Monthly Archives: June 2011

APRS: World’s Best Social Mapping and Wide-Area Ad-Hoc Wireless Mesh Network

Technology

That was quite a headline, and I’m going to try to back it up below.

APRS is the Automatic Packet Reporting System. It’s a system for exchanging brief packets of information. It is most frequently used for mapping applications, but it really does a lot more than that. It has its biggest home in the amateur radio world, but isn’t limited to that, either.

The most common way to use APRS is to have some device hooked up to a GPS transmit packets with the GPS information in them. These packets can then be plotted on a map in real-time or with history. That in itself isn’t particularly newsworthy these days.

An interesting thing about APRS is that it’s not just positioning. Let’s say that there was a search-and-rescue operation. A person could draw a rectangle on the map indicating the search area, and within about 3 seconds everyone else’s map also shows that rectangle. People have even been known to play chess by sharing and moving objects on APRS!

The next piece that makes this interesting is that APRS is an ad-hoc mesh network. In its traditional implementation, VHF amateur radio, a radio emits a packet with a geolocation in it (a “beacon”) and any other radio within direct range of that can receive it. Radios can display basic information (such as distance to the other radio, heading, etc.) or hooked up to a laptop or mapping device for a better display. So if everyone is within a few miles, APRS works without any pre-existing infrastructure at all. This makes it wonderful for use in disaster areas, and was put to heavy use in Joplin after the tornado there.

But what about radios that are too far away? Any APRS station could also be a digipeater. When a packet is transmitted, it has a maximum hop count. A digipeater hears the packet, decrements the maximum hop count, and re-transmits it. With this mechanism, packets can travel hundreds of miles. It creates a highly resilient network, one that can route around trouble without even having to have an explicit backup route. I could bring in a digipeater in my car — it can be small enough to hold in my hand — and instantly improve APRS reception in an area.

One interesting aspect is that packets can be digipeated more than the maximum hop count. For instance, if a packet leaves my radio and is picked up by a digipeater to my west and one to my east, it can keep on traveling in both directions. This is part of what leads to resiliency.

APRS also functions over the Internet. There is a large network of interconnected Internet servers that exchange all global APRS traffic amongst themselves. Gateways between the radio (RF) and Internet (APRS-IS) services exist, and are called iGates. They are not generally required, but make useful websites like aprs.fi and email gateways possible. As long as an iGate is within a reasonable number of hops from you, you’re effectively linked. And again, if one iGate drops off, another iGate is probably monitoring your traffic too and you never notice. It’s an ad-hoc mesh network that is actually reliable – how about that?

On the PC side, there are many programs for using APRS. The most common one for Windows is called UI-View, but I don’t use Windows so I can’t comment. On Linux, there are programs (such as aprx) for running your digipeater, but the best-known program is Xastir. Xastir lets you download map files to your local disk, and can interface with the APRS-IS Internet service, radios, weather stations, or simply other arbitrary machines to exchange information. Xastir is a very nice program and is well worth the install, despite its somewhat dated-looking interface.

APRS clients, such as APRSDroid, exist for Android and iOS platforms as well.

So let’s say you’re doing something like helping handle food/water stations for a long bike ride. Even if you don’t have anybody with an amateur radio license, you can use APRS to great effect. At your headquarters, you can run Xastir and turn on its “server mode”. This puts everyone on a map. Then you can have everyone turn on APRS on their phone, and have it report to your custom server instead of APRS-IS. Now you have instant visibility into your entire team’s location and status. If you have transport people driving supplies between locations, that’s especially helpful.

In an amateur radio scenario, you would instead have people with radios at each location, and one laptop hooked up to a radio at HQ. This provides an added bonus of not relying on third-party infrastructure such as cellphone towers.

APRS also has a messaging system, similar in concept to text messaging. It works the same as other things. If I want to send a message to Jane, my radio simply emits a packet that lists the message and Jane as a recipient. It’s digipeated up to its maximum hop count. If Jane is within RF range of one of those digipeaters, she gets the message and her radio ACKs it. Otherwise, it’s delivered into the APRS-IS network — probably several times, which isn’t a problem — and the APRS-IS network delivers it to the iGate closest to her, and from there it gets digipeated the rest of the way to her.

Here’s an example of something created with APRS. While I was on a bus choir tour last weekend, I had a radio with me that was beaconing all the while. Now it was a small handheld radio inside a large metal bus, so it didn’t always have a digipeater in range. But still, you can go see a detailed map with the trail and even see exactly what path each packet took before it hit the Internet.

If you want to try out Xastir, please grab at least version 2.0 – the version in squeeze has some bugs.

Back from Joplin

Uncategorized

I’m just back from spending a few days volunteering with the tornado recovery effort in Joplin, MO.

The biggest image that remains in my mind is of the first time I saw a person picking through a large pile of rubble. The person was standing on top of what used to be a house. Now it was a pile of wood, glass, carpet, siding, and roofing material. I’m sure there was hope for finding some treasure or other — maybe a photo album or videos of children. In any case, it made me feel so lucky, even unfairly lucky, to have not had to go through that.

This scene was repeated several times, but mostly the houses that devastated appeared abandoned by the time we were there, now two weeks after the event.

But I heard stories, and lots of them. The victims of the storm, who were perhaps trying to rebuild that part of their house that got smashed by a tree or a pickup, or trying to get their intact belongings out before abandoning the house, or whatever, were mostly surprisingly upbeat. They were working out in 95-degree heat, many without electricity, running water, or sewer service. Almost every person I met that suffered a loss from the tornado wanted to tell their story. Many also told of their plans for the future, which were full of hope and even upbeat. These were people doing a hard job in terrible conditions and still showing hope.

Another testament to the disaster was the most unusual set of vehicles you’ve ever seen parked at any hotel you can care to think of, for at least an hour-and-a-half radius in the direction I came from. Besides the usual cars and minivans, there might be FEMA vehicles, electric company trucks, Red Cross vans, construction trucks of every kind, police and law enforcement from all over, etc. There was quite obviously an influx of people helping out in Joplin.

My primary task there was to provide communications support for the effort as an amateur radio operator. Amateurs (or “hams”) are something of a volunteer first responder of sorts during times of crisis; most of us own and are very familiar with operating equipment that can communicate over very long distances without the need for any on-site infrastructure. Amateur radio was the only method of communication for some Joplin hospitals in the immediate aftermath.

The communications emergency is over, but the response isn’t. I was assigned to work with the Salvation Army. They were doing a lot of things in Joplin, and had hundreds of volunteers working with them. I don’t think I even know what many of them were doing – I do know they had set up several warehouses across the city working with donating clothing, food, etc.

The part I was involved with was primarily the canteen operation. The SA sent in food service trucks from several parts of the country. These trucks would roam up and down the streets in the damaged area, trying to get past every single street several times a day. Anybody that we could see would be offered food and water. No strings attached, no questions asked. This included homeowners, electric line workers, construction crews, sanitation workers, and quite a few nonprofit groups that sent well-meaning and useful volunteers into the area but didn’t think to provide them with a large supply of water due to sending them into an area without any. Oops. In any case, with extreme heat and no running water, conditions were dangerous. The canteens also knew of certain at-risk families that were living in homes that were mostly intact in the disaster areas, and made a special point to check in on them. They also generally looked to make sure that people looked like they were healthy. Each canteen also had a counselor on board that would visit with people while we quickly prepared their meal — they all seemed to welcome that.

Amateur Radio’s Role

The operation of this size had quite a logistics challenge. I’d hear of things like an unexpected need of 70 lunches, or a semi showing up with donations before there was space, or an unexpected but very welcome donation of a large quantity of ice cream without a place to store it (so the canteen trucks, which have freezers, needed to pick it up quickly). That’s where us hams came in. Each canteen had an amateur radio operator on board. Each major location also had a ham stationed there, and the head of operations also often had a “shadow” — a ham that would follow him around wherever he went to relay messages back and forth. We also had hams with pickups (with radios in them, of course) that could transport things around the city to places that needed them, hams at headquarters managing all the communication and generally investigating questions that didn’t have immediately obvious answers, etc.

Radios were used instead of cellphones for a few reasons. One big one is that everybody on the operation can hear what everyone else’s needs are, since it’s a group communications situation rather than one-to-one. It’s easy to give a general alert to everyone (“come get your ice cream now please!”) and people that have suggestions can chime in. This came in extremely handy more than once. Also, it frees the people doing other jobs from having to spend time chasing someone’s voicemail, finding phone numbers, etc; that gets delegated to us in some cases. I heard from the head of canteen operations, for whom this was the first disaster he’d worked that had amateur radio support, how wonderful it was to have this going on. I also heard a secondhand report that some police officers that were also amateurs had listened to our operation and reported that “we sound more professional than 911 dispatch and do a better job.”

On Sunday I was assigned to a canteen. This meant I didn’t have a lot of radio traffic to pass, so although I had it in my ear all day, I wasn’t actively talking on the radio very much. So I rode in back, helping hand out water, carry meals to people, and so forth.

On Saturday, I was the shadow for the head of operations. That was a difficult task, because he barely ever moved at a pace slower than a run, sometimes would abruptly zip out somewhere, etc. But it was also enlightening and vital. He was a real “get it done” sort of guy, and was the key to quite a few things. Having someone available to relay questions to and from him was a good thing.

And today I worked as a transport person and at headquarters. Due to not having a pickup there, I didn’t actually get called on much to transport things, but in general between jobs the whole time I’d act as a runner if needed, or simply try to figure out the details of how things were run for next time. I wound up taking “net control” (being the control operator at headquarters, and generally managing communications so that people don’t talk over each other and such) for about an hour. So I got to do a little of just about every amateur radio task.

Thoughts

I am thankful for the opportunity to go, and the good feeling of helping people in need — the first I’ve ever had the chance to do that in a disaster. It’s a good feeling to have a skill that is useful and appreciated. Sometimes it felt like handing out food and water is something pretty small in the scheme of things. But on the other hand, it gives people a chance to have contact with someone that cares, an opportunity to have people that can notice problems drive by a few times a day, and an opportunity to help meet people’s basic needs. And sometimes in a fluid situation, there might be more volunteers than are needed, so I did spend some time sitting waiting for the next task.

But overall, I’m convinced that the work I helped facilitate was a good thing and provided a good and needed service in Joplin. This has been quite the experience and I’m sure it’s changed me too, though I don’t yet know how.