WiFi Based Push-To-Talk And Mesh Networks

A couple of years ago I did a posting on Mesh Networks. It was in the context of government shutdowns of networks during protests. It is just as applicable during times of natural disasters.

At present, in Puerto Rico, one of the biggest problems is that most of the communications networks are down. Cellular Telephones are slowly coming back up, but they will be clogged for quite a while even once up.

For this reason, it is worth looking at that prior posting. So folks can be reminded how to set up a mesh network for local dedicated communications (and some folks can set up things like HAM radio data bridge connections to get simple text email in and out).


Seeing as that is a rapidly moving field, and that it’s been a couple of years, there are likely some new players and new products out there. I’m not intending to search that space again in this posting, but if anyone knows of a newer cooler application, let us all know.

What has happened that I find particularly interesting is that folks have started to find ways to use regular WiFi networks for group communications. Even if the connection to the Internet is down, various local WiFi hotspots can be used for very local communications, and extended Mesh Networks of them can spread over a significant area.

For example, I can have a WiFi hotspot running in my home, and set up a Raspberry Pi as a router to a neighbors WiFi. Jointing those two into one network would mean anyone connected to either of us could have a ‘radio’ to anyone else connected to us. That kind of Mesh Network could rapidly be spread over a neighborhood. Then, if even ONE person has a connection to another nearby similar local area network (say, via a hacker with a CanTenna for a couple of mile range) those two neighborhoods can be joined.

That’s the network layer, which is all well and good, and for us Linux folks more than enough to set up file transfers, UUCP based email, SMTP based email, VOIP, etc. etc. But for most folks with a phone or a tablet, they don’t have the “Applications Layer” needed to run over the top of it. That’s what this posting is mostly about.

So, for example, say you were a Major Network Reporter on the scene of a significant disaster. You have a nice broadcast truck, with satellite uplink for your video, and maybe even SatPhone connections. Possibly also a data plan for sending data over those same links. IF you set up a local WiFi Hotspot in your truck, all your crew, and any local folks you let on (say First Responders) would have a PTT (Push To Talk) Radio ability between them all. Bridge that via your data link to the mainland, you now have PTT radio to anyone else with the application. You become a center of communications between the Disaster and the ROW (Rest Of World). A Packet Radio Bridge of a sort.

People (and their stories) will come to you, from miles around. As a communications hub, you also become the hub of stories, and don’t need to go hunt them out. They come to you.

So what IS this Magic Sauce that lets my cell phone or tablet become a PTT radio over WiFi? There are several players and choices. The one that I heard about (on some obscure news source) was being used by some small groups in some disasters already. It is Zello.


Now, some of you will already be realizing the flies in this ointment… First off, you need some minimal electric power to run your WiFi Access Point / Router (and you need to have a WiFi Access Point Router other than the one from the Telco if that one has you locked out of configuring it…). That’s about $75 up front cost and a Preparedness Mindset to have bought it before Shit Happened. In a real Disaster, you could likely scrounge some of it from destroyed stores; but be aware that casts you in the role of “Looter” rather than “Hero”. At a minimum, leave an I.O.U. and your contact information showing honest intent…


You may have the opportunity for higher levels of power preparedness:


As per access points, there’s a zillion of them:


Lots of folks, like me, have a private WiFi access point router in their home and let it connect to the WiFi Access Point router installed by the Telco. This adds a layer of protection, some complications, and it means your local WiFi stays up even if the Telco Router gets zapped. I have a couple of old ones in boxes, too. Deprecated and slow, but workable. Or, the local tech guys can just build one. ( I once turned a Windows computer into a 5 port Ethernet router and WiFi Hotspot…). I’ve made my Raspberry Pi into an access point from time to time. Once, when AT&T had the DSL die, to retain internet access via a T-Mobile HotSpot device. Had the whole house running through the Pi to the T-Mobile to the world… So this isn’t a hypothetical…


For some folks, their phone allows them to “tether” their computer. Make that computer a router / hotspot and you have internet for the space near you, and that means PTT Radio too. (Limited by the bandwidth available in a real disaster as folks fight for cell phone space…)

So, once you have some kind of power, a WiFi access point set up, and / or meshed, and / or built from whatever computer things are laying around, how does that WiFi Radio thing work and what’s this Zello thing? From their site (link above):

Walkie Talkie App

Push the button for instant, radio-style talk on any Wi-Fi or data plan
Free download

Now there’s your first “wake up call”. It’s a “free download” (for up to 5). But that means you can’t get it until you have internet access which you don’t have… So download it before the disaster, OK? (or one of the alternatives). During a disaster, folks on systems that leave you in control can just copy the app from one to another. Folks with a “lock-in” to an “app store” need to either know how to “Jail Break” their Android or iPhone, or they are basically stuck. Hopefully there is some other way to get apps for them. Once a local site with internet access is set up, you can start a download process, but frankly, 100 kB of “Mom, I’m safe!” for 5000 people are going to be more valuable than a 100 kB download for one, IMHO. So best if set up ahead of time or if a high speed download spot were set up in a disaster area. Once you’ve got it, it ought to work on an isolated network. (I’ve not tested that, so I’m hoping they don’t have any kind of “phone home” obligatory check-in to work…requiring ongoing internet connectivity.)


Fast, secure and reliable push-to-talk

Works with smartphones, tablets and most rugged mobile computers
Manage users, channels, and settings with a browser
Advanced encryption ensures all communications are secure
Connects to existing LMR radio systems
Free for 5 users, with no time limit

At the bottom of that page they say they have a new “home” for Zellowwork. It is unclear to me if this replaces zellow.com or is just a ‘work’ oriented extension / specialization, but that’s for others to work out.


Unlike two-way radios, Zello works with any data or Wi-Fi network.
Private Communications

All team conversations take place on your own private Zello network.
Simple pricing

Free trial for 5 users. No credit card required.

$6 per user per month No contract, cancel at any time.

Supported Platforms
Everyone’s covered.

Windows Phone
iPhone, iPad, iPod Touch
Windows CE, Windows Mobile
BlackBerry, BB10
Windows PC desktop
LMR / Two-way radio gateway

So, basically, if your local emergency radio towers are down, your Telco is flooded, your Cable WiFi is out, and you have a group that needs to coordinate between those digging rubble, those preparing water and aid stations, and those with dogs or medics, pop up a WiFi Hotspot from your truck battery, and start talking. IF you have prepared for it with material and software download…

(It would be Very Good Advertising were Zello to fly in a few clusters of this already set up… Hint. Hint. And maybe a local download box…)

Are there other choices? Yes. Some, like the Raspberry Pi, need more hands on than others. The Pi doesn’t normally come with microphone and speakers, so you must do the hardware work to build it in advance… Not very useful in the middle of a disaster to be ordering up microphones and speakers and cases to be delivered “someday”… but good to know about in advance.


On a cursory examination, this one looks similar. I’ve done no examination of the particulars, and have no idea if there is any “free trial” option.


There are likely other free apps that do something similar on the various “Apps Stores”. This one, for example:


I don’t know anything about it other than DuckDuck go found it and what the App Store says about it:

With Wi-Fi Talkie you can organize communication between devices at distances of Wi-Fi signal without using an Internet connection or a cellular network.

• Working without Internet or a cellular network
• Voice calls
• Transferring files and folders at Wi-Fi speed
• Group chat
• Private messages

1. Connect an existing Wi-Fi Network or create your own wireless network based on a Hotspot* of your phone or tablet, using “Network Manger” of Wi-Fi Talkie.
2. Say people around you to connect the network you are connected.
3. Now you can use full functionality of Wi-Fi Talkie!

• Good sound quality even if a Wi-Fi signal is very weak
• Unlimited number of active calls
• Speakerphone mode
• Bluetooth headset support
• Wired headset support
• Noise reduction

The range of Wi-Fi signal depends on a hotspot and connected devices. Usually the range is not more than 50 meters (150 feet) indoors and up to 150 meters (450 feet) outdoors.

• Now you can communicate with people in previously unavailable places: airplane, train or any other long-distance transport, forest and mountains, stadium, concert hall and other public places where a cellular signal is weak.
• Wi-Fi Talkie is also well suited for communication within a Wi-Fi network of your home, office, school, university or dorms.

(*) If you create a hotspot while your device’s Internet connection enabled, then Internet tethering (sharing) becomes activated.

Wi-Fi Talkie Localized to:
English, Spanish (Español), Arabic (العربية), Portuguese (Português), German (Deutsch), Indonesian (Indonesia), Russian (Русский), Bengali (বাংলা), Burmese (ျမန္မာ), Turkish (Türk), Serbian (Српски).

I’m sure there are more for the various platforms.

The point here is not to finger one particular solution, but to get the point across that:

When all the Telcos and Towers are down and out, YOU can be your own WiFi Telco with just a few Watts of power, a WiFi HotSpot, and an application. Interconnect or Mesh those, and you can cover a small town or region.

For those with a hardware bent, you can make “intercom” or “WiFi Radios” out of the Pi, with time, talent, and advance planning:


My wife and I often find ourselves trying to communicate while working in two different offices in the same house. Seems like a simple problem, but some messages are not worth the extra hassle to email, send an instant message or the dash down the hall. Normally, it ends up with someone just screaming to the next office.

When the second RaspberryPi arrived (Farnell delivered it in two days), I decided to try a simple push to talk solution called Mumble. Mumble is used in the gaming world and is similar to other VoIP chat solutions like Vent and TeamSpeak. You can can define the keys you want to trigger ‘push to talk’ or you can type a message similar to instant messenger.

You can also mute yourself or deafen yourself to avoid unwanted messages while on a call. The other party can see your status.

Mumble clients are available for Mac, PC, and iOS. We have tested them all out over the last week and have had no issues with ~5 devices connecting to the Mumble server, called Murmur, running on the Raspberry Pi.

Getting Murmur started was easy. I followed the these directions and had no problem getting it up and running on the Pi Wheezy distro.

One Note – if you are using Mac/iOS make sure you have Avahi Installed.

Note that they used the Pi as the Server, and other computers as the end devices where a microphone and speakers are needed.

These folks add the hardware to the Pi:


In Conclusion

My point here is pretty simple. As I’ve said many times: If you allow ANY communications, you allow ALL communications. All that changes is the data rate and the creativity required. These are examples of how folks can set up their own local communications and even bridge them out to the greater world, by NOT waiting for Central Authority, Telcos, etc. etc.

Yes you CAN set up your own local area network, yes you CAN set up your own local WiFi network hotspot, yes you CAN interconnect or mesh with others, and yes you CAN make many common devices into PPT Radios for local (and not so local…) communications.

Pre-planning helps, but even in a disaster some of this can be done after the fact. Folks flying in to help in the recovery can download apps now and put a WiFi hotspot and small inverter in their pack and be “ready to go” on the ground, even if regular comms are missing.

The important point is just that it is within the budget and abilities of most folks to “Make It Happen.”

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About E.M.Smith

A technical managerial sort interested in things from Stonehenge to computer science. My present "hot buttons' are the mythology of Climate Change and ancient metrology; but things change...
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2 Responses to WiFi Based Push-To-Talk And Mesh Networks

  1. E.M.Smith says:

    This article is about folks doing just this in a neighborhood. How to build a local mesh network when you aren’t getting the service you need:


    How To Build A Low-Cost “Wi-Fi Mesh Network” For Emergency Communication
    A community in Brooklyn is pioneering a simple, low-cost solution to the “last mile” connectivity gaps that telcos can’t (or won’t) bridge.

    By David Lumb

    When tropical storms hit New York City, internet connectivity is often the first thing to go down. The next time it happens in the low-lying coastal community of Red Hook, Brooklyn, it will be a group of teenagers running something called a Wi-Fi Mesh Network that will come to the rescue–providing a model for a low-cost, community-built solution to the so-called Last Mile gaps that the massive telcos can’t (or won’t) bridge.

    A year ago, a community organization called Red Hook Initiative (RHI) had just started a pilot program for a Red Hook Wi-Fi mesh. A “mesh network” is a system of inexpensive router nodes that beam Wi-Fi around above the streets for everyone to use, and even if the internet connection goes down, the mesh allows communication within its bounds. So while you can’t watch Netflix over a closed mesh network, you can still communicate with people in your vicinity–which is obviously crucial in emergency scenarios.

    In the hurricane’s aftermath, RHI handed the reins of the Red Hook Wi-Fi mesh project to a new group calling themselves The Digital Stewards, comprised of eight 19- to 25-year-olds. Do we really want kids running our backup systems?

    As it turns out, RHI has lots of experience getting middle school and high school kids in its youth programs to stay on for leadership positions, but the Digital Stewards is a one-of-a-kind job training experience. Over its year-long course, not only will the youth have built up technical skill installing and maintaining their Wi-Fi network–they’ll have built lasting infrastructure in their own community, where their own neighbors are relying on their technical expertise.

    But getting this mesh network started relied on an entirely different network–specifically, RHI Director of Media Programs Anthony Schloss’ network of tech professionals. His contact with the New America Foundation’s Open Technology Institute (OTI) led to a partnership to adopt its open-source Digital Stewards curriculum, already piloted in a team in Detroit, for Red Hook’s youth. In exchange for code line-level tech support, financial assistance, and personnel visits to share expertise, the Washington, D.C.-based OTI uses the Digital Stewards as a guinea pig for their vision of wireless community connection: Commotion Wireless.

    Citing the state-led disabling of local Internet during the 2011 Tunisian and Egyptian protests, OTI presents Commotion’s open source wireless receivers/transmitters as a lynchpin of both everyday local interaction and as a civic network secure from government interference.
    While protecting against state censorship/intrusion isn’t anywhere on Schloss’ priority list, privacy concerns have driven recent interest in Wi-Fi mesh since the Snowden NSA leaks. Regardless of motivation, the low expense of Wi-Fi mesh allows the scrappy network concept to be set up anywhere, as Schloss learned when his nascent network got FEMA’s attention in the days after Sandy and they hooked it up to their satellite connection, spreading wireless internet around Coffey Park where the Red Cross had set up shop.

    It then goes into more depth about just how you do it.

    How To Build A Wi-Fi Mesh

    Currently, Schloss and the RHI pay local ISP Brooklyn Fiber to stream internet through a five-router distribution layer of Ubiquiti Nanostation routers (which have about a mile line-of-site range) mounted on tall buildings, which in turn relay the signal through omnidirectional Ubiquiti Pico omnidirectional Wi-Fi routers–which are tough, waterproof, cheap ($80), and low-power (about $20/year each). Those area routers project Wi-Fi as normal at speeds of 6-10 MBps–quite enough for mobile Red Hook users, but not enough for sustained desktop data download (which nobody has abused to torrent massive files yet, says Schloss). The Digital Steward youth install the Pico routers themselves in less than an hour, either attaching router nodes to windows via adhesive or installing roof mounts, which often requires drilling.

    It is important to note that you do not need those particular bits of kit. Any WiFi Router that lets you configure routing can be used. Range and specific configurations will vary, but it will work. Even a Raspberry Pi with a WiFi antenna is fine. Higher end higher power routers with miles of range often require licenses, so unless you are willing to “go there” you are instead in the low power unlicensed group (with optional directional “cantennas” for longer range links.

  2. E.M.Smith says:

    I thought I saw one of these at the Drag Races. Looks like it is real. Cell Tower on a ruck:


    Mobile / Portable Communication Towers
    Integrated Tower Systems is recognized as the world’s premier OEM-source for rapid-deployment of Mobile Communication Towers, Portable Tower Systems, Communication-Sites-on-Wheels/Light-Trucks (“COWS” and “COLTS”), and Mast-, Satellite- and Tower-Integrated Mobile Command and Communication Centers. An innovative and extensive line of Commercial-Off-the-Shelf (COTS), customized and Military-Spec portable tower solutions support the emergency response, temporary and long-term communications, surveillance, test and other common and proprietary requirements of a global clientele. When situations require higher payload elevation and/or heavier payload capacity, Integrated Tower Systems self-supporting telescopic lattice tower structures deliver the ultimate in performance. ITS towers can elevate payloads from 38 feet (11.5 m) to 106 feet (32 m) standard, and customized to 130 feet (39.5 m)

    I think the emergency response for Puerto Rico needs a load of these flown in…

    Looks to be many sources too:


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