Callee rejects a 1:1 call

Status: draft
Spec version: 0.1.0

Summary

The sequence when the callee actively declines an incoming 1:1 call instead of answering. The caller's is routed to the callee, which (without ever accepting) sends a carrying the call-id/call-creator and a reason (e.g. declined). The server acks and routes the rejection back to the caller, whose UI shows the call as declined, and propagates a "reject_elsewhere" terminate to the callee's other linked devices so they stop ringing. No media is ever established. Step ordering and reason tokens are a working model and hedged.

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 with per-device <enc> call key and transport candidates.
  server->>callee: routed <call><offer> delivered to callee [probable]
  Note over server,callee: Callee device(s) begin ringing.
  callee->>server: <reject reason='declined'> call-id call-creator [probable]
  Note over callee,server: Callee user declines no <accept> is ever sent so no SRTP keys are derived.
  server->>callee: <ack class='call'> for the reject [speculative]
  Note over server,callee: Server acknowledges the rejection back to the rejecting device.
  server->>caller: routed <reject> delivered to caller [probable]
  Note over server,caller: Caller UI shows the call as declined.
  server->>callee: <terminate reason='reject_elsewhere'> to callee's other devices [speculative]
  Note over server,callee: Other linked callee devices stop ringing once one device has rejected.

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 with per-device call key and transport candidates.
2	server	callee	routed delivered to callee	call-offer	probable	Callee device(s) begin ringing.
3	callee	server	call-id call-creator	call-reject	probable	Callee user declines; no is ever sent so no SRTP keys are derived.
4	server	callee	for the reject	call-ack	speculative	Server acknowledges the rejection back to the rejecting device.
5	server	caller	routed delivered to caller	call-reject	probable	Caller UI shows the call as declined.
6	server	callee	to callee's other devices	call-terminate	speculative	Other linked callee devices stop ringing once one device has rejected.

Open questions

• Is the decline carried by a dedicated stanza, or a ?
• Does the reject reason token match a value in the terminate-reasons enum, or a separate set?
• Is the "reject_elsewhere" propagation server-originated or peer-originated?

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