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Collaboration, Voice & AV · Advanced

Delayed Offer (DO)

A SIP call flow in which the INVITE has no SDP, so the callee makes the offer in its 200 OK and the caller answers in the ACK.

Definition

Delayed offer lets the caller learn the far end's capabilities before committing media details and avoids needing media resources early. It is the CUCM SIP trunk default. Its drawback is that some providers require early offer and that early media is harder to support.

Example

CUCM sends an INVITE without a body; CUBE responds 200 OK with an SDP offer, and CUCM sends ACK with the SDP answer.

Exam tip

Remember: delayed offer means offer in 200 OK, answer in ACK.

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