Subject: RTSP Caching proxies

From: Denis Serenyi <[email-masked]>
Date: Fri, 28 Jan 00 09:56:16 -0800

I'm a newbie on this list, so pardon if this is not the proper forum...

I'm an engineer at Apple working on the QuickTime Streaming Server & 
Darwin Streaming Server Project, which includes an implementation of RTSP 
and uses RTP.

We've recently been talking to several companies who want to write RTSP 
caching proxies. Though RTSP does take into account & attempts to solve 
some of the issues that a caching proxy would run into, we have had 
requests to add extensions to our implementation of RTSP / RTP to make 
their lives easier.

We've spent some time gathering their feedback to try and come up with a 
common RTSP caching solution that meets everyone's needs. In the past 
couple of days I've been working on coming up with a preliminary spec 
based on this.

However, we don't want to reinvent the wheel, so my first question is, is 
there already any effort to provide a "streaming media caching" protocol? 
Or anything similar?

If yes, please point me at any documentation on this.

If no, I would be happy to share in more detail exactly what problems 
with RTSP / RTP we are attempting to solve for these caching proxy 
vendors, and get feedback on 1) whether these changes are really 
necessary and is there some better way to provide this functionality. 2) 
if these changes are necessary, how to best go about implementing them.

Thanks in advance,
Denis Serenyi
QuickTime Streaming Server Engineering

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From: Reza Rejaie <[email-masked]>
Date: Sun, 30 Jan 2000 00:03:32 -0500 (EST)

Denis,

We have been working on proxy caching mechanisms for layered encoded
multimedia streams. The idea is to use proxy caches to improve
delivered quality and reduce the load on the network/server.
Although we have focused on layered-encoded streams, the proposed
mechanism can be applied to any multimedia stream as long as it
has an internal structure to adjust its quality.

More details can be found in;

Multimedia Proxy Caching Mechanism for Quality Adaptive Streaming 
Applications in the Internet
Reza Rejaie,  Haobo Yu, Mark Handely, Deborah Estrin
To Appear in Proceedings of IEEE INFOCOM'2000
http://netweb.usc.edu/reza/papers/infocom00.ps

There are couple of commercial multimedia-capable caches that do
not provide any technical information. I suspect that they treat
multimedia streams similar to web objects, but they are able to
properly playback those objects for an interested client on a hit,
i.e. They do *not* address the notion of quality improvement.

We have not looked into required extensions in RTP, RTSP to support
our schemes but I would be interested in discussing those issues.

ReZa

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From: [email-masked] (Alagu Periyannan)
Date: Sun, 30 Jan 2000 11:20:44 -0800

Hi all,

Entera has done some work in the area of RTSP caching.

We are very interested in open standards for media caching and can make
our current proposal available as an IETF draft to aid this discussion.

The 2 keys problems that need solutions and possibly extensions to RTSP
are,

(a) Replicating a loss-less copy of the media from an origin server into
a cache.

(b) If we do (a) how do we solve copyright issues (because media content
is considered by most people as more valuable than web pages.)

Other issues such as cache coherency, access logging, authentication,
etc. can easily be solved within the current RTSP protocol
specification.

-Alagu

Alagu Periyannan
[email-masked]