Missed 1:1 call (no answer, ring timeout)

Status: draft
Spec version: 0.1.0

Summary

The sequence when a 1:1 call rings unanswered until the ring timeout elapses, producing a missed call. The caller's is routed to the callee, which rings (optional ) but the user never answers. When the timeout is reached, a with reason timeout ends the call: the caller's side logs an outgoing missed/unanswered call and the callee's side logs an incoming missed call. No occurs and no media is set up. Whether the timeout fires caller-side, callee-side, or server-side, and which party emits the terminate, is uncertain and noted in open questions.

Sequence

sequenceDiagram
  autonumber
  participant caller as Caller (initiating device)
  participant server as WhatsApp server
  participant callee as Callee device
  caller->>server: <call><offer> placed [probable]
  Note over caller,server: Standard offer per-device <enc> call key delivered but never used.
  server->>caller: <ack class='call'> for the offer [probable]
  Note over server,caller: Confirms the offer was routed.
  server->>callee: routed <call><offer> delivered to callee [probable]
  Note over server,callee: Callee device(s) ring.
  callee->>caller: <preaccept> (ringing), but user never answers [speculative]
  Note over callee,caller: Optional ringing indication no <accept> follows.
  caller->>callee: <terminate reason='timeout'> after ring timeout [probable]
  Note over caller,callee: The unanswered call is torn down with reason timeout, surfacing as a missed call on the callee and an unanswered/cancelled call on the caller. Which side originates the terminate is uncertain.
  callee->>server: <ack class='call'> for the terminate [speculative]
  Note over callee,server: Acknowledges the teardown.

Participants

• Caller (initiating device) (caller)
• WhatsApp server (server)
• Callee device (callee)

Steps

#	From	To	Message	Stanza	Confidence	Note
1	caller	server	placed	call-offer	probable	Standard offer; per-device call key delivered but never used.
2	server	caller	for the offer	call-ack	probable	Confirms the offer was routed.
3	server	callee	routed delivered to callee	call-offer	probable	Callee device(s) ring.
4	callee	caller	(ringing), but user never answers	call-preaccept	speculative	Optional ringing indication; no follows.
5	caller	callee	after ring timeout	call-terminate	probable	The unanswered call is torn down with reason timeout, surfacing as a missed call on the callee and an unanswered/cancelled call on the caller. Which side originates the terminate is uncertain.
6	callee	server	for the terminate	call-ack	speculative	Acknowledges the teardown.

Open questions

• Does the ring timeout fire on the caller, the callee, or the server?
• Which party originates the on timeout?
• Is a caller-initiated cancel (caller gives up early) a distinct reason from timeout?
• Are other linked callee devices terminated with timeout or an "elsewhere" variant?

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