Subject: RE: Allocating state in RTSP DESCRIBE

From: "Anders Klemets (VXtreme)" <[email-masked]>
Date: Wed, 24 Sep 1997 10:39:09 -0700

On Wednesday, September 24, 1997 9:14 AM, [email-masked]
[SMTP:[email-masked]] wrote:
> The If-Match header(Section 12.22) accomplishes this.(Also see
> corresponding etag definition in Appendix C).

Interesting, I didn't realize that these things had been added to the
RTSP spec.  So the idea seems to be that when the client sends a SETUP
command, it would include a header line like this:

If-Match: "random-sdp-no-7"

The string "random-sdp-no-7" is an "entity tag" that is obtained from
the presentation description.  According to Appendix C, an SDP record
would need to contain the line

a=etag:"random-sdp-no-7"

That's fine, I guess.  It allows the client to obtain the entity tag
even if it downloaded the SDP record from a web server, or through some
other means.  But I am worried that not all presentation description
formats may have a well-defined way to specify an entity tag.  RTSP
should not rely on that any particular presentation description format
should have such a capability.  So for correctness, and symmetry, I
think RTSP should also allow the HTTP 1.1 "Etag:" header line.  It is
used to specify the entity tag in HTTP 1.1.  

Anders