(High Quality) VoIP on the iPhone

(Regular readers will note that my excessive use of parentheses has now spilled into my titles and first sentences)!

Ahhh Apple... Ahh the iPhone. Regardless of how you feel about this company or their product you can't doubt the market impact they've made over the last couple of years (decades perhaps?). Multitouch (NOT multitasking). App Store. iTunes. There are countless other blogs that discuss these topics so I don't need to. As usual I'm here to talk about VoIP.

For the last ten months or so I've been involved (part time) in another local venture. Voalte (pronounced volt) is a startup here in Sarasota, FL founded by Trey Lauderdale. When the Apple iPhone was announced Trey was working in sales for Emergin, a healthcare IT middleware provider. Trey noticed how incredibly arcane the mobile devices used in healthcare are when compared to this new device from Apple. Once the iPhone SDK was announced Trey knew he had to develop an iPhone application for healthcare. This application became Voalte One.

Voalte One is an iPhone application that provides voice, alarms, and text for healthcare point of care providers (that's nurses to you and I). The complete Voalte One solution is comprised of the following parts:

- iPhone
- Voalte Server (XMPP, LDAP, etc)
- Voalte Voice Server (FreeSWITCH using SIP + event socket)
- An overall excellent customer/user experience (also new to healthcare)

Text messaging and alarm integration are cool but as I've already said, I do VoIP. If you'd like to know more about iPhone development, XMPP, LDAP, etc let me know and I can point you in the right direction.

VoIP in our application is interesting. It's a softphone, technically, but unlike one you've ever seen before. As everyone knows the iPhone cannot run multiple applications. It can't background applications. These are just two of the many challenges introduced when developing a user-friendly, always available, reliable non-GSM phone experience for the iPhone. Simply downloading an off the shelf softphone and installing it on the iPhone is not enough.

We're a startup and we get to do cool things. For example, one of the big differences between VoIP/voice with Voalte One on the iPhone is the voice quality. We use G.722 wideband at 16kHz as our standard voice codec. Why? Because one Saturday (after a long night out) Trey and I were having lunch. I asked him if he thought we should set ourselves apart on something as basic as sample rate. After a little explanation on my part we quickly decided - why not?

As cool as G.722 is it introduces some interesting challenges:

- The iPhone. How are we going to get 16kHz audio from the hardware?
- PJSIP (our SIP stack). Does it support G.722? How does it interface with the audio hardware?
- Hospital PBXs. Voalte One interfaces with the hospital PBX as an ordinary extension. Most of them probably don't support G.722. How/where do we resample to the standard 8kHz used in G.711?

After looking through PJSIP and the available audio drivers for the iPhone we decided we needed to write our own. There were legal and technical reasons and I'm glad we did it. Especially because I didn't have to do most of the work! ;) We also confirmed PJSIP supports G.722.

Voalte has an amazing iPhone developer - Robbie Hanson. Robbie, Ben (Voalte CTO), and I were able to look over the available audio frameworks on the iPhone and pick the best. Not only is it the best overall (it supports echo cancellation, etc) it would provide us the sampling rate of 16kHz we knew we needed.

After working with PJSIP and AudioUnit for a while Robbie was able to write an iPhone audio driver (using AudioUnit, of course) for PJSIP. While working on the audio driver Robbie (along with another contributor) also wrote an Objective C wrapper for PJSIP. These are the raw ingredients of a high quality VoIP experience on the iPhone.

In the months leading up to release we had to deal with a plethora of other issues: push notifications, local ringback, wifi, etc, etc. I won't (and probably can't) describe these issues in detail.

The good news is Voalte has done the right thing and released the core components of this solution as open source.

I'm proud to work with companies that "get it" and are willing to actively participate in the free software ecosystem.

Upcoming Review: Building Telephony Systems with OpenSIPS 1.6

Packt Publishing has once again asked me to review their latest work in the OpenSIPS series: Building Telephony Systems with OpenSIPS 1.6.

My review of the previous edition goes all the way back to when OpenSIPS was called OpenSER. I have another post discussing that topic...

Anyways, I should be receiving the book this week and I should have a review up by next week.