So this is a new error for me, not seen this in Skype Client logs before. But there it was, SIP/2.0 415 Unsupported Media Type.

The deployment is Two Front End Pools (both Standard Edition) with a single Edge Pool. No Enterprise Voice (yet).

The Problem

When attempting to call a service that’s effectively a Pexip DMZ Cloud Service in New Zealand (called SmartPresence) from the corporate LAN then the call seems to connect but then disconnects, there is no audio or video.

It all works when then the Skype user tries calling the Pexip\SmartPresence bridge from an external location (not corporate LAN).

Troubleshooting

At first glance, you’d agree that this smells of firewall issues. Lets see what the logs say. Heading off to the client logs cause that’s my go to as a starting point for these sorts of issues. I find the call and of course spot the SIP/2.0 415 Unsupported Media Type.

Looking at the negotiation of Media I see that the Skype Client sends all the usual audio and video codec options.

Audio options from Skype client

Video Options from Skype client

On the inbound side from SmartPresence we see that there are less media options (thats expected) but certainly options that match with what the Skype client is capable of.

Audio Options from Pexip\SmartPresence

So it appears that its not so much an unsupported Media type, lets see what the clients agree on using by looking for the results of the candidate negotiation.

Looking for the a=remote-candidates line tell in the client log should show the options both clients agree on.

Wait..there is no a=remote-candidates for this call!

What, so that means that the candidate negotiation is failing to establish a viable path between the the Skype client and the Pexip\SmartPresence service. Taking a closer look at the candidtes on offer I see the below.

Candidates from Skype client

So the Skype client sends options 2,3 and 4 as viable (1 and 5 are direct, thats not allowed by customer strict firewall policies).

Candidates from SmartPresence\Pexip

Looking at the options from the Pexip\SmartPresence service I can see the candidates on offer.. and there it is.

Those are not standard ports!

Since when do we need ports in the 40 000 range from our Edge Server pool outbound?

Right, what does the Pexip portal say with regard to firewall requirements. Searched a while for this info but eventually found the following table

and also this little gem

Solution

Open ports 40 000 – 49 999 for both UDP and TCP outbound from the Edge pool to Pexip\SmartPresence Cloud

Source https://docs.pexip.com/sfb/ports.htm