SkypeExchange4U
Teams Direct Routing, SBC, and hybrid identity guides
Practical Microsoft Teams voice and Entra ID notes from real deployments. Call flow, SBC setup, and troubleshooting. No fluff.
SkypeExchange4U
Teams Direct Routing, SBC, and hybrid identity guides
Practical Microsoft Teams voice and Entra ID notes from real deployments. Call flow, SBC setup, and troubleshooting. No fluff.
When Microsoft Teams Direct Routing throws a SIP 403 Forbidden, call setup is dead on arrival. Unlike a 503 error—which triggers route failover—a 403 is a hard rejection. The server is telling you: “I received your INVITE, I understood it, and I refuse to process it.” In production enterprise voice deployments, 403 errors split into…
Short answer: A SIP 503 Service Unavailable error in Microsoft Teams Direct Routing indicates that a component in the call path—either the Microsoft SIP proxy, your Session Border Controller (SBC), or the upstream PSTN carrier—is temporarily unable to process the call. The most common causes are failed SIP OPTIONS heartbeats, TLS certificate issues, carrier trunk…