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Call Pre-Accept

Tag: <call>
Category: signaling
Status: draft
Spec version: 0.1.0
Direction: outgoing, incoming

Summary

An early-acknowledgement stanza emitted by a callee device after it has received and decrypted the offer but before the user has answered. The node wraps a child echoing the call-id and call-creator. It signals "your offer reached me and I am now ringing", letting the caller show an accurate ringing state and optionally begin transport warm-up. It is not a commitment to accept the call. From the ringing device this is outgoing; from the caller it is incoming. Details below are a working model, not yet confirmed by a real capture.

Attributes

Name Type Required Confidence Description Provenance
from jid yes probable JID of the ringing callee device emitting the pre-accept.
observed: B.0:7@s.whatsapp.net		 techniques: websocket-capture; sources: none
to jid yes probable JID of the caller the pre-accept is routed to.
observed: A@s.whatsapp.net		 techniques: websocket-capture; sources: none
id string yes probable Stanza id used to correlate the server for this pre-accept.
observed: 3C4D5E6F70		 techniques: websocket-capture; sources: none

Children

<preaccept>

occurrence: 1 - confidence: probable

Container marking the call as received-and-ringing. Echoes the session identifiers. It may optionally carry early transport candidates so the relay handshake can begin while the phone rings, but it carries no acceptance.

Attributes

Name Type Required Confidence Description Provenance
call-id string yes probable The logical call session id, copied verbatim from the offer.
observed: CALLID-0001-synthetic		 techniques: websocket-capture, baileys-instrumentation; sources: none
call-creator jid yes probable JID of the call creator (the caller), copied from the offer.
observed: A@s.whatsapp.net		 techniques: websocket-capture; sources: none

<destination>

occurrence: 0..1 - confidence: speculative

Optional early transport candidates, allowing relay warm-up before the user answers. Whether pre-accept carries these or they wait for is unconfirmed.

<te>

occurrence: 0..n - confidence: speculative

A transport endpoint candidate advertised early by the ringing device.

Attributes

Name Type Required Confidence Description Provenance
ip string no speculative Candidate IP address (synthetic example only).
observed: 203.0.113.20		 techniques: websocket-capture; sources: none
port int no speculative Candidate UDP port for media.
observed: 3478		 techniques: websocket-capture; sources: none

Examples

Illustrative pre-accept / ringing (synthetic)

Synthetic and sanitized, not a real capture. Whether carries early candidates is an open question; a bare form is also plausible.

<call from="B.0:7@s.whatsapp.net" to="A@s.whatsapp.net" id="3C4D5E6F70">
  <preaccept call-id="CALLID-0001-synthetic" call-creator="A@s.whatsapp.net"/>
</call>

Notes

Pre-accept is the protocol's analogue of an SIP 180 Ringing: it confirms delivery and that the device is alerting the user, distinct from the actual . Not every device or call necessarily emits it, so the caller must not block on it.

Open questions

  • Is always emitted, or only under certain client versions / network conditions?
  • Does pre-accept carry early transport candidates, or is transport deferred to ?
  • In multi-device, do all ringing devices send pre-accept, and how does the caller aggregate them?

References

Back to stanza catalog - Spec overview