 | As many organizations around the world are adopting Microsoft Teams as their enterprise communication and collaboration platform, the demand of IP desktop phones continues to be strong as companies replace their aging PBX phones in place of newer Teams certified IP Phones. Teams calling plans are now available in more countries and Direct Routing can be used virtually anywhere with a certified SBC. To ensure the best possible call quality when deploying Teams Phone system, QoS can be implemented so that the network is optimized for audio and/or video calling. Microsoft provides detailed documentation on how to implement QoS in teams and in this blogpost, we look at how it works with Teams certified IP Phones such as the Poly CCX family shown on the left. Click here for the complete list of devices. |
To begin we first enable QoS via the Teams Admin Centre under the "Meetings" section go to "Meeting Settings". There we can find a "Network" section where we can enable or disable QoS along with other important parameters as shown below:
The recommended setting is to specify the port ranges for Audio, Video and Screen Sharing, each with 20 ports. Once these settings are saved, they will be applied to Teams clients including the certified IP Phones which are running the Teams apk on top of Android OS. We proceed to power up our Poly CCX400 and sign-in on the phone using a regular Teams account. Next we start Wireshark capture on the network interface of the phone and proceed to make 2 types of calls - point-to-point call to a PSTN number via Direct Routing, and joining a meeting as a audio participant.
Point to Point call from Teams phone to PSTN via Direct Routing:
Here we are simply calling a cellphone number and lets analyze the wireshark trace. We can see there are 2 audio streams in the packet capture, from the phone's IP 192.168.138 to Teams' IP 52.115.168.51 and vice versa. The IP Phone uses the port 50008 which is indeed between the audio range specified above:
Point to Point call from Teams phone to PSTN via Direct Routing:
Here we are simply calling a cellphone number and lets analyze the wireshark trace. We can see there are 2 audio streams in the packet capture, from the phone's IP 192.168.138 to Teams' IP 52.115.168.51 and vice versa. The IP Phone uses the port 50008 which is indeed between the audio range specified above:
Next lets look at the QoS markers, which in this case is the DSCP value in the UDP packets. We can see the the UDP packet going from the IP phone to Teams is marked with a value of 46 Expedited Forwarding which is fixed for Audio packets and cannot be configured:
On the other hand, the UDP packets coming from Teams to the IP Phone do not have DCSP markings and this is expected:
Joining a meeting from IP Phone as meeting participant:
Here we are simply joining a scheduled Teams meeting via the phone as an audio participant and analyze the wireshark trace as before. Since its a meeting hosted on Teams, the destination port for audio is fixed at 3479 while the phone itself utilizes a port within the same range as before and packets going out from the IP Phone to Teams are marked with DSCP value 46 Expedited Forwarding:
Here we are simply joining a scheduled Teams meeting via the phone as an audio participant and analyze the wireshark trace as before. Since its a meeting hosted on Teams, the destination port for audio is fixed at 3479 while the phone itself utilizes a port within the same range as before and packets going out from the IP Phone to Teams are marked with DSCP value 46 Expedited Forwarding:
And finally packets coming back from Teams to the IP Phone do not have any DSCP marking as expected:
In conclusion QoS settings are easily configured in the Teams Admin Center (TAC) and applies to not just IP Phones but all Android and iOS devices in general. To achieve the same DSCP marking on the Teams client on Windows PC, additional steps to implement Qos via Group Policy (GPO) are required as described in the Microsoft documentation.
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