Skype for Business 2015 – Skype for Business 2015 Mediation server SIP Trunk Ports

Let us talk about the Skype for Business 2015 Mediation server; keep in mind this can apply to Lync 2013 as well.  One of the areas when talking about enterprise voice that will surely come up is “SIP Trunks”.   So let’s jump straight into an area that can be very confusing when we start to talk about listening and sending ports for the Skype for Business server side regarding the port trunk configurations.  

I will cover the following areas for the trunk configuration:

Listening port for IP/PSTN Gateway 

The Skype for Business 2015 Mediation server is going to look to send SIP (signaling) and Media (audio) through a certain port in a SIP trunk created to the IP/PSTN gateway or a specified port range on the mediation server.   That default port for TLS is 5067 and the default port for TCP is 5066.   You can specify a TCP port range if you wish, such as 5070 – 5090.  We are going to keep it simple for the sake of the article and going to go with a port range of 5068 – 5068. So what this means is that the Skype Mediation servers is not going to be on another port for TCP using SIP and Media from its SIP peer next hop which in this case is the IP/PSTN gateway other than 5068. 

Note:  Let’s not get caught up on which IP/PSTN Gateway we are using, it could be various PBX’s such as Cisco, Avaya, Nortel or a gateways such as Audio Codes, Dialogic or, Sonus.   

The next hop IP/ PSTN Gateway is going to send SIP and Media to the port we selected for this portion of the trunk configuration.  Therefore, what this means for the information you tell the telecom person is that you will be sending them TCP/SIP and Media over port 5068.  In addition, vice versa this means that the telecom team should anticipating receiving TCP/SIP and Media from the Mediation Pool over port 5068.

How does this differ if you have a port range?  Nothing at all, just know if you had a range of let’s say 5070 – 5090, then you are telling your telecom person that you can send TCP/SIP and Media through that particular range; but on this particular trunk you are going to send SIP and Media through a particular port that you specified on the “Listening port for IP/PSTN gateway” section of the trunk configuration. 

The Mediation server can handle multiple connections over the SIP trunk that are created to the IP/PSTN gateway.  In this example, we are saying that the PBX is listening on port TCP/5068 and the Mediation server is listening on port TCP/5068.  Besides these ports the Mediation server uses ports 60,000 – 65,536 (UDP) for the audio traffic as well. Make sure to open firewall ports 60,000 – 65,536 between the Mediation server and the PBX. 

Associated Mediation Server Port

Now contrary to the “Listening port for IP/PSTN Gateway” the “Associated Mediation Server port” is the complete opposite. Which means that Mediation Server listening (not sending) for TCP/SIP and Media on the specified port which in this case is port 5068.  

When a PBX sends, TCP/SIP and Media to the Mediation server, typically the telecom team is going to ask you what port do you want them to send traffic to you on.  This is where you specified in figure 3 below what port that will be.  Once again if you have a port range that is fine, but keep in mind that for each trunk you have to specify a certain port to send and receive the SIP and Media traffic on. 

Mediation SIP Trunk Ports Simplified

TCP/SIP, Media listening, and sending ports can be confusing if you let them be.  At the end of the day, its two devices trying to talk to each other and they are asking on which port they should send traffic on to each other. Unfortunately, there is no room for vagueness in this area; we cannot just say, “Setup any protocol TCP or TLS you want and send the media to any port or ports you want, I will be listening and waiting for it….”   If you do have a conversation like that, please be sure to drop me a line for I sure would like to listen in on that dialog.