[SIPForum-discussion] Difference between UPDATE and Re-INVITE

[Ranjith Kumar]

HI,

I could give you some over view from the RFC.


The Session Initiation Protocol (SIP) [1] defines the INVITE method

for the initiation and modification of sessions. However, this

method actually affects two important pieces of state. It impacts

the session (the media streams SIP sets up) and also the dialog (the

state that SIP itself defines). While this is reasonable in many

cases, there are important scenarios in which this coupling causes

complications.

The primary difficulty is when aspects of the session need to be

modified before the initial INVITE has been answered. An example of

this situation is "early media", a condition where the session is

established, for the purpose of conveying progress of the call, but

before the INVITE itself is accepted. It is important that either

caller or callee be able to modify the characteristics of that

session (putting the early media on hold, for example), before the

call is answered. However, a re-INVITE cannot be used for this

purpose, because the re-INVITE has an impact on the state of the

dialog, in addition to the session.

As a result, a solution is needed that allows the caller or callee to

provide updated session information before a final response to the

initial INVITE request is generated. The UPDATE method, defined

here, fulfills that need. It can be sent by a UA within a dialog

(early or confirmed) to update session parameters without impacting

the dialog state itself.
Hope it helps.

Regards,
Randy

On Tue, Sep 29, 2009 at 10:45 PM, SIP SIP <yansb43 at gmail.com> wrote:

> Hi All,
>
> Hope all of you are doing fine.
>
> Here I am with a age old query.
>
> Difference between UPDATE and Re-INVITE.
>
> One basic difference is-----
>
> Re-INVITE cant be sent before session is established.But UPDATE can be sent
> always.
>
> Is there any other major difference?????
>
> Thanks
>
>
>
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