Over the past several months, the EmergencyHam Network has been moving steadily from an idea and an architecture into a working system.
We are now approaching an important milestone. Starting in September, we plan to begin limited alpha trials of EHN with some of our members.
There is still plenty of development ahead, and an alpha trial is exactly that — a chance to put the system into people’s hands, find out what works well, discover what doesn’t, and improve it. But we now have enough of the core system and gateways working that it is time to start testing the EHN concept outside the development environment.
One Identity, Many Ways to Communicate
One of the fundamental ideas behind EHN is that communications today exist in separate islands.
A person might be using MeshCore or Meshtastic when away from cellular coverage. Someone else may only have an ordinary mobile phone. Amateur radio operators have networks such as APRS and HF digital modes, while Internet connectivity opens up still more possibilities, including email and other messaging services.
Each of these systems can be useful, but normally they know very little about each other.
EHN is being built to provide the layer that connects them.
Instead of identifying someone by a particular phone number, radio node or network address, an EHN member has a unique EHN user identity. The EHN directory can associate that identity with the different ways that person can currently be reached.
That means the sender shouldn’t need to ask:
Is Steve on MeshCore, Meshtastic or SMS today?
They simply send the message to Steve’s EHN identity. EHN determines which permitted endpoint and communications path can deliver it.
This is what we mean when we describe EHN as transport independent.
The Base-Station is Becoming Real
A major part of our development work has been the EHN basestation.
The basestation provides the intelligence behind an EHN installation. It handles identity resolution, routing policy, message storage, delivery state and the queues needed when a destination cannot immediately be reached.
Around that core are gateways to individual communications systems.
We now have working integration work for MeshCore, Meshtastic and SMS/RCS, giving us the pieces needed for some interesting first trials.
The gateways deliberately don’t become independent routing systems. They deal with the mechanics of their particular network while the EHN basestation decides where a message is supposed to go.
That distinction will make it much easier to add other communications technologies later.
What might an EHN message look like in practice?
Imagine someone hiking or camping outside cellular coverage but carrying a MeshCore device.
They want to contact a family member who has nothing more exotic than an ordinary mobile phone.
The hiker sends the message to the family member’s EHN user ID. The local EHN basestation receives it through MeshCore, looks up the recipient, discovers an SMS/RCS endpoint and sends the message through the phone gateway.
A reply can make the journey in the opposite direction.
MeshCore ↔ EHN ↔ SMS/RCS
Neither person needs to understand the other’s communications system, and nobody has to manually relay the message.
That’s a relatively simple example, but it demonstrates an important part of what we are trying to accomplish.
What if the other network isn’t available?
Real emergency and off-grid communications aren’t continuously connected.
EHN has therefore been designed around store-and-forward operation rather than treating it as an exceptional condition.
Receiving a message and delivering a message are separate events.
If EHN accepts a valid message but the destination cannot currently be reached, it can store the message and queue it. When a suitable communications path becomes available again, delivery can be retried.
That also means a local EHN station isn’t intended to stop functioning simply because its Internet connection disappears. It retains local identity, endpoint and operational information so that known users can continue communicating using the resources that remain available.
Resilience to broken paths is part of the architecture, not something we intend to bolt on later.
Groups can cross networks too
The same principle becomes particularly interesting with groups.
An EHN group might include people using MeshCore, others using Meshtastic, members who are reachable through SMS/RCS, and eventually participants on other supported networks.
They can still participate in one EHN group conversation.
EHN resolves delivery separately for each participant. A message might therefore leave the same basestation through several different gateways.
Someone temporarily unreachable doesn’t necessarily lose the message either; their copy can remain queued until an appropriate path returns.
EHN isn’t limited to chat
Another area we want to explore is machine and sensor traffic.
EHN’s addressing model includes the concept of a sink — a destination intended to receive information rather than represent another person.
For example, students participating in a distributed environmental monitoring project could have small mesh-connected sensors at their homes.
Their devices could submit readings to an EHN sink. EHN could validate and store those reports and then forward them to a school system, mailbox, web service or other configured destination.
If that destination were temporarily unavailable, the reports could wait in the EHN delivery queue.
It’s a useful example of how the same infrastructure developed for resilient human communications can support other kinds of distributed information.
Amateur Radio Comes Next
For our initial development and alpha testing, MeshCore, Meshtastic and cellular messaging give us an excellent environment in which to prove the core concepts.
But amateur radio remains an important part of where EHN is heading.
We are working toward APRS integration, and HF digital communications are also on the roadmap.
Amateur-radio gateways introduce additional technical and regulatory considerations, so EHN treats them as controlled boundaries. Traffic crossing an amateur RF path must comply with the rules applying to that service rather than simply tunneling arbitrary Internet traffic across amateur radio.
The objective remains interoperability while respecting the requirements of each communications network.
September: time to start trying it
This brings us to the next stage.
During September we hope to begin putting early EHN software into the hands of a limited number of members.
The first alpha trials won’t attempt to demonstrate everything in the long-term EHN vision. We want to start with the fundamentals:
- Can users establish an EHN identity and use it naturally?
- Can messages reliably cross between MeshCore, Meshtastic and SMS/RCS?
- Does store-and-forward behave correctly when we deliberately remove communications paths?
- Can a basestation continue useful local operation when disconnected?
- What happens when real users do things we never anticipated during development?
That last question may be the most important one.
Alpha testing isn’t intended to prove that EHN is finished. It’s where we start finding out what EHN needs to become.
Want to be part of it?
EHN is still a small volunteer project, and September is also when we hope to start expanding the group of people actively involved.
That doesn’t just mean software developers.
We need people interested in testing, radio and mesh networking, Raspberry Pi and hardware, server administration, documentation, emergency communications, training, publicity and outreach.
And we need ordinary users. A communications system tested only by the people who designed it isn’t much of a test.
If you’ve already joined EHN, thank you for your patience while we’ve been building the foundations. We’ll be providing more information about the alpha trials as September progresses.
If you’d like to take a more active role, this is an excellent time to contact us and tell us what interests you and what experience you might be able to bring to the project.
After months spent designing, coding, integrating and testing the pieces, we’re looking forward to the next part: putting EHN in front of real users and seeing what happens.
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