Example analysis
What the result looks like — no sign-up, on a real case.
Diagnosis result
PCAP-2026-0042 · Callee (B-party)
Summary: The called party rejects the call with 486 Busy Here — the destination is busy. No network or routing fault.
Finding
The capture contains exactly one call. After the INVITE and a 100 Trying, the called side responds directly with 486 Busy Here. There is no 180 Ringing and no RTP stream — the call never connects and never even rings.
Cause
486 Busy Here is sent by the called side and means "busy". Because it arrives immediately, without ringing, the B-party is either genuinely busy (with no call waiting), deliberately rejecting (DND / "busy on busy"), or a channel/line limit on the trunk or SBC has been reached.
Recommendation
- Check the destination for "Do not disturb" (DND) or a "forward on busy" rule — the most common cause.
- Check the channel/license limit on the trunk/SBC if it is only "busy" at peak times.
- Verify the "simultaneous calls" setting of the extension.
The evidence points clearly to the B-side — no action is needed in the network.
Customer note
The call was rejected by the far end as busy (SIP 486 Busy Here). This points to a busy line, an active "forward on busy" / "do not disturb" setting, or a reached line limit — not a network fault. Please check at the destination whether "do not disturb"/call waiting is set and how many simultaneous calls are allowed.
SIP Call Flow
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