[SIPForum-discussion] Early Media

Fri Apr 20 08:11:37 UTC 2007

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

DIV {
MARGIN:0px;}

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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