Under the Hood: How to Engineer Next Gen. WiFi Calling

We care about call quality

When you’re using your Republic phone to keep in touch with your friend, your calling experience is measured by the content of the conversation, not the quality of the call. However, when your network zigs instead of zags and you lose some audio, your focus is shattered. The conversation suffers. This is a worst case scenario for a Republic Engineer. We’re continuously looking for solutions to minimize the probability of an audio drop, and now we’ve rolled out something we’re very excited about – Bonded Calling™.

Bonded Calling™ is one factor in the Republic Adaptive Coverage™ offering. Adaptive Coverage™ itself describes the entire history of Republic Wireless WiFi calling: seamless handover from WiFi to Cell and back again, and advanced algorithms for determining the optimal time to handover your call. But there’s a new tech in town! We’ve named it Bonded Calling™, and in short, it uses the cell data connection of your phone to supplement a WiFi call during a rough patch. As we dive into how this works, we’ll follow the journey of your voice, as it is digitized and slung across the world.

Your voice disassembled

Your phone initially receives your voice as an analog signal. Through various hardware and software elements, the signal is transformed into a digital stream of bytes.

When we talk about a stream, or frankly anything digital, it’s important to keep in mind that things that appear continuous in observation are in fact made up of tiny discrete pieces.

For example, your laptop display is shining millions of tiny dots into your eye, which your brain interprets as a single image. Likewise, it’s not possible for us to transmit a truly continuous signal over the Internet, so the stream is packetized; we split the stream into segments that are each 20 milliseconds in duration (that’s 1/50th of a second, roughly comparable to the duration of a single video frame).

Your phone breaks up your voice’s audio signal into short pieces.
Your phone breaks up your voice’s audio signal into short pieces.

These audio packets must arrive on the Internet backbone, the critical network of physically connected computers that make it possible for you to stay connected to the rest of the world. But how do we get them there? The obvious choice is to send them via your home WiFi network; on average it’s your most reliable and fastest connection to the Internet. This is how all WiFi calls start, but your phone is mobile, and so are you. For example, maybe you go out to the mailbox while you’re on the call. Your WiFi network may struggle to keep up with the increased range. Republic can detect the change in WiFi and hand the call over. But with Bonded Calling™, the story is a bit different.

Cell! WiFi! on your marks

Your phone detects that your audio packets are missing, are out of order, or are coming in later than expected, and acts quickly! It establishes a mobile data link over the underlying cellular IP data network. We duplicate each audio packet and send one over each available transport — one over WiFi and one over Cell.

Call Bonding begins by duplicating each audio packet and setting different transports for each.
Call Bonding begins by duplicating each audio packet and setting different transports for each.

The Republic server listens for both, and takes whichever wins the race. Fifty times per second we are conducting a race between Cell and WiFi and awarding the winner a spot on the final audio stream playback.

Fifty times per second we are conducting a race between Cell and WiFi and awarding the winner a spot on the final audio stream playback.

(above the line) The packets in flight have varying delivery times. (below the line) Republic takes the first packet to arrive and constructs the audio stream.
(above the line) The packets in flight have varying delivery times. (below the line) Republic takes the first packet to arrive and constructs the audio stream.

The resulting audio output is the amalgamation of packets received over WiFi and Cell, a tapestry stitched together with threads 1/50th of a second in width.

The result is a crisp and smooth audio stream for playback on the other end. Your conversation doesn’t miss a beat.

In this example, Bonded Calling™ has protected your voice from being garbled, and it’s not only one way. This entire process works in both directions at this breakneck speed, with your phone and the Republic server working in tandem to make smart use of supplemental data over the cell network. Your voice is protected, and your friend’s voice is protected.

We are always trying to stay conscious about smart use of WiFi and Cell networks. So your phone and the Republic servers are constantly measuring many aspects of your calling experience and toggling Bonded Calling™ only at the appropriate times. And keep in mind that the cell data used here is never attributed to your monthly usage.

When the race is just too slow

Sounds great so far. We’ve all hit WiFi rough patches, but we’ve all hit those cell data data spots as well. In the packet race, If WiFi and cell are both getting frequent DNFs, then we have some additional work to do.

When Bonded Calling™ is engaged, we’re continuously measuring the performance of the cell data network. In the rare case that both the WiFi and Cell data network are together unable to maintain a high quality audio stream, we still have our tried-and-true handover in our back pocket. Your call transitions to the circuit-switched cell network, and your conversation continues without a hitch.

Here’s what really matters

Even as an Engineer, I still think the Internet is full of magic. No one person can understand the full stack of technology that keeps us all connected. No one person should have to. We’ve scratched the surface of the Bonded Calling™ implementation, but it’s all for one thing: if you’re on a call and you can’t tell any magic is happening, then we’ve done well! This is the standard that we measure ourselves by, and it won’t stop with Bonded Calling™. The search for quality is continuous and never-ending. With this search, we are striving to empower your real experience — keeping in touch with those most important to you.

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  • c3tobor

    Thanks for the well crafted and simplified description of the Bonded Calling technology.

    DNF= ‘Did Not Finish’?. 🙂

    • bitflung

      DNF: i was wondering the same. i figure it has to do with fragmentation. maybe “do not fragment” (usually abbreviated to DF)?

      • Jesse S

        Apologies for not defining my terms! It does in fact stand for “Did Not Finish” as a riff off of the WiFi vs Cell racing analogy.

  • rcxb

    Just tell me we can shut off this option, easily… The last thing I want is to do is run-down my phone battery twice as fast. Plus switching back and forth between low-latency WiFi and high latency cell data sounds like a recipe for a worse, not better, call experience. And this all for what benefit? Switching over to cellular voice call when the WiFi signal gets bad, seems just fine to me…

    Maybe I’m just gun-shy with lowsy VoIP-over-cellular-data call quality on FreedomPop, as well as the extra 1sec of voice latency RepublicWireless hybrid calling already introduces, and desperately wish not to find the situation get ANY worse than it currently is!

    • https://disqus.com/by/sandratrusso/ DasFluchen

      Turn off your WiFi. There problem solved.

      Its best if you never turn your phone on for maximum battery life. Unless you’re on a active call 24/7 I don’t think you’re going to notice a difference in battery life.

      • Post Fab

        Der große weise Fluch Macher~~~

        Blips in cell-to-“wiffy” (as the Brits say) hand-off–and vice versa–improved radically since the 1st Republic launch (and I quit Republic the 1st time). MOST of the time, call quality is quite acceptable. Cellular data service, OTH, is a shameful shadow of “Real” carriers like ATT & Co.

        However! For any and all data/Internet/streaming media/directions and the rest of the zillion things besides verbal chat for which we our lives depend on our phones, the mobile wiffy–o.k. “wifi” if you insist–is a TOTAL NON-STARTER.

        Urban areas are impossible because whether afoot or horseback, one is constantly swimming through literally DOZENS of wifi zones, many of which are fully or partially unlocked. The produces a crazy-making judder in the signal a Republic phone is processing, with highly erratic buffering and latency along with typically dropping out just as one’s GPS app is delivering THE critical direction for the turn to reach one’s destination or some other desperately needed datum relative only once for that particular place and time.

        Republic voice service alone is good enough for this price point, Ditto data when on one’s own wifi network. But once you step outside your own space, you are hopelessly mired in the ridiculously crappy data service.

        Bottom line: Republic is a good choice for cheap cellular voice service, but for people who don’t need (or perhaps do not even understand the importance of) rock-solid dependable Internet access 24/7.

        Further . . . “Bonded Calling™ “is sophomoric copywriting. I find that term what? little slogan? alienating and offensive. “Bonded” implies a financial guarantee of completion or return on investment. This is nothing but EMPTY HYPE.

        I have had it with this manure stealing my time. There’s no denying Republic is cheap, but it’s no great deal. In this country, we provide FREE cell phones for people who are old and/or sick. These simple phones work fine. There is zero need to pay a penny to have emergency telephone service. The only purpose Republic is good for is people who either have nothing important to say or don’t need (or much want) to listen to whoever thinks they do.

        Lose that lame Republic phone . . . or just keep it on a charger for back-up if you are desperate. Or not? You do have a portable back-up battery, don’t you? If you, you understand battery load is NOT an issue anymore.

        BTW, Der Fluch, Baby, as an experiment, while tapping out this little comment I turned my excellent home wiffy off on my phone and watched as a mere ONE-IN-FIVE calls penetrated the jungle of cell signals filling the ether around my home.

        THANKS. Now I know I really do not want Republic amateur hour flakiness cluttering up my communications. So this little trial has not een a waste of time after all.

        [a-n-d . . . how much luck have you had making that recently added “hot spot” feature work? Myself, I fought with it for 20 minutes before i remembered who and what I was dealing with and abandoned it forever.

    • chaddesch

      I may be wrong or misunderstanding, but it sounds to me like a server does all this work apart from your device and then serves up the data to your phone. It doesn’t sound to me like the phone is necessarily switching to one network or the other to retrieve the packets.

    • Anna C.

      Hey! Just wanted to clear up a couple things. You should not notice any impact on your battery life from Bonded Calling. We take care of everything on the back end, so your call quality should be better as it is using the best network possible and patching it when there are any gaps in that coverage. It is already active and rolled out on your phone, so give it a shot and let us know! 🙂

      • rcxb

        I don’t believe its possible to use the cellular radio and the wifi radio simultaneously without increasing power consumption. Maybe it won’t be significant, but I’d hope for an option to turn it off if I see problems. Also, I have a 1st gen Moto E, so I don’t think I can try it…

  • Maniac

    Sounds pretty interesting, can’t wait to try it out.

    • http://www.republicwireless.com ajmaphone

      It’s on your phone right now. 🙂

      • Maniac

        Noticed that already, haha

  • Joel May

    What phones does this feature work with? It sounds great and I’d love to see it on my Moto X 1st gen.

    • bitflung

      according to Republic’s FAQs your 1st gen Moto X will absolutely have this feature as long as you update all the apps and Android itself (to the current latest versions):
      https://community.republicwireless.com/docs/DOC-2829

      quote from that page (at time of writing):

      How can I get Bonded Calling?

      Bonded Calling doesn’t require you to change or adjust any settings. As long as you meet the following requirements, Bonded Calling will work for you automatically:

      You must have a Republic Wireless phone on Android 5.0 (or higher). (This means DEFY XT and Moto E (1st Gen.) users are not eligible.)
      Your Republic Wireless phone must be on Republic App version 2.1.0 (or higher).
      Your Republic Wireless phone must be on Republic Telephony App 2.1.1 (or higher).
      You must also have access to cell data, so phones with WiFi only plans aren’t eligible.

    • Anna C.

      It will! @bitflung:disqus is correct 🙂

  • Jeremy Amaismeier

    @disqus_XnMPUf0L8c:disqus Thanks for the informative article. I’ll reserve judgement until we can all experience how this works, but it sounds promising.

    When you say, “The Republic server listens for both, and takes whichever wins the race,” is server referring to the Republic app running on a phone? Also, what kind of a performance impact does bonded calling being active introduce on a phone? It seems like a lot more than would normally be going on.

    • Anna C.

      The server is on the Republic back end. Your phone is sending the data packets and the server is receiving the packets. It does not have a significant impact on your phone, other than improving your calling experience 🙂

  • Sara Ellison

    How do I know if my Republic Moto X is utilizing Bonded Calling?

    • Anna C.

      So long as you are running the Lollipop operating system, and your Republic and Telephony apps are up to date, you will be utilizing Bonded Calling 🙂

  • lward

    Not sure if this is what is causing issues with my call quality, but i have to turn airplane mode on when i’m home and connected to WiFi. The audio on my 2nd gen moto x just does not work when cell and wifi are both on. i can never get the handover from wifi to cell to work (always have to end the call, switch, and call back). is there something i need to do on my phone to fix this? i do like republic wireless, but the past month has not been good for audio (unless of course i’m just on wifi).

    thanks!
    Liz

  • Myo On Susan Hagler

    Does this work on Moto G first gen?

  • Philip

    Two thumbs up ! I’ve got 2 phones on the 2.0 plan (about $25/month after all taxes and fees, for BOTH phones, not each one, including my $1.75 beta tester discount). Even though I use only about 1000 minutes, I don’t know how Republic is able to make enough profit to stay in business. The only company, I’ve heard of, with a lower price is Freedompop, and only if you pay for an entire year up front. But their system is only half as reliable, and FP has too many inaudible words. Republic interfaces very well with Google Voice. FP doesn’t.
    Using wi-fi saves the carrier money, but Republic’s blending cell service within each call to maintain premium quality, gets my vote.