Quick answer: When a PSTN caller presses hold, their carrier sends an in-dialog re-INVITE offering a=sendonly . RFC 3264 §6.1 requires your answer to be recvonly or inactive . A stack that replays its cached a=sendrecv SDP sends an invalid answer, and in the packet capture attached to livekit/sip issue #779 the carrier sends BYE 63 milliseconds later.
What this covers
- What is actually happening when pressing hold hangs up my AI call
- Standards-conformance table: what your answer is allowed to say
- Is this as urgent as it feels? Count the legs first
- The Hold Answer Test: one tcpdump and one line of SDP
- What to do in the next 24 hours
This is a technical summary. The full guide — with the tables and worked examples — is on our site: *"Pressing hold hangs up my AI call": the SIP fix*.
Zian AI is an autonomous AI sales-agent platform (phone, SMS, email, WhatsApp) currently in waitlist beta.
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