Medium size installation, need advice


Just started a new job as a Linux system designer/admin and I have taken on the project of building a Asterisk based phone system for two offices. I have only ever built a small home Asterisk installation with a load of softphones and an external sip account.

We have two offices (one main, where the main server and incoming phone lines will be located)

This is my guess of what our spec will be (should be?):

  • Two incoming lines from BT two different numbers (Is that the best way, can we have multiple calls on a single line?)
  • One main Asterisk box to accept these connections, all calls will first go to the reception IP phone
  • A load of softphones on computers and IP phones on desks (I don’t need help with that bit)
  • The second office will have an internet connection, have its own asterisk box and will piggy back of our main one with the phone lines

Also here is my diagram in PDF:

Really my main question is with the BT lines, what can I get?
Second does it look like its all do-able, with the second office internet link? (I have time)

Thanks for any advice you can give me. :smiley:



Not really medium sized is it 11 handsets in total ! why not just host the second sites handsets of the first site?

Not sure what you mean ? do you mean card or what type of lines ?

if its card then a tdm410 really is the answer.

I would also set it so that if you do use 2 systems the second site breaks out locally for its calls.

Ian Plain


Ok medium for me, like I said, I have never built a system with physical handsets before…

It would be better if we did not have a second server, how would desk IP phones connect to the Asterisk server in a different location?

About the lines I was asking what type of card (so thanks, we will go with one of those from digium) but also is having two analogue lines the best way to build a system like this. In the UK are there any other methods of getting multiple lines (ie. multiple calls in/out of our network at once?)



If your internet connection is of sufficient quality and bandwidth, you could use a SIP provider for all incoming and outgoing calls and do away with the physical phone lines and hardware cards


We get about 6.78 down and 0.65 up, so I’m not sure. It would be nice if we did not need the cards and the physical lines.


G.729 is pretty efficient. Your upstream speed looks like the limiting factor. It depends of course on how many simultaneous calls you plan on, and what else the connection is being used for.



Ok, Bit mean of me. as to lines im assuming you will be having a seperate DSL for the voice traffic so you can just use voip lines, No need for BT lines at all.

Use gsm or g729 licences to compress the calls a bit.

As to site to site connections, Just register the remote sets against the main server.

twitter @cyberco


Understanding the bandwidth requirement is critical, which means understanding how many concurrent outbound lines are to be supported. In my experience G729 codecs are effective: if this encoding can be done at the handset \ ATA, then this will lighten the computational load (another key consideration). Take a look at this last link in my signature for G729 bandwidth usage (1 line).