Commuication between main server and and offsite server

We have an asterisk server with a T1. We will soon have some new sites. What i was thinking is : Setuping a new * Server at every new sites and using the IAX2 protocol between the site and the main server. I have a few questions :

1- Is it a good Idea ? Should I use SIP instead of IAX, or mayby i should not even put server at the new sites but only the phones.
2- What kind of internet connection I will need if I expect the new sites will not have more than 4 calls at the same time ?
3- Any other thing !

Thanks for reading and for any awnsers !

1a) depends - how many phones are at each site?
1b) IAX2 routes much better because there aren’t as many NAT issues. If you setup a VPN between the sites then SIP will work fine.

  1. anything 512MB each way or faster will be more than enough for 4 simulateneous calls with any codec.

  2. depends on answer to 1a

1 a) It depends but … an average of 4-5 phones …

And I won’t use a VPN.

You could go either way.

SIP Phones Only at Remote Office


No Server to Maintain

If internet connect at branch office or main office goes down the branch office phones dont work at all anymore (not even to call across the room!)

Firewall setup can be a pain (or not allowed at all depending on how strict your admin is)

Asterisk Server as Remote Office

Phones work inside the office if internet connection goes down

Can setup a backup POTS line for external calling for emergency use

Can use IAX for calls between locations (easier to route)

More expensive

Server that needs periodic attention at remote location

I am sure I am missing something but its a start. Good Luck.


IAX2 is the simplist and using GSM codec you can have all your phones in use at the same time. Using a VPN will increase the bandwidth used.
As an example a main office with 80 extensions with ISDN30 in feeding both sites is linked to a second site with 15 users, The main site has a dedicated 800K sdsl and the second site has a 2M/800K adsl and using IAX2 and GSM codec for intersite and ulaw for pstn they have no issues with quality.

If your sites are going to be as small as you say, then VPN and sip phones may be te way to go. Or even a sip/fxs gateway


I would put a very small asterisk server(astlinux on a soekris) it is a very small no moving parts installation this way. no bells and whistles… not sure if 1.4 can run on a soekris but the latest 1.2 can. with an FXO card (x100p) in the satellite office with SIP phones…

this way if the internet connection drops your phones can call out on that 1 line and also call each other…