Asterisk and geographically dispersed offices

I am planning to start using asterisk in our company, which have about 30 small offices. But I have some fundamental questions about planning and deploy.
My opinion about it: use one central asterisk server with user’s data in database + self-written web-interface. Each office will be connected to central office via tunnel.
So my question, is this solution appropriate? Or maybe I need addition asterisk server in each office? I need some help in this area: web link or some words.


Depends on the nature of the business, i.e. how much locality there is in telephone traffic.

I have this thought too.

This is freight transport company. Each local office consist of warehouse, about 5-10 employees and about 1-2 tel. numbers. Therefore I think to use topology with one main server and tunneled clients. Offices will be connected via IPSec or OpenVPN (local office <-> main office). What do you think about it?

And where is limits in simultaneous_calls/phone_numbers/number_of_employees/etc. where I should consider use in local office own asterisk server and communicate it with asterisk in main office?

I think that your plan is good. Use high quality grade routers so your IPSec links will not be dropping all the time (if VPN tunnel will not work, telephony won’t work) and a good ISP that does not have a lot of downtime on their connections.

It is sensible to use a local PBX on locations that have a lot of internal calls and/or can not afford any downtime on the telephone system.

About the limit of simultanious calls - I think the limit will be the internet connection speed. When you do the calculations consider that a single telephone call takes up arround 100 kbps in both direction (it takes up arround 80 kbps, but I always like to be on the safe side with using 100 kbps in the calculations).

Agree with you too.
And the last question. Possible, in future, I will need in local office own Asterisk server. For me it’s not a problem to join two servers. But if such offices will be 3 or more… How join 3 or more servers in one VoIP system??
In my opinion, now during development stage I must provide for such scenario.
So, this is my thoughts: I must have Asterisk with user’s data in DB in main office and when I need add one more server in local office I just setup new Asterisk with slave DB (DB is replicated from main office). Is my thought correct?