03-21-2019 09:24 AM
So early offer is when the calling party shares the media codec and rtp ip/ports in the Invite message, correct ? Whereas delayed offer is where the media content is shared after the 200 ok message, is that correct?
Can someone please explain early media and delayed media? Also what are the advantages/disadvantages of early/delayed offer/media.
03-22-2019 03:53 PM
hi,
in simple term, the media that sent before the actual connect is called early media and vice versa. Early and late media actually have nothing to do with early and late offer.
in SIP and VOIP you will see signals like 183 session and PRACK when there is early media.
for more detail refer :
https://tools.ietf.org/html/rfc3960
https://www.ietf.org/rfc/rfc3262.txt
advantage can be : to play ringback tone, IVR tones etc.
thanks
03-23-2019 11:43 PM
03-25-2019 09:53 PM - edited 03-25-2019 09:53 PM
that post is famous @HARIS_HUSSAIN
03-25-2019 05:04 AM
First, SIP has three way handshake model. INVITE, 200OKAY, ACK.
Second, SDP(IP, Port, Codec) payload can be in any of the three SIP messages.
Third, SIP is based on offer/Answer model. You offer SDP and if capabilities are common you will get an Answer
Early Offer
A-----------------B
---Invite(SDP)--->
<---200Okay(SDP)---
~~~~~~~rtp~~~~~~~~~
---ACK--->
Delayed offer
A-----------------B
---Invite--->
<---200Okay(SDP)---
---ACK(SDP)--->
~~~~~~~rtp~~~~~~~~~
Early Media (if you are able to complete xchange(offer/answer) of SDP before the 200okay of INVITE its early media)
Type1:
A-----------------B
---Invite--->
<---183(SDP)---
---PRACK(SDP)--->
~~~~~~~rtp~~~~~~~~~
<---200Okay---
---ACK--->
Type 2:
---Invite(SDP)--->
<---183(SDP)---
~~~~~~~rtp~~~~~~~~~
---PRACK--->
<---200Okay---
<---200Okay---
---ACK--->
Refer to RFC 6337 for more information:
Regards,
Adarsh Chauhan.
Please mark helpful or correct
03-25-2019 11:39 AM
03-25-2019 09:50 PM
To keep it simple I would divert you as this has been already answered on this post
However don't be surprised if you see 180 with SDP.
vendors interpret rfc in different ways as they leverage the keywords may, should, etc.
However if in rfc something is mentioned as must the vendor device should strictly adhere to it.
Regards,
Adarsh Chauhan
Please mark helpful or correct
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