[SIPForum-discussion] What's the info contained in the SDP?

[Mike Jiang]

Thanks for all the answers. It makes sense from all the explanations.
For special case I ran into, the service provider we used always sent their 
RTP server's listening IP/Port as well as the audio codecs in the SDP as the
body of the SIP msgs (either in the 183, the 180 (both optional), or the
200(a must)). We wanted them to send the SDP info as soon as possible, for
example, having the SDP in the 183 msg, so we have enough time to initialize
and make the voice engine ready for voice communication.

The only issue confusing me is that the service provider remained saying
that the IP/port in the SDP would be sent only after receiving the feedback
from the callee's data carrier. I guessed it was a pure business
consideration rather than a tech issue, then.

Thanks,

Mike J.



-----Original Message-----
From: Clint Perry [mailto:cperry15 at gmail.com] 
Sent: Tuesday, July 14, 2009 9:48 PM
To: devibalas sdevibala
Cc: Mike Jiang; discussion at sipforum.org
Subject: Re: [SIPForum-discussion] What's the info contained in the SDP?

Technically 183 can carry SDP as well...

SDP is the Audio Setup for the device sending the SDP....

That defines the ports and IPaddress for the SIP "Speaker" to send the
audio.

A will send to B its codecs, IP and Ports that he is "going" to use
for that session


B does the same


-CP

On Tue, Jul 14, 2009 at 9:01 AM, devibalas
sdevibala<msg4devibala at gmail.com> wrote:
>
> Hi Mike,
>    As far as ur call is concerned the SDP info can either be carried in
180
> ringing or in 200OK. The SIP server will send back the SDP info of the
> called party(B) to the calling party(A). The server either has this info
> stored(Purely IP) or if the called party  is connected to a CODEC/GW then
it
> uses MEGACO protocol to create a session get the SDP info & passes it on
to
> the calling Side.
>
> Rgds,
> DBS
>
>
> On Mon, Jul 13, 2009 at 9:43 PM, Mike Jiang
<mike.jiang at andersontaylor.com>
> wrote:
>>
>>  Hi, All
>>
>>       I have a quick question: when I make a call from a SIP phone, the
>> SIP server sends 183 Session Process, 180 Ringing, and 200 OK msgs
>> sequentially back
>>
>>  to the phone. Usually at least one of three above has the SDP as the
>> body. The SDP contains the info about the IP, port, and audio codecs of
the
>> target. My question is: is the IP/port that of the SIP Server or the
>> callee’s phone? The reason why I ask this is: the SIP phone only talks
with
>> the SIP server directly, then the SIP server manages to relay voice
packets
>> to the callee. As for how the SIP server routes the call to the callee,
>> that’s not the business the SIP phone cares.  So I think the IP/Port in
SDP
>> is that of the SIP server rather than the callee’s phone. The SIP server
>> provider told me it’s the callee’s. I got confused.
>>
>>
>>
>>       Thanks for any input,
>>
>>
>>
>>       Mike J.
>>
>>
>>
>>
>>
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database 3832 (20090206) __________

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__________ Information from ESET NOD32 Antivirus, version of virus signature
database 3832 (20090206) __________

The message was checked by ESET NOD32 Antivirus.

http://www.eset.com