Asterisk

Inbound or outbound DTMF digits are ignored or duplicated by IVR systems and remote endpoints due to dynamic payload type mismatches, missing SDP telephone-event negotiation, or dual-transmission (RFC 2833 combined with in-band audio tones) across SIP trunks and Session Border Controllers (SBCs).

Inbound or outbound SIP calls fail immediately during session setup with a '488 Not Acceptable Here' status code due to incompatible SDP media attributes, codec list mismatch, or mismatched ptime settings between the calling and called endpoints.

Outbound INVITE requests sent to a SIP carrier trunk are rejected with a '403 Forbidden' response during or immediately following digest authentication challenge handling.