Yet another noob question)

Hi folks,

So, I’m in the process of implementing a VoIP solution here in my office. Small Call Center (12), and 8 admin people. My plan is to use SoftPhones for the CC staff, and Hardphones for the admin.

I’ve been looking at all the different choices for phones. I’d like to be able to use IAX and/or SIP. Would the Cisco 7940G work? I’ve also looked at the SNOM, and Polycom Soundpoint.

Do I need a specific phone to work on IAX?

Little confused here, so any input is appreciated.


Yes, you’d need a phone that specifically supports the IAX protocol if you don’t want to use SIP. Since you want to use SIP, however, you can use any SIP- or IAX-capable phone in your setup.

The Cisco 7940G would work, but you’d really want to load the SIP firmware on all your Ciscos – Asterisk does have support for Cisco’s closed SCCP protocol, but it’s not complete by any means. Getting the SIP firmware requires an additional purchase from Cisco.

Any of the Snoms or Polycoms (of which SoundPoints are one) supporting SIP would work as well.

There are IAX2 hardphones available. The problem is that right now, most of them are pretty cheap and won’t get you the same quality of Cisco or a Polycom would. If you really want to go IAX, I’d recommend buying a couple phones and seeing how they work for you. If you can buy from a company with a liberal return policy, all the better, otherwise there’s always eBay if things don’t work out. :wink:


Thanks for the info. Ok, now I’m REALLY confuzzed! What then is the point of IAX(2) if there are only a finite number of cheap phones out there to utilize it?

When I first started researching this whole thing, I thought…wow…Open Source PBX software…cool…and was impressed when I saw IAX and read about it. Now do I understand correctly that even if I terminate to other IAX servers…my users must have IAX compatible phones as well?

Not sure how I missed this tidbit earlier…


It’s easy to get in over your head quickly when jumping into IP Telephony, so hopefully I can help clear things up.

The big point to understand here is: Phone-to-server and server-to-server are off in their own separate worlds.

Another idea that may help clear things up is that your phones will only ever talk to your server.*

If you want to connect two servers with IAX, you can do that (and I’d strongly recommend it instead of SIP when possible). How the servers communicate with one another is completely independent of how phones communicate with your server. You could connect the servers with a couple tin cans and a piece of string so long as Asterisk knows how to use it. :wink:

The life of an average IP phone is simple: it wants to register with a local server that will connect its calls for it. It doesn’t care how that server (in our case, Asterisk) talks to the rest of the world. It tells the server “hey, I want to call X,” and then the server handles calling X and acts as a go-between for your phone and the foreign phone. Things just happen transparently from the phone’s point of view – it doesn’t need to know anything about where it’s calling or how it’s being done.

It could be an analog phone, a SIP phone, and IAX phone, a SCCP/Skinny phone… as long as it can talk to your server, it doesn’t care. Your server can then use IAX or SIP or whatever to find its way onto a larger network, paying no mind to how your phones are connected to your server.

Here’s some awful ASCII art that may better illustrate what a typical call “looks” like in a simplified manner:

Mic on your phone    ----> |            | ====> Spkr on outside phone
Spkr on your phone  <====  |  Asterisk  | <---- Mic on outside phone
                                 ^             KEY
                                 |             --- audio from original phone
                                 |             === audio from Asterisk
                         Magic happens here

More accurately, here’s what’s most likely happening* in full:

 _______      ______________          ______________      _______
| Your  |    |              |        |              |    | Their |
| Phone |<-->| Your  Server |<<====>>| Their Server |<-->| Phone |
|_______|    |______________|        |______________|    |_______|

(* There are exceptions, but for the sake of Asterisk discussion, they’re really not relevant.)

Gotcha! Thanks! So…to just finish the thought to it’s logical conclusion then…What would be the advantage of using an IAX compatible phone? Is it just to remove the step of the * server converting to SIP?


For your typical small office setup, there’s not a whole lot of advantage. It’s more efficient than RTP (which SIP uses), so you’d have less network traffic.

For more exotic networks, though, or if you have telecommuters or traveling employees who need phones, it’s much easier to get IAX2 working than SIP.