Consider a scenario where there is no direct path between the two peers or between a peer and a conference server and you are joining a multi-party call or meeting. The HdxRtcEngine.exe uses a Microsoft Teams transport relay server in Microsoft 365 to reach the other peer or the media processor, where meetings are hosted. Your client machine must have access to three Microsoft 365 subnet IP address ranges and four UDP ports (or TCP/TLS 443 as fallback if UDP is blocked). For more information, see the Architecture diagram in the Call setup and Office 365 URLs and IP address ranges ID 11.