Connecting Asterisk to Skype

I’ve been using Asterisk for years and never really wanted to use Skype, but since many of my friends do, I decided to have a go. It was quite unthinkable to use Skype separately from Asterisk, I mean I have all of my communication unified through Asterisk box, and now this thing called Skype had to be exempted from the rest. No way. So I was looking for a way to connect them. Skype uses proprietary protocol for communication, and the company DOES NOT ALLOW reverse engineering. Therefore, there was no “clean” way of making a Skype channel for Asterisk, like it was done with Cisco’s Skinny protocol. Well, how do we connect then?

There are two possible approaches: hardware and software one. Hardware approach would require some “Skype to phone” adapter “thingy” that connects to Windows PC via USB, and has FXO and FXS, through which it then connects to Asterisk via Sipura 3000, or what have you. I excluded the “enterprise level multi-channel skype gateways” because they are too expensive. I mentioned Windows PC because I had one up and running 24/7, as described in the previous post.

Available software

I decided upon software approach, since I did have available Windows PC, and didn’t want additional “Skype thingy” and addional Sipura. Here are my choices:

• ChanSkype, Asterisk channel driver for Skype. It sounds great but has one major flaw: it requires X server and I want my Asterisk box to run clean without any additional burdening services.
• PSGx, Personal Skype to H.323/SIP gateway. I have been using it for a while, and it turned out to be buggy and unreliable.
• Uplink Skype to SIP adapter is what I am using right now.

Windows installation

You can download Uplink Skype to SIP here.

When you run the setup program you get a dialog like this:

Then you just let Windows install the unsigned drivers. These audio drivers are the heart of the program. The program sets up these drivers to work as Skype’s headset, and then translates the sound coming from them into SIP packets:

As shown in the figure  (Skype audio settings), the sound coming from you, through the microphone, is getting into SIP packets via Uplink’s sound driver, and vice versa for the sound of the speaker. There are similar hacks with the actual microphone and speakers, that is hardware ones, to find out more check out Grynx’s blog.

Uplink settings

Account settings:

• SIP number and password : your Skype number/nickname and password that are the same as in sip.conf.

• Server: Asterisk IP address.

Network settings:

• Listening local port: default for these settings is not the same as Asterisk’s default SIP and RTP settings, so pay attention.
• Public IP address of your Asterisk box..
• External SIP and external RTP also differ from Asterisk’s default settings.

Asterisk Skype2SIP configuration

here’s my configuration:

sip.conf

[tokenskype]
type=friend
host=dynamic
nat=yes
username=tokenskype
secret=tokenskype
canreinvite=no
insecure=very
dtmfmode=inband
disallow=all
allow=alaw
context=incoming_skype
callgroup=2
pickupgroup=2
canreinvite=yes
qualify=yes

extensions.conf

exten => 711,1,SetCallerID(${MY_ID})
exten => 711,n,Dial(SIP/echo123@tokenskype,40,rwW)
exten => 711,n,Hangup()

Here you see extension for Skype’s echo test. Buddies should be added the same way.

Putting it all to work

After everything is installed and upon starting Skype2SIP you should see something like this:

And if you do “sip show peers” in Asterisk’s prompt:

Calling test echo extension:

and Uplink’s screen shows (talking for 52 sec, then hanging up, from 9:41 to 10:33):

Now just add a few buddies, give them extension numbers, and you’re set to talk…

Just a few final words:

• I made a context for incoming Skype calls “incoming_skype”, as you see in sip.conf excerpt . There you can customize it to dial a specific phone, softphone, send e-mail or whatever…
• Skype video calls can not be routed through Asterisk, but Asterisk is capable of conducting video calls, which is an entirely new topic…

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