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Your voice platform receives WhatsApp calls as ordinary SIP calls on a trunk you provide. Any standards-compliant SIP platform works: an IVR, a contact-centre platform, a SIP server or a voice bot.

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What your platform provides

Allow the OneXtel gateway to reach your platform for both signalling and audio. OneXtel gives you the gateway addresses during onboarding. Keep them allowed in every firewall between the internet and your platform.

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What your platform receives

Each call arrives as a SIP INVITE with an SDP offer.

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What your platform must do

1

Answer the call

Reply with 180 Ringing if you like, then 200 OK with an SDP answer that picks one of your accepted codecs.
2

Send audio first

Start sending audio as soon as you answer: a greeting, music, or silence. WhatsApp waits for the business side to send first. A platform that only listens produces a silent call.
3

Send and receive on the addresses in the SDP

Use the audio address and port in the gateway’s SDP. Send your audio from the same address and port you advertise.
4

End the call with BYE

Either side may send BYE. The gateway closes both legs.

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Routing options

Choose how the gateway addresses your trunk. This is set per trunk.
Some platforms, such as voice AI agent platforms, match the call to a number or agent you imported there by an identifier. Choose A fixed SIP user and enter the identifier exactly as you imported it, including capital letters and any leading plus sign. The gateway puts it in both the request line and the To header. If the call is answered with 404, the identifier usually does not match. See Troubleshooting.

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Failover and fallback

You can attach more than one trunk to a number, for example your main platform, then a backup agent or a human queue. The gateway tries them in priority order and moves to the next trunk when:
  • the trunk gives no response within the failover time,
  • the trunk answers with a server error (5xx),
  • the trunk rings but does not answer within its ring limit, or
  • the trunk rejects the call as busy, unavailable or declined (480, 486, 600 or 603), if you turned on try the next trunk for that trunk.
Without that last setting, a busy or decline is passed back to the caller as it is. A trunk that has reached its call limit is skipped. If there is no further trunk, the call fails and the caller hears it.
The ring limit starts when your platform replies Ringing. Until then, the failover time applies. When the limit passes, the gateway cancels the call to that trunk and sends it to the next one, so your platform sees a normal CANCEL.
Use a ring limit together with try the next trunk on a platform that can be briefly unavailable, such as a voice AI agent that is at its concurrency limit. The caller then reaches a working destination instead of waiting for the call to fail. Keep the ring limit short. Ask your account team to attach the backup trunk and set the limits.

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During the call

  • Re-INVITE (for example hold and resume) is passed through.
  • Transfers should be done inside your platform. The gateway does not transfer calls on to other WhatsApp numbers.
  • Keypad tones (DTMF) arrive as standard RFC 4733 telephone-events. See Protocols and media.