-SIP- Early Offer , Delayed Offer , Eraly Media

Below is The basic Sip messages

In Early offer, SIP Send SDP in the invite , the other part will send the SDP in the ringing message  the other part will send the SDP in the 200 message

In delay offer , SIP send the SDP in the ok200 ,the answer will be send back in the ACK message

SDP: Session Description Protocol , this protocol will negotiate codecs , type , encryption ….

Why using Early offer : SIP provider use the early offer to force using their codecs

Don’t  confuse with Early Media

Early Media is the Media that will be sent before completely establishing the SIP session

In the figure above the ring-back tone is generated  on the remote side at step 4

In the figure above the ring-back is generated locally at step 2

To resume early offer and early media are two different things , we can have early media and early offer at the same time ,or to have one but not the second

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3 Responses to -SIP- Early Offer , Delayed Offer , Eraly Media

  1. There is definately a lot to know about this issue.
    I really like all of the points you have made.

  2. Anonymous says:

    You mentioned that “…the other part will send the SDP in the ringing message”. That is not true. Called party will send its SDP in 200 OK response.

    • True , although we can still send the SDP in 180 message but this will apply for early media , in fact we can send SDP even for delayed media as long as we send the same sdp in 200 message or ACK message

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