[SIPForum-discussion] Is SDP body is required for Refresh Invites.........?

[Sriram Subramanian]

Hi,
       Its actually a good question ?? but not mentioned anywhere in the
RFC's detailing the behaviour ,But i have seen a case in my test bed which i
would like to share .

I have an IP phone CISCO 7960 series that actually differentiates between
reinvite and Session refresh invite based on the "Session-Version"
incremental value.The SDP body (Codecs,attribute states) ,even if u change
in a Session Refresh Invite it is not taking it into account it first checks
the 'o' lines in the SDP to see if it is incremented and then if it is not
incremented it simply ignores the other lines .This was confirmed in my
testbed when a call hold scenario was tried without incrementing the Session
Version value in the 'o' line and the ip phone did not identify it as a Hold
scenario.

Now coming to your point of mainting  the SDP body in a refresh invite .As
long as you maintain the mandatory headers declared in both RFC 2327 (m line
is mandatory as per this RFC) as well as RFC 4566 in the SDP body even if u
miss the optional headers it should not create a problem mostly.

Regards,
Sriram





On Wed, Nov 25, 2009 at 12:05 PM, Govindraj.B.H @ Gkk <
govindraj_h at yahoo.co.in> wrote:

>   Hi,
>       As per my knowledge, the main intention of Session Refresh Requests
> is to inform the intermidiate elements about the session aliveness. Which
> can be served by normal Invite. Why do we need to send the session body
> along with all the session refresh Invite requests there by increasing the
> traffic density.
>
>     There is a parameter which differentiate the "Re-Invites" with the
> "session refresh Invite" request i.e *"Session-Version". ( SV increments
> for each Re-Invite but remains constant for all the session refresh requests
> ). *
> **
>    Is there any other reason behind sending the body in Session Refresh
> Invites.........?
>
>   [ If it is the only reason ( Session-Version ) to differentiate the
> Re-invites with the Refresh Invites, then there is no point in sending the
> Body params along with the session refresh Invites. Still we can
> differentiate both the requests. Invite with "Content-Length = 0" is a
> Refresh Invite and "C-T = Non-zero" is an Re-Invite. So with
> this implementation we can reduce the traffic overhead. ]
>
> All, plz provide me your inputs/suggestions for the above discussion.
>
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