Early and delayed offer, early and delayed media.

[sourajit01]

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.

[tgaur]

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

[HARIS_HUSSAIN]

Below will help

https://andrewjprokop.wordpress.com/2014/04/18/sip-media-management-early-media-vs-late-media/

*** Please rate helpful post; Mark "Accept as a Solution" if applicable

Thanks,
Haris

[Dennis Mink]

that post is famous @HARIS_HUSSAIN 

[Adarsh_Chauhan]

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.

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[sourajit01]

Thanks Adarsh. Please help me understand the difference between 180 ringing and 183 ringing messages. I see 183 ringing message coming into picture for early media only, is that true?

[Adarsh_Chauhan]

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