Subject: [MMUSIC] Question on the IP address/port indicated in an SDP offer

From: "Javier Gonzalez Gallego" <[email-masked]>
Date: Fri, 15 Jul 2005 16:54:09 +0100

Hello,
I have found 2 sentences that seems contradictories in RFC 2337 and in
RFC 3264 regarding the use of the IP address and port in the SDP offer. 
Is this really a contradiction or not?

Based on RFC 3264, the IP address/source indicated by the offerer are
the ones to be used to "receive" media. Especifically it says later "For
recvonly and sendrecv streams, the port number and address in the offer
indicate where the offerer would like **to receive** the media stream.
For sendonly RTP streams, the address and port number  indirectly
indicate where the offerer wants to receive RTCP reports.  Unless there
is an explicit indication otherwise, reports are sent to the port number
one higher than the number indicated. The IP address and port present in
the offer indicate nothing about the source IP address and source port
of RTP and RTCP packets that will be sent by the offerer".

Currently in RFC2327 (and updated SDP draft
draft-ietf-mmusic-sdp-new-24.txt) says that

"For an IP unicast session, the following are conveyed:
o The remote address for media

o The remote transport port for media

The semantics of this address and port depend on the media and transport
protocol defined. By default, this is the remote address and remote port
to which data **is sent**, and the remote address and remote (it is
local in RFC2327) port on which to receive data. "

Thanks for any view on this issue

 Javier Gonzalez
   UMTS Product Planning & Standards
   ' +44.(0)1628 434123. (ESN 560 4123)
   mailto:[email-masked]
   Nortel

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---

From: Colin Perkins <[email-masked]>
Date: Mon, 18 Jul 2005 20:07:54 +0100

Javier,

On 15 Jul 2005, at 16:54, Javier Gonzalez Gallego wrote:
> I have found 2 sentences that seems contradictories in RFC 2337 and  
> in RFC 3264 regarding the use of the IP address and port in the SDP  
> offer.
>
> Based on RFC 3264, the IP address/source indicated by the offerer  
> are the ones to be used to "receive" media. Especifically it says  
> later "For recvonly and sendrecv streams, the port number and  
> address in the offer indicate where the offerer would like **to  
> receive** the media stream.  For sendonly RTP streams, the address  
> and port number  indirectly indicate where the offerer wants to  
> receive RTCP reports.  Unless there is an explicit indication  
> otherwise, reports are sent to the port number one higher than the  
> number indicated. The IP address and port present in the offer  
> indicate nothing about the source IP address and source port of RTP  
> and RTCP packets that will be sent by the offerer".
>
>
> Currently in RFC2327 (and updated SDP draft draft-ietf-mmusic-sdp- 
> new-24.txt) says that
>
> The semantics of this address and port depend on the media and  
> transport protocol defined. By default, this is the remote address  
> and remote port to which data **is sent**, and the remote address  
> and remote (it is local in RFC2327) port on which to receive data. "

I don't see any contradiction. The device making the offer is saying  
"send data to this address and port", and that address and port forms  
the remote address for the answering device. You need to look at it  
from the viewpoint of the device that receives the SDP.

Colin