SIP/2.0 415 Unsupported Media Type

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.

unsupported media

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).


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

Snooper 01

Video Options from Skype client

snooper 02

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

snooper 03

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

snooper 04

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

pexip 01

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

pexip 02

and also this little gem

pexip 03


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



About Paul B

My name is Paul Bloem and I am employed at Lexel Systems in New Zealand as a Principal Consultant for Unified Communications. I have been working on enterprise voice solutions for over 20 years. My first 10 years were spent working for a Telco in South Africa (Telcom SA). This is where all the groundwork happened as I was exposed to just about every aspect of telecommunication you could imagine. I develop an interest in PBX technologies and eventually became the go-to guy. Next, I had a 10 year run at Siemens South Africa, most of my time there was as a Technical Trainer. During this time VoIP hit the world stage, I had the privilege of introducing VoIP both as H.323 and later SIP across the Siemens HiPath 4000 solution stack. In 2008 I immigrated to New Zealand with my newly attained MCSE, I was ready to go where no PBX Techie had gone before. I was employed to explore OCS 2007 and that was pretty much the beginning of the end for me. I have been working on OCS and Lync ever since. My current role focuses exclusively on Lync and associated technologies.. That includes pre-sales, consulting, architecture and design, training and support. I even get to play in the development space from time to time - focus on play ;-) I was nominated as a Microsoft VTSP for Lync early in 2013 and also awarded Microsoft's MVP award for Lync in 2014.
This entry was posted in Firewall Rules, SIP, SIP 415, SIP/2.0 415 Unsupported Media Type and tagged , , . Bookmark the permalink.

2 Responses to SIP/2.0 415 Unsupported Media Type

  1. Baaskar R says:

    Good one, thanks for sharing!


  2. Sean Boss says:

    Good find Paul, thanks for sharing!


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