I’m trying to write a voip app for Android, using the Android SIP API (Yes, I know this only works with some Androids with version 2.3). I want calls to be routed through an Asterisk server. The calls also need to be encrypted. A problem exists where Asterisk and the Androids need to be on the same subnet (otherwise no audio is exchanged). There is a nice blog post I found at http://blog.harritronics.com/2011/06/android-gingerbread-and-asterisk-pbx.html describing the situation for those that are curious.
I’m looking to setup a VPN solution as discussed in the article as I figure this could solve the NAT issue, along with encryption. My first thought was to use OpenVPN since there is a pretty active community and the software looks pretty nice. However, after further inspection, it seems that I can only have 2 clients active on the VPN server at any given time (for the free version). Each additional client connection is $5. In short, I’m wondering if a scalable free solution exists. I would like to be able to connect somewhere around 100 android phones to this VPN to communicate with Asterisk simultaneously.
Also, I have done no VPN work previously. I’m wondering can I simply use the VPN configuration within the Android Settings? Or does there need to be an additional application? I saw that OpenVPN had a client solution for Android that only worked if the phone was rooted – this is not an option, as they are not my phones. Any advice would be greatly appreciated.
Thank you!
Not sure what you’ve been looking at, but OpenVPN certainly does not have any restrictions on the number of clients. Anyway, as you have found out, OpenVPN is not supported by the default Android distribution, though it is integrated in CyanogenMod. Android also has a built-in VPN client however, so you just need to find a server that works with that. As of 4.0 (ICS) it is also possible to write your own VPN implementation without rooting the phone.
BTW, the audio problem only arises if the phones are NAT-ed (e.g., connected via WiFi to your internal router, etc.). If the have global addresses, there should be no problem. If you connect over 3G that would depend on whether your carrier gives phones actual global addresses.
Another alternative is not to the Android SIP stack. There are other solutions available, and they might not have this restriction. Check sipdroid, it open source:
http://sipdroid.org/
Yet another alternative is to not try to write your own app, just use sipdroid 🙂