SIP over TLS toward the carrier

Signaling for Four ways to reach the PSTN. Teams keeps the dialog. A 488 is codecs, not a greeting.

Sources and go deeper

Same checked list as T05-R01-four-ways-to-reach-the-pstn.html.

PSTN connectivity options — Microsoft Learn — last checked 2026-10.
Plan Direct Routing — Microsoft Learn — last checked 2026-10.
RFC 3261 — RFC — last checked 2026-10.
Public switched telephone network — Wikipedia — last checked 2026-10. Wikipedia fallback for background. Confirm the vendor page before you change a tenant
Session Initiation Protocol — Wikipedia — last checked 2026-10. Wikipedia fallback for background. Confirm the vendor page before you change a tenant
Microsoft Teams blog index — Community — last checked 2026-10. Community index for the Microsoft Teams blog. This is the index, not a claim that a post discusses this room

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