Multi-hop relay
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Multi-hop relay is the technique that lets a message reach a destination beyond direct radio range by passing through intermediate devices. Each intermediate device receives the message and forwards it toward the destination, so a chain of short links adds up to long-distance delivery. It is the mechanism that turns a set of nearby devices into a network that covers far more ground than any single radio can.
How it works
A single radio link reaches only as far as its range. Multi-hop relay overcomes that limit by having devices forward for one another. If A can reach B, B can reach C, and C can reach D, then A can reach D in three hops even though A and D are far apart.
To keep a relayed network stable, each message carries a time-to-live (TTL) that counts down at every hop and stops the message once the limit is reached, preventing endless loops. Messages also carry a unique ID so that relays can drop duplicates they have already forwarded, and receivers acknowledge delivery so senders can retry a lost message rather than assume success.
Choosing which neighbor to forward to is the routing problem. Relays weigh link quality, availability, and load, and the network self-heals by rerouting around a device that leaves.
Why it matters
Multi-hop relay is what makes a mesh cover a venue, a convoy, or a neighborhood without any infrastructure. Coverage becomes the union of every device’s range instead of the range of one radio, and it grows as more devices join.
It also enables reach into places a single link cannot serve: around obstacles, across a large site, or between pockets of devices that could never see each other directly.
How it relates to Offline Protocol
Offline Protocol relays messages up to 8 hops through its transport layer, DORS. Every message carries a unique ID and TTL; receivers acknowledge, senders retry on timeout, and relays deduplicate by ID, so the application sees exactly one delivered or one failed outcome per message.
Relay duty is battery-aware: well-charged devices take on more forwarding and devices low on energy shed it, balancing load across the fleet. Because sessions use MLS (RFC 9420), relay nodes forward only ciphertext. See peer-to-peer mesh networking for how routes are chosen and delivery is confirmed.
Frequently asked questions
What is a hop in a mesh network?
A hop is one link in a relayed path, from one device to the next. A message that passes through two intermediate devices to reach its destination has traveled three hops.
What is the maximum number of hops in Offline Protocol?
DORS relays messages up to 8 hops. The TTL counts down at each hop, and a message that exceeds the limit is dropped rather than relayed further.
Can relay devices read the messages they forward?
No. In Offline Protocol, sessions are encrypted with MLS (RFC 9420), so relay nodes forward ciphertext only. Keys stay on the session members’ devices.
