents the framing, the key schedule, the repair behavior and the limits — including the ones that make it unsuitable for some traffic.
01 / Problem statement
What this has to solve.
LoRa gives extraordinary range for milliwatts and almost no bandwidth. A protocol built on it has to accept three hard limits.
The frame is tiny. A useful payload is around 240 bytes. Anything larger is fragmentation, and fragmentation over a lossy multi-hop link is where naive implementations fail.
Duty cycle is regulated. ISM band duty-cycle limits cap how much any node may transmit. A protocol that ignores this is either illegal or unreliable, depending on jurisdiction.
Topology is unstable. Nodes move, terrain occludes, batteries die. A route computed once is wrong within minutes.
02 / Mechanism
The design, component by component.
- Framing
- Payloads are fragmented into 240-byte frames carrying a message identifier, fragment index, total count and a per-fragment integrity check. Reassembly is order-independent; only completeness matters.
- Key schedule
- A per-message key is derived from a rotating chain. Forward secrecy means a captured node yields its forward traffic, not the network history. Rekeying is implicit in the message, not a separate exchange.
- Acknowledgment
- Per hop rather than end to end, so loss is attributed to the link that lost it. A retry goes out on a different path rather than repeating the same failure.
- Liveness
- Beacons are jittered. A missed beacon window marks a peer down; path recomputation and the first retry complete inside two seconds.
- Duty-cycle governance
- The stack accounts for its own airtime and defers non-urgent traffic to stay inside regional limits. Emergency traffic pre-empts.
- Priority classes
- Emergency, position, sync digest and bulk, in that order. A sync digest never delays an SOS flood.
- Store and forward
- Unattended relay caches accept traffic for a bounded window and advertise what they hold with its age, so undelivered traffic is visible rather than assumed.
03 / Properties
What this guarantees.
Forward secrecy
Per-message keys from a rotating chain.
Localized loss attribution
Per-hop acknowledgment.
Sub-two-second repair
Beacon gap to first retry on a new path.
Regulatory duty-cycle compliance
Self-accounted airtime with emergency pre-emption.
Four priority classes
Emergency traffic is never queued behind bulk.
Bounded store and forward
Held traffic advertised with its age.
04 / Reference
| Parameter | Value | Note |
|---|---|---|
| Bands | 868 / 915 MHz ISM | Region-dependent |
| Frame payload | 240 bytes | Fragmented above this |
| Reassembly | Order-independent | Completeness only |
| Key rotation | Per message | Derived from a rotating chain |
| Acknowledgment | Per hop | Not end to end |
| Repair target | < 2 s | Beacon gap to retry |
| Priority classes | 4 | Emergency, position, digest, bulk |
| Duty cycle | Self-accounted | Emergency pre-empts |
| Not suitable for | Video, bulk imagery | Use satellite or cellular |
05 / Process
Traced, node by node.
Small frames. Strong guarantees.
Read the sync fabric next for what actually travels over this transport.