Questions

What is UMSH?

UMSH is a mesh networking protocol that enables long-range, low-power, secure text messaging, without relying on cellular infrastructure or internet access.

UMSH devices contain LoRa radios and run firmware that implements the UMSH protocol.

The UMSH app allows you to use a UMSH device from your phone to send and receive text messages, much how you would using any other messaging app; the difference being that the messages are not sent across the internet but are instead routed over the UMSH mesh network.

Why another protocol when Meshtastic and MeshCore already exist?

UMSH started as an exploration of how to improve on MeshCore’s security and protocol design. It borrows many good ideas from MeshCore, including public-key identities, source routing, and regions. But some improvements require changing the packet format and cryptography, which would break compatibility with existing devices.

Starting fresh makes it possible to design those pieces together: authenticated encryption, replay protection without depending on clocks, optional forward secrecy, and private messages that can also conceal who is talking to whom. UMSH also separates message content from packet forwarding, so new applications can use the network without every repeater needing to understand them.

That freedom is the reason for another protocol. UMSH can experiment with changes that are difficult to make in an established network, and the ideas are free for other projects to adopt. The tradeoff is maturity: UMSH is still a technology preview, and Meshtastic and MeshCore have substantially more deployment experience behind them.

Is it ready to use?

It is ready to use, test, and experiment with—but not yet to deploy extensively. It’s a technology preview. Nodes talk to each other, messages arrive, encryption happens, and the app works, but the protocol is still moving and will keep moving. Expect changes that break compatibility and expect to reflash your radios when that happens.

There’s no installed base to protect yet, so when a design decision and backward compatibility are in conflict, the design wins.

If you need to deploy something today that is more mature, you should consider Meshtastic or MeshCore.

Can UMSH talk to Meshtastic or MeshCore?

Not today. The packet formats, the cryptography, and the identity models are different at the lowest level, so this isn’t a setting somewhere—a radio runs one of these protocols at a time, and anything joining the two would have to be a node that speaks both and translates.

The radios themselves aren’t locked to anything. UMSH runs on the same boards those projects run on, and you can flash back and forth as often as you like.

There is some possibility that MeshCore support may be added to the app and to repeaters so that repeaters can forward both MeshCore and UMSH traffic, and the app can communicate with contacts from either. But that’s far from decided.

What hardware do I need?

At least two radios (or a radio for yourself and someone else with a radio), since a mesh with one node in it is just a radio. The hardware page lists everything supported.

Does it need internet access or a cell signal?

No, but you do need some hardware in addition to your phone.

Can I use it on amateur radio bands?

Yes, it was designed for that. Authentication is separable from encryption; it’s only the encryption that the amateur radio rules explicitly prohibit. UMSH can work in an authentication-only mode.

Additionally, operator and station callsigns have their own compact encoding, and repeaters update the station callsign as they pass a packet along.

Note, this mode isn’t yet exposed in the iOS app but it will be soon.

Is there an Android app?

Not yet, but hopefully there will be at some point.

How much of this was written by an LLM?

Quite a bit of it. The protocol specification benefited from LLMs to improve readability and for helping to research the comparison chapters.

The reference implementation, the dissector, and the app were largely written by LLMs (under heavy human supervision).

There’s a longer note about it in the repository, including why I don’t consider UMSH slop.

What’s the license?

The code is dual licensed under Apache 2.0 and MIT, at your option.