Your Linux Data Center Experts

A while back we looked at SIP software phones. Recently I realized that since I always connect to asterisk servers, I could use the IAX protocol instead of SIP, and it turns out that there are some native IAX speaking software phone clients available for Linux.

Read on for a review of several of them.

So whats so great about the IAX protocol? After all, SIP is the “standard”. Well, voip-info.org has a nice write up of the differences. For the end user, the nice things to note about IAX are that it handles NAT without needing any special handling, and that it's lower overhead.

On the server side you need an asterisk server to connect to. You can setup your own, or you can even connect to something like Free world Dialup or look at the (long) list of commercial providers that allow IAX connections.

On the client end, there are several clients available for Linux:

  • The iaxcomm client library is the basis for most of the clients.
  • kiax is a KDE based client that uses iaxcomm
  • qtiax is a QT based iax client.

There are also a number of windows and macosX IAX clients.

Initially I ran into an issue where the start of a call would be great with either iaxcomm or kiax, but then the delay would get longer and longer. After a while it would get to be 7 or 8 seconds and disconnect. It turns out that enabling the iaxcomm automatic gain detection was the culprit there. I recommend you never enable that option.

Of the various clients I tried, I like kiax the best. It has a number of nice features:

  • It looks nice.
  • It keeps a calls log
  • It can connect to any number of IAX servers. So, you can connect to a work server, a home server, and a long distance interface to the PSTN ( Plain Simple Telephone Network) at the same time
  • It has a nice log window, also allowing statistics like lost packets and jitter and delay to be displayed.
  • There are rpms (including src.rpm) available

So, how's the sound quality? Pretty darn good. Connecting to either home or work asterisk servers, or the IAX providing service for long distance seemed to work pretty well. Better quality than the SIP software and also able to connect to all of the services at the same time from one instance.

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