[SIPForum-discussion] Early Media

Fri Apr 20 18:48:04 UTC 2007

UAC can expect different SDP in 183 and 200OK. a Non-reliable 183 is not the
final answer so if a 200OK comes with a different SDP, UAC has to honor it.
So for your case if the 183 carries the parametrs for early media for the
media servers, the 200OK will carry info the for "C" in your call example
and the originating UA has to change it.

Althought if the 183 was reliable ( using PRACK), the answer in 183
completes the offer answer but in that case 200OK can still carry a new SDP
which now would be taken as an Offer and not as an answer with origination
UA respong ACK with the answer,

Hope this helps.

M

  _____  

From: santosh patra [mailto:skp10_9559 at yahoo.co.in] 
Sent: Friday, April 20, 2007 4:12 AM
To: Siva M-Q16748; Robert Mansfield; discussion at sipforum.org
Subject: Re: [SIPForum-discussion] Early Media

Hello Siva

Please see my answers in line.

Regards
Santosh

----- Original Message ----
From: Siva M-Q16748 <sivam at motorola.com>
To: santosh patra <skp10_9559 at yahoo.co.in>; Robert Mansfield
<RJM at Redwoodtech.com>; discussion at sipforum.org
Sent: Friday, 20 April, 2007 1:14:55 PM
Subject: RE: [SIPForum-discussion] Early Media

Hi Santosh

This is the scenario

A calls ( throgh a B2BUA AS) B

B doesnot answer

Application Server sends INVITE to Media Server Application Server sends the
SDP info he got from Media Server to A in the 183 message A gets a Music
played by media Server 

[Santosh] Ok, fine...So this 183 Response has been generated by Media Server
and its one announcement server or you can say playing some music, Its only
one way means there is no response from UAC - "A" to this.

Now Application server forwards the call to C If C answers , A should get
the SDP info of C ( I thought it would be sent in 200 OK )

[Santosh] This time AS sends the same invite from A to C (Enabled CFNA
subscriber).....This time this invite-SDP is being offered to C and C will
respond with SDP-Answer to A...Obvious that there won't be same SDP for 183
and 200 Ok.

Siva M 

  _____  

From: santosh patra [mailto:skp10_9559 at yahoo.co.in] 
Sent: Friday, April 20, 2007 1:09 PM
To: Siva M-Q16748; Robert Mansfield; discussion at sipforum.org
Subject: Re: [SIPForum-discussion] Early Media

Hello Siva

As far as I understand, Early media one such type of featuer or functionaly
of UA/AS/gateway. Early Media means There will some ringtone played by
Gateway or local ringtone generated by UAC followed by Alert-Info
Header..Before 200 OK/ Final response.and I don't know why you need 183
"Session Progress" responce for this early Media....And its used in SIP-ISUP
interworking cases ACM in SS7 message same to 183 "Session Progress"  in
SIP....May be I ma missing something here the usage of 183 Response...Please
let me know.

As far your question concerns, 183 is a 1xx Provisional response which
doesn't contain SDP part  and SDP part comes in Offer/Answer model which one
should be negotiated between two end points. And I believe that 183 response
is not being used by any Endpoint, rather it would be sent by stateful
proxy/Gateway/AS...I don't know in which case 183 session progress has SDP,
If you have any valid scenarion then just let me know.200 OK is considered
as part of Offer/Answer model which one should be sent by Callee his SDP
capabilities....

Please correct me If I am wrong.

Cheers
Santosh

----- Original Message ----
From: Siva M-Q16748 <sivam at motorola.com>
To: Robert Mansfield <RJM at Redwoodtech.com>; discussion at sipforum.org
Sent: Friday, 20 April, 2007 10:36:01 AM
Subject: Re: [SIPForum-discussion] Early Media

Hi 

Would anybody be able to point out any Logical Reason why a 183 and 200
should not have same SDP ??

May be some scenario in which it creates issues ..

I hope there should be a Logical reason why RFC says so ..

Siva M 

-----Original Message-----
From: Robert Mansfield [mailto:RJM at Redwoodtech.com] 
Sent: Thursday, April 19, 2007 2:55 PM
To: Siva M-Q16748
Subject: RE: [SIPForum-discussion] Early Media

Siva,

If the use of early media is in the 'Gateway' model then I believe the
SDP descriptor in the 183 and 200 will be the same.

The scenario you describe is more akin to the Application Server model
(both models described in RFC 3960).

"Application Server sends the SDP info he got from Media Server to A in
the
183 message A gets a Music played by media"-In this case the B2BUA AS
could make use of the 'early-session' extension tag in the
'Content-Disposition'
header. This allows for the establishment of an early session with a
descriptor that is different from the SDP returned in the 200 OK.

"Server Now Application server forwards the call to C If C answers , A
should get the SDP info of C ( I thought it would be sent in 200 OK )"
Ok so now A needs to talk to C. The SDP descriptor is different and
represents the normal session represented by the INVITE/200/ACK.

I only have experience of this RFC in terms of the GATEWAY model so what
I'm not staking my life on the accuracy of this explanation however I
would be interested in your thoughts from RFC 3960 Application Server
model.

Hope this helps,

Rob.

-----Original Message-----
From: Siva M-Q16748 [mailto:sivam at motorola.com]
Sent: 19 April 2007 09:56
To: Robert Mansfield; discussion at sipforum.org
Subject: RE: [SIPForum-discussion] Early Media

Hi

If the 183 and 200 OK should have same SDP . How does the following
scenario
work ?? 

A calls ( throgh a B2BUA AS) B
B doesnot answer
Application Server sends INVITE to Media Server
Application Server sends the SDP info he got from Media Server to A in
the
183 message A gets a Music played by media Server Now Application server
forwards the call to C If C answers , A should get the SDP info of C ( I
thought it would be sent in 200 OK )

If 200 OK sent to A should have the same SDP as that of 183 , How can A
and
C talk in this case ..

Thanks
Siva M 

-----Original Message-----
From: Robert Mansfield [mailto:RJM at Redwoodtech.com] 
Sent: Thursday, April 19, 2007 1:54 PM
To: Siva M-Q16748
Subject: RE: [SIPForum-discussion] Early Media

Siva,

I'm not 100% sure but my understanding is that the early media WILL
contain
the same SDP descriptor as the 200 OK. There is a 'early-session' header
(look at RFC 3959 and 3960 for some guidance) that is used in an
Application
Server model for early media. This allows for different SDP descriptors
during session establishment.

>From my experience with PSTN-SIP Gateways (Gateway model) the descriptor
will be the same.

Rob.

-----Original Message-----
From: Siva M-Q16748 [mailto:sivam at motorola.com]
Sent: 19 April 2007 06:49
To: discussion at sipforum.org
Subject: [SIPForum-discussion] Early Media

Hi

In case of Early Media for announcements

Can 183 and 200OK have different SDP info 

Thanks
Siva M 

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