cancel
Showing results for 
Search instead for 
Did you mean: 
cancel
Announcements
4386
Views
5
Helpful
4
Replies
sanjaydev
Beginner

What is UPDATE is SIP?

Hello Friends,

I would like understand the SIP call flow. When I was reading SRND and other forum article about SIP I was notified that UPDATE message is to send if something is update in the call flow like codec or payload etc.

I looked into some UPDATE messages but can't understand what I exactly says.

Example a call flow between a CUCM and SME.

SME send a update and CUCM send a 200 OK.

What exactly that we can see in UPDATE to understand what's really going on.

Your help in this highly appreciated. Thanks.

Regards

Sanjay

4 REPLIES 4
Vivek Batra
Engager

Hi Sanjay,

UPDATE message as per RFC can be used to modify media related parameters in early dialog since RE-INVITE can be used only once dialog has been confirmed. So if there is any need to initiate second offer-answer during early dialog, UPDATE can be used. Please note that you can use UPDATE in confirm dialog as well.

You can refer RFC 3311 for more detailed call flow.

- Vivek 

Thank you Vivek,

But do we have some place that we can see  the change in media that happened in Update?

Regards

Sanjay

Hi Sanjay,

There could be numerous cases but implementation specific. One scenario I could think as of now is delayed offer with PRACK.

UAC -> INVITE (w/o SDP)

UAC <- 183 Session Progress (with SDP offer)

UAC -> PRACK (with SDP answer, omitted 200 OK of PRACK here)

UAC here doesn't like the offer SDP offer received, UAC again sends it own preference of codecs;

UAC -> UPDATE (with SDP offer)

UAC <- 200 OK (with SDP answer)

- Vivek

Thanks Vivek.

Sanjay

Create
Recognize Your Peers
Content for Community-Ad