Diagnosing Elusive Issues – How Port Changes on Public Facing Network Devices Impact Teams Calls

Teams calls are highly sensitive operations and dependent on the smooth operation of every aspect of the user’s device, audio/video equipment (headset/webcam), local network, ISP and Microsoft 365 environment. It’s a chain of elements and sometimes things influence your user’s Microsoft Teams call quality without it being obvious or reasonable that they do. Figuring out what causes issues when they arise can therefore be really cumbersome and even impossible in many cases as it involves many different systems, logs and analytics in dispersed locations.

With OfficeExpert TrueDEM we offer a unique end-to-end insight into all aspects that can influence a call. Even the more obscure that would otherwise be impossible to detect. Let’s look at an example.

At one of our customers we noticed that the public port sometimes changes for users during calls. This is the outward facing port used to route the Teams call data from the Firewall to Microsoft Teams. The port is negotiated between the firewall & Microsoft Teams based on traffic, availability and type of traffic and normally shouldn’t change when set while the user is in a call. However it is changing on a regular basis for several users in this organization.

Network Settings

Other network settings remained the same:

Only the public facing port suddenly changes, as is visible in the example call below at 3:36:

Looking at the various metrics for the user and the call, we quickly identified that the user’s Audio RTT (last column) increased to a higher level:

average Round Trip time on Audio on the original and new port:

That’s  ~50% increase on the audio round trip time. In this case it wasn’t significant enough in itself to have a noticeable impact as it still was well below the <200ms Microsoft recommends, but things like this, when combined with other factors can have an effect on the users experience of the call.

Dropped packages

Other factors like the total drop in packages sent & received for instance, that occurred right at the moment of the port change. As you can see in the picture below, the Audio packages being sent & received dropped to zero right when the change occurred, and then recuperated quickly.

The user may have experienced an interruption or glitch in the outbound and inbound audio stream, or a mid-call error when the Teams client re-established the connection.

Changes to the public facing ports can be harmless but can also cause problems in calls. When you notice mid-call changes happening often, and potentially causing problems, then look into the following:

Check with your firewall team to see if any of the above apply and whether changes should be made to improve the situation.

However…. It’s not always the firewall alone that can cause this.

Microsoft Teams calls are intricate and depend on many elements to fall into line all at the same time. Even small changes, like a public facing port changing mid-call, can cause issues that would be hard to detect without software that makes the full path of a call visible.

With the end-to-end insight into Microsoft calls that OfficeExpert TrueDEM offers, we can quickly help organizations identify what impacts their users’ Teams Call Experiences and if changes like the one above cause problems that need to be tackled. Contact us for a demo or to discuss the possibilities of a free trial with your own data.