For customers that need to manage their own on-net voice quality for Microsoft Teams, Direct Routing offers an option for Local Media Optimisation (LMO). The overarching principle is that by determining an end user’s location, when on the corporate network, the system will allow the voice path to be negotiated between the Teams client and the internal IP address of one of the customer’s (certified) SBCs. Hence, keeping the media within the customer’s domain, which allows QoS to be applied and honoured for PSTN calls.
Users who are roaming outside of the Enterprise network will establish a voice path with the public IP address of one of the corporate SBCs. Or via a Transport Relay Point if the customer’s security policy blocks direct inbound access to the SBCs.
Behind the scenes the Microsoft Teams platform uses a predefined virtual topology and “trusted IP addresses” to identify on a call by call basis whether the end user is either inside or outside of the corporate network. Depending on the location SIP X-MS headers will be used to tell the SBC where the Teams client is located.
This is an advanced configuration so I created the video demonstration below to help me explain the basic concepts. If this is a new area for you. I hope it helps!
For additional information, please check out the Microsoft documentation. After taking some time to review my video it should make for easier reading.