Advice/confirmation of Setup

I am planning a new Asterisk system for my office of around 30-40 extensions at the mo, but cope with more extensions in future. Most traffic will be sip unless the internet fails then i will fall back to 4 ISDN channels

Intended Hardware Setup:

2 asterisk servers connected by IAX on LAN
each Pentium 945 3.4ghz dual core with 1gb ram & a 3ware hard disk mirrored array.
Each server to have 1 sangoma a101 card connected to a 2 channel single isdn line.

Is it easy/possible to have a sangoma card in each server to utilise all 4 ISDN channels & auto switch over to this if our internet connection drops? So i am lloking to use all isdn channels no matter which server the user/handset is connected to…

Also will i run into problems if install a TDB20B- 2 x fxs card in each server along with the sangoma card? (as i have read about issues of having more than 1 card in a server…)

Obviously from the dual setup i am looking for redundancy & reliability…

Any comments appreciated!



No-one got any advice?!?

I particually interested to know if i do an iax trunk between 2 servers - if i can fully utilise both ISDN BRI cards.

Example: 4 people phone out from 1 server - 2 calls go out on from isdn card in server 1 & 2 calls go out via 2nd ISDN BRI card in server 2 via IAX trunk??



the sangoma a101u is a PRI card, and will handle up to 30 channels. if you’re using a BRI interface, you want BRI cards. i’d suggest searching the wiki for suitable hardware (i’ve yet to do a BRI install !).

also, for this number of extensions, why are you running 2 servers ?

i’ve not had problems with running multiple cards in one server, although i’ve tended to use the same manufacturer … sangoma hardware seems to be a bit easier to use with mainboards that aren’t particularly clever. you need to watch out for gotchas when setting up your spans though.

Thanks for the reply.

I want redundancy - if one one server fails i want another to take over, it is for a business - cannot afford to have telephone system down for 5 mins. Anyway servers/hardware are cheap, so why not do it??

I am getting 2 x ISDN 2e lines - total of 4 channels.
I asked a UK reseller if the A101 would work with ISDN2e (BRI) - they said yes. BT will only give you a ISDN 30e (PRI 30 channel) connection if you want 8 or more channels out of the 30 as a start. I think i can get away with 4 channels to start, hence the 2 x ISDN2e lines going into 2 x A101 cards (also gives room for expansion if we need it…) These 2 cards will only be used if the VOIP service/internet connection go down…

Can you see a problem with this setup?



who was the reseller ? i’m interested to see if the A101u works with a BRI connection … there aren’t that many BRI interface cards around … not without spending a fortune, so it would be good if it works !

unfortunately, just having 2 servers online isn’t going to give you full redundancy, or anywhere near it. if you split your registrations then if one server fails then it takes all the peers with it.

in your position i would get the ISDN30 install with 8 channels (if you have alternative providers available, you can try getting an install without having 8, YMMV) and have a spare box ready to go. redunancy is quite a hot topic, and you can get it in many forms, but without spending a lot of wonga you’re going to have some downtime :frowning:

I realise that there would be some downtime (not going to get auto-failover) if 1 server failed.

But could I not have the other/failed server’s users registration data remmed out in the configuration of the 1st server. Thus when a sever fails - just un-rem the extra user info & re-start the server?

regards BRI/PRI reseller:


Yes, Sangoma cards work world wide including the UK.

If I can be of any further assistance please do not hesitate to contact me.

Best regards,

Alexis Argent

VoIPon Solutions
Head Office
P.O. Box 2124

Tel : +44 (0)1245 600 560 Ext. 204
Fax : +44 (0)1245 600 030
Email :
UK : norm://

-----Original Message-----
From: Barry Nelson
Sent: 25 August 2006 11:22
To: VoIPon Sales
Subject: Enquiry from VoIPon

I assume the Sangoma A101 PRI ISDN Card will work fine with a UK ISDN2e connection?

What do you think - was their answer a bit vague? Has no-one else ever used the A101 on a ISDN2e then?



to be honest, if PRI cards worked on BRI interfaces, there wouldn’t be a need for some of the BRI products out there … e.g. … 8d83c2de44 is the new Digium Quad-BRI card.

OK just a silly question. Coulndn’t you just use the TDM40B card from digium in each server and setup a phantom IP address in each card using a router to diable one of the IP addresses as a duplicate then mirror the registration/configuration between the servers and split your anolog lines so they connect to both TDM cards? Seems like you would then have the redundancy you are looking for. What you are describing seems like load balancing not redundancy to me. You wouldn’t have to actually rem out any of the sip configuration and if you use Cisco phones (While I know they are expensive I still use them) then you could set up half your extensions to use BoxA as a primary and Box B as a backup and the other half the other way around that way if either box fails you still have all your extensions working. Then in your dialplan you setup the other box as an IAX switch and dial the Extension on both boxes from either box when you want to ring it. You would get alot of failed calls this way but it should work.