Controlling Your Own Telephony Integration Between Teams and PSTNs

As the global pandemic took hold over the past 18-months many organizations moved to a hybrid work model, which required employees to make VoIP calls and participate in online meetings from any location. This became a vital service offering from IT groups to maintain productivity and ensure continued business success. And as it happens, one of the best things about Microsoft Teams is its flexible voice communications capabilities. As more enterprise organizations have standardized on Teams as their everyday telephony system, they have placed more pressure on IT operations to maintain an acceptable user experience. The same IT groups that support e-mail and collaboration tools, now must support telecom as well. And the integration between Microsoft Teams and the public switched telephone network (PSTN) for a broadly distributed organization is extremely complex.

As reported in a previous blog, the most popular integration method between Teams and PSTN is to configure Direct Routing through a Session Border Controller (SBC) gateway. Metrigy’s recently published study on Workplace Collaboration: 2021-22 reviewed 476 organizations and found that more than 70% of those adopting Microsoft Teams Phone System are using Direct Routing to connect Teams to the PSTN backbone. And as organizations have abandoned their old PBX systems on-premises, they rely on rented links (SIP Trunk Lines) from telecom carriers to access the PSTN backbone. When an incoming call is received, the SBC gateway mediates a session from the carrier and transforms it to match the flavor and requirements of Microsoft Teams. It is then passed through to the Microsoft Teams environment and on to the intended user. It works the same way in reverse. An outgoing call is routed through the company’s Teams network to the SBC gateway and then to the recipient via the SIP trunk line provided by the carrier. In this way, Direct Routing offers organizations a great deal of flexibility when it comes to their voice infrastructure, enabling them to adopt a “bring your own carrier” (BYOC) approach for each geographic location.  So, at the other end of that PSTN linkage are telecom service providers around the world that rent out SIP trunk lines as the connection points to the SBC gateways. 

And therein lies the obvious conundrum for a bottleneck and troubleshooting nightmare.  There is only so much call traffic that can make it through an SBC gateway and the associated SIP trunks at any given time.

Rightsizing that throughput for optimal call quality during peak business hours is tricky, and the responsibility falls squarely on the shoulders of the IT group supporting Teams enterprise voice.

Full-Visibility for Rightsizing PSTN Call Integration

To maintain the best Teams call quality for an enterprise organization it is imperative that IT operations groups have complete end-to-end visibility into the different segments that can cause bottlenecks which negatively impact performance. This is especially true for SBC gateways and the associated SIP trunk lines that pass call traffic back and forth between Teams users and external phone networks. Closely monitoring this throughput during peak business hours is essential to ensure those communication pathways don’t become swamped.

Realize that the telecom carriers are likely to blame anyone but themselves for reported call quality issues. Those SIP trunk providers may give some visibility into their endpoints and ability to handle traffic. But usually, they will prevent a customer from seeing too much, as they never want to expose that they have problems when dealing with heavy loads. The best pieces of information you can track on their performance is to flag the specific times when you have problems with them, gather a listing of the SIP error codes, and log how many calls your SBC was processing during that time span.

The other big area to monitor closely is the concurrent network traffic for all calls going into and out of the SBCs. This is typically the source of call quality problems, as many issues can exist in the network elements involved between the SBCs.

  • Links can get overloaded during peak traffic times and drop packets
  • Gateway devices can get overloaded and drop packets
  • Load balancing and multiple route-paths can cause out-of-order packets
  • Route patterns can change, causing latency and jitter swings

Then it comes down to the daunting tasks of researching and troubleshooting these issues, especially for IT operations teams that are new to supporting telecom traffic. And remember that log files get wiped after a certain amount of time, which makes background investigations nearly impossible. Having all that information at your fingertips with the detailed telemetry data for each call that occurred over the past month, or 6-months, can be a huge time savings.

Figure 1: Direct Routing Call Analysis

Figure 2: Concurrent SIP Trunk Line Usage by Country (Success / Failures)

Single-Pane-of-Glass for Monitoring and Troubleshooting

Being able to monitor and track the entire journey for the Direct Routing of PSTN voice traffic requires visibility from the user endpoint perspective and at the gateways. There are many factors at play during the end-to-end journey, and unless you are measuring throughput from each user endpoint and SBC, you just don’t know what the cause for the bottlenecks may be. An SBC may become overloaded during peak business hours. Or a SIP trunk line might get maxed out and start dropping calls.

Only when you have an integrated monitoring toolset that links the client-side information and endpoint device metrics to the performance analytics of the network segments and SBC gateways do you have a full understanding of performance for Teams enterprise voice. And having all that information inside a single interface makes it much easier for IT support teams to do analysis and troubleshooting quickly.

OfficeExpert EPM gathers all that telemetry data, combines it with the Teams call performance classifications from Microsoft CQD, and organizes it into actionable intelligence using dashboards, graphical reports, and drill-down data views. By leveraging real-time and historic data about Teams call quality performance at global, local, and individual levels an organization can pinpoint, resolve, and often prevent disruptions to communications that affect productivity and stall business communications. The main areas where OfficeExpert EPM assists IT support and operations teams with their Direct Routing for PSTN integration include the following:

  • Identify SBCs that are overloaded with call traffic during peak usage times
  • Spotlight overloaded SIP trunk lines at gateways
  • Optimize routing and load balancing for environments with multiple SBCs
  • Ensure compliance with Toll Bypass regulations

Find Out More…

If you would like to take a more proactive approach to monitoring and troubleshooting your Teams enterprise voice call quality levels, right size your SBC gateways, and optimize your direct routing configurations, then you need to see the complete picture.  To learn more about our OfficeExpert EPM data analytics solution and how it can help you revamp your Teams enterprise voice deployment, please visit our overview page online, or sign-up for a trial at