FreeSWITCH minimal installation and module selection

Question

As someone who is very new to the opensource PBX projects like Asterisk and FreeSWITCH, I am grappling with some information overload. Have read the basic FreeSWITCH docs on Wiki, but still have few questions. Since I am not very familiar with the terminology, I will try to use close approximations.

Trying to create a small/minimalistic build of FreeSWITCH, that needs to run on an rather old laptop (Celeron 1GHz, 512MB RAM, 20GB HDD, already running Debian "Wheezy"), and set it up as a 6-port GSM-SIP/Jabber gateway. So, by "small" and "minimalistic", I mean one which doesn't have modules/optional-software that is not absolutely necessary (e.g. no need for IVR announcements, or Skype integration) -- to keep memory footprint smallest, and occupy less hard-disk real-estate.

The rough idea is to have 6 GSM ports (via 'GSM-open module', similar to chan_dongle) towards public telephony network, and about 60 SIP extension, and support upto 6 calls involving GSM ports, and about 6 SIP-SIP calls (intra PBX), on this setup. I have read that the CPU overhead of GSMopen module is pretty low, so I am guessing this is possible.

1. Can someone confirm this to be a realistic goal?
2. What might be the minimum set of modules to select for minimalistic build?
3. For modules not chosen during initial build, can those be added later? If so, would it require me to rebuild FreeSWITCH completely, only the modules, or that everything would be built, but only configuration changes would be required to ensure that modules are loaded, and configure?
4. Is there any rough estimate of what might be the maximum call-rate that could be supported in such a configuration? For SIP-SIP calls? Given the underpowered processor, and little RAM (as per modern standards), I am guessing that both shall be bottlenecks, but adding RAM might still be possible (even if costly and difficult).
5. I have read that "hooks" can be created using Lua/Python/Java etc.. However if someone share share few examples of what-all is possible using such hooks, it would make the concept clearer. Can one hope to write an application like "missed call log" or "redirect on no answer" using these hooks?

Answer 1

Can someone confirm this to be a realistic goal?

Yes, this is quite realistic. You need to target as little as possible transcoding, because that's where CPU resources are needed. But even with a 1Ghz Celeron, 6 transcoded sessions seem quite realistic. But it needs testing :)

What might be the minimum set of modules to select for minimalistic build?

Just start with the default list of modules, and add gsmopen (I have no experience with gsm gateways, can't help with that part). The memory footprint is pretty low, and you may need some of those modules later.

For modules not chosen during initial build, can those be added later?

as far as I remember, Wiki describes this process. You edit modules.conf and make the specific module.

Is there any rough estimate of what might be the maximum call-rate that could be supported in such a configuration? For SIP-SIP calls? Given the underpowered processor, and little RAM (as per modern standards), I am guessing that both shall be bottlenecks, but adding RAM might still be possible (even if costly and difficult).

It really depends on complexity of your dialplan. Each context consists of a number of conditions, which are doing regexp match on channel variables. So, the more complex your dialplan is, the less CPS you get. But for a 6-channel gateway, I don't see this a problem. GSM network will be much slower than your box :)

I have read that "hooks" can be created using Lua/Python/Java etc.. However if someone share share few examples of what-all is possible using such hooks, it would make the concept clearer. Can one hope to write an application like "missed call log" or "redirect on no answer" using these hooks?

You can control every aspect of FreeSWITCH behavior with FreeSWITCH. There are even examples when the complete dialplan is re-implemented by an external program (Kazoo does that).

The simplest mode of operation is when your Lua/JS/Perl/Python script is launched from within the dialplan: then it receives a "session" object, and you can do whatever you want with the call: play sounds, bridge, forward, make a new call and bridge them together, and so on. Here in my blog there's a little practical example.

Then, you can build an external application which connects to the FS socket and monitors the events and performs actions on active calls.

Also, it can be done in the opposite direction: you run a server, and FS connects to it with its socket library.

Also, you can have an HTTP service which delivers pieces of XML configuration to FreeSWITCH, and it requests those on every call (this would be the most CPU-intensive application). This way, you can feed FS from some internal database, and build fault-tolerant systems.

I hope this helps :) You can also find me in skype if needed.