Learn what a SIP Delayed (late) Offer means, how it differs from an Early offer, its impacts SIP Call Setup and integration with the Intelligent Voice Platform.
During the SIP Call Setup process, a SIP INVITE message is sent to request establishment of the call which contains key information such as:
- Called Number - What is the number being called?
- Calling Number - What is the Caller ID / Calling Number who is making the call?
- Media "Offer" - What CODECs are supported, where to send media and encryption details
The Media "Offer" is part of the SIP Offer / Answer model used during call setup to negotiation of what each end of the call can support from a voice, video and DTMF point of view which is exchanged within SIP messages using the Session Description Protocol (SDP).
In most cases for SIP based Telephony / Voice Over IP the initial SIP INVITE message will include an "Offer" in the form of SDP, which is known as an "Early Offer" and provides all the details required to establish the call from voice or video point of view straight away with minimal delay.
SIP "Delayed Offer" (sometimes called Late Offer) refers to a situation where an outgoing SIP Call is initiated via a SIP INVITE message, but it does not include any SDP or other media details which are negotiated later in the call rather than being provided "up front" to minimize call setup times.
SecureCo's Intelligent Voice Platform does not support "Delayed" or "Late Offers" and only supports "Early Offer" which requires all initial INVITES to include SDP.
Where a customer's equipment only supports Delayed Offer, SecureCo has found in all cases so far that there are interworking configuration options available on their SBC's or PBX that ensure that all initial INVITES sent to the IVP will contain SDP.