Subject: RTSP Cache control

From: John Carlton <[email-masked]>
Date: Mon, 26 Oct 1998 21:47:06 -0800

The RTSP spec talks about the Cache-Control general header field in section
12.8. But this section specifies that cache directives should only be
specified in a SETUP request and its response.

Can anyone fill me in on the reasons why the DESCRIBE request/response
should not also specify Cache-Control?

If this was required the server could specify whether content can be served
from a cache before resources are allocated by the SETUP, which would be
much more efficient. If the content can come from the cache a proxy can
save one round trip time by knowing this when the DESCRIBE response is
received. Furthermore, the SETUP request could be sent with a special
"accounting-only" transport that says to the server "do a lightweight
SETUP, I won't be asking you for any data". The proxy then uses the ports
it has allocated to serve data from the cache (the cache could even speak
RTSP if desired).

In short, both the proxy and the origin server can be more efficient if
Cache-Control directives are exchanged at DESCRIBE time. It seems to me
that information about whether a particular resource is cacheable or not,
along with its last modified time or staleness, could be considered part of
the media initialization phase.

Any thoughts?

thx

jc