Tuesday 28 October 2014

Hacking our way through Astricon

This year I was speaking at Astricon for Truphone Labs (you can see my slides here if you're interested).

The week before Astricon I was invited try out respoke, a solution that allows you to build a WebRTC-based service.
They provide you with a client JavaScript library, and you need a server account (with an app ID and secret key) to connect your application to the respoke server and allow clients to communicate with each other.
This is an intuitive approach. As a service developer, you pay for the server usage, and you do so depending on how many concurrent clients you want.
I got a testing account, and started trying out the JS library. The process of building a new application was very straightforward, and the docs guided me towards building a simple app to make audio calls, and then video calls as well.

Soon I started thinking: respoke is from Digium, right, and Digium develops Asterisk. How is it possible that respoke and Asterisk cannot interconnect? What I’d like to do is place a call from web, and in some circumstances route it to a SIP client, or a PSTN line, or mobile phone.

It turned out that my expectation was quite justified: 36 hours before the beginning of the Astricon Hackathon, Digium announced chan_respoke, a new module for Asterisk (13) that allows Asterisk to connect as a respoke client and communicate with JS clients.

So that was the good news. The bad news was that we didn't have any time to prepare before the Hackathon, so we had about 8 hours to get up to speed and build something… sexy!
The other service that the Astricon Hackathon was encouraging to use was Clarify, which provides APIs to upload audio recording and is able to detect some specific “tag words” from the recordings.

Among the people discussing the formation of a team the most complete and compelling idea, and one that probably did require all 5 people working together, was GrannyCall. You can see some details here, with the list of team members.

GrannyCall was thought as a system for kids to call their granny (or daddy, mummy, etc.) from a simple web page, and get a score depending on how their vocabulary was appropriate and rich.
For example, we wanted to give some positive score for words like “love” or “cookie”, and perhaps a negative score for… well, you can guess some words that would score badly for a kid talking to his/her granny.
The project was quite ambitious, because the originating call would have been from a web page built with voxbone’s webrtc library, reach Asterisk over SIP, and then ring the granny on a web page built with the respoke client.

We used an Ubuntu VM from DigitalOcean to host Asterisk and the web servers (nginx) for the two web pages, and an external web server to interconnect to the Clarify APIs for uploading the recordings (with the desired tags).

Asterisk needed to be version 13, and chan_respoke was built and configured. The DigitalOcean box was on public IP so there wasn’t the need for any specific networking.

The part “kid to voxbone to asterisk” allowed for some preparation and went smoothly right after the time to build the web server and upload the client page.
While Asterisk was being built and configured, we built the granny web page with the respoke library. Again in this case it was quite easy and quick to have a call between two respoke clients, peer to peer, just to test the client application on the browsers.
The tricky part was originating the call from Asterisk to the granny web page, using chan_respoke.
For the sake of testing the connection and media establishment, we made some calls from the respoke client to Asterisk, hitting an announcement and an echo test. That worked almost immediately, and it was great!

Now it was the key moment: can we do the full flow (kid – Voxbone –asterisk – respoke – granny)? In terms of establishing the call, i.e. signalling, that worked too just after a few tweaks to chan_respoke’s configuration. But what about audio?

It turned out that there were some problems in the ICE negotiation between the respoke client and Asterisk: we had audio only in one direction. We were using Chrome at that moment, and moving to Firefox didn’t help, so we did think there could be possibly a bug in the libraries.
Considering the maturity of the libraries, this looked completely understandable, and the respoke guys spent a lot of time helping us investigating the problem and trying to find a proper solution before the submission deadline (this resulted in a patch on the server side being applied the next hours).

Honestly, I was happy that the Hackaton was scheduled for only a relatively short time as eight hours: would it had been any longer, we probably wouldn’t have dinner or had a proper sleep (and the 8 (or 9) hours jet lag was not particularly helpful!).

At submission time, we didn't have two-way audio. Also the debugging ate precious time to prepare the presentation to the judges, and this could be the reason why we weren't awarded any prize. Honestly, given the intensity of the effort and the complexity of the project, I was hoping for at least an honorable mention, but I hope we can gather again the same team in a different occasion and bring different results!

Jokes apart, it’s been an extremely useful experience. No documentation or remote communication can replace the live interaction and working on a proof of concept – in particular if you have a crazy deadline and the body full of caffeine and sugar (and a few hours' sleep in the last 36 hours).

Of course we took some shortcuts, like removing any firewall from the host, use a common linux user, authenticated via password and not SSH keys, edited files in place, etc. We did those things knowing they weren't best practices but aiming to complete a proof of concept as quickly as possible.

The takeaway from all this is very simple: if you’re developing a new technology, or a new solution oriented to developers, do whatever you can to involve the developers in a productive, challenging way. Hackathons represent a great solution, even if confined within a company, department or team. The excitement and the feedback (and debugging) you'll help to generate will have a tremendous value.


  1. Giacomo,
    This is a great write up on the hackathon! We were very happy with the participation and the event as a whole. One of the concepts we discussed as we debriefed the event is that we could have been more overt with a "hack at your own risk" message in regards to chan_respoke with Asterisk. We were pleased to be able to get the code released in time for the hackathon, but knew that it could potentially cause problems because it was so new.It was gratifying to be able to track down bugs and get them fixed on-site at AstriCon (unfortunately too late for the hackathon.) There were so many terrific apps, including GrannyCall, I wish that we could have awarded prizes to everyone! I completely agree that the excitement and feedback from events like this have tremendous value and I'm looking forward to the next one :)

  2. Respoke and consequently chan_respoke will be announced soon as dead..next astricon i have been told..
    Have you got any idea for the reason?


About ICE negotiation

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