Subject: SDP and RTSP related questions

From: [email-masked]
Date: Fri, 5 Oct 2001 19:12:41 +0300

Hello,
I have two questions to ask related to SDP and RTSP 

The 1st is related to the internet draft "draft-ietf-mmusic-sdp-new-03.txt",
the SDP protocol.
This draft introduces some changes to the current RFC 2327. One of the
changes that I can address right now is making both the 'e' and 'p' fields
optional. (In RFC 2326, at least one of them must be present in the SDP
information).

Since the 'version' field is still '0' in the new draft document, it is
impossible to distinguish whether an SDP content is built according to RFC
2327, or the new version, which will be defined by this draft document. This
will definitely bring some compatibility problems with the current
implementations of SDP parsers.

I am wondering if it will be a good solution to change the "v=0" field to
"v=1" in this draft, to address the difference in versions to solve the
compatibility problem.

2nd question is related to a difference in interpretation of the "c" field
in RFC 2326 (RTSP) and RFC 2327 (SDP). 

According to SDP RFC, "c" field defines the connection information and
possibly the address of the media data source, i.e. the server that sends
the media related packets for unicast case.

According to RTSP RFC, "c" field is defined as follows:

---------------------------------------------
(taken from section C.1.7 in RFC 2326)
...
C1.7 Connection Information

In SDP, the "c=" field contains the destination address for the media
stream. However, for on-demand unicast streams and some multicast
streams, the destination address is specified by the client via the
SETUP request. Unless the media content has a fixed destination
address, the "c=" field is to be set to a suitable null value. For
addresses of type "IP4", this value is "0.0.0.0".
...
---------------------------------------------

So, in the RTSP RFC the "c" field is the connection information of the
"destination" of the media stream, in other words the client. Isn't this
contradicting with the SDP RFC? Or do I make a wrong interpretation here?

I kindly request from the authors of these two RFCs to clarify these two
issues.

Best regards,

Emre Baris Aksu
Senior Design Engineer 
Application SW, Tampere

Nokia Mobile Phones
Product Creation Center Tampere / Finland
e-mail : [email-masked]
Mobile : +358 40 743 1972
Fax    : +358 10 505 7662

---

From: Colin Perkins <[email-masked]>
Date: Tue, 09 Oct 2001 22:32:15 -0400

>"v=1" in this draft, to address the difference in versions to solve the

No, I don't think so. The rationale for the change was that there are
implementations which make the 'e' and 'p' fields optional anyway, so
the change is reflecting existing practise.

>According to RTSP RFC, "c" field is defined as follows:

I'm not sure 'server' and 'client' is the right distinction to make here.
The idea is that the system which receives the SDP sends data to the c=
address. I think the two are consistent.

Colin