Subject: Re: PEP Integration in RTSP

From: Rob Lanphier <[email-masked]>
Date: Mon, 19 May 1997 13:00:46 -0700

At 12:13 PM 5/19/97 -0400, Mark Handley wrote:
>HTTP has evolved to be all things to all people (kind of a universal
>transport/transaction protocol), and to need to carry an almost
>infinite variety of header fields, which is why a protocol like PEP is
>now required.
>
>Do we really believe that RTSP needs to evolve in the same way?

Here's what is driving this.  The current RealAudio and RealVideo products
have an extension mechanism in it.  This has been an absolutely vital part
of keeping the protocol sane and yet still allowing the rapid deployment of
new features.  The current RealAudio mechanism is relatively simple, and
really not unlike the "Require:" field in the current RTSP draft.

Henning was rightfully concerned that we were needlessly diverging from the
direction of HTTP by having our own extension mechanism, and proposed that
we use PEP.  PEP is more powerful than "Require:" and "Transport-require:",
and thus is more complicated.

So, based on your statement above, there are two questions here:
*  Do we need an extension mechanism?  I'm very adament that this must be a
feature of the protocol, given Progressive Networks' past experience with
this.
*  Should we use PEP?  I really think it's the right thing to do, given
that we are proposing an extension mechanism, and since the PEP authors
have clearly put a lot of thought into this problem.  However, there are
risks associated with this:  mainly, that PEP is an Internet draft, and
therefore must reach "proposed standard" before it can be a requirement of
RTSP (i.e. before RTSP can reach "proposed standard").

As HTTP has shown, not having an extension mechanism does not mean that
vendors won't add features to the protocol.  Rather, what it means is that
they will do it in ways that may break existing implementations.  I think
the best thing about PEP is that it allows unextended clients a way of
gracefully  handling extensions, and that is a very desirable feature.

Rob

---
Rob Lanphier               Voice: (206)674-2322         Fax: (206)674-2699
Program Manager-Protocols                         Email: [email-masked]
Progressive Networks-Home of RealAudio            Web: http://www.real.com
For more information on firewalls:       http://www.real.com/firewall.html
For more information on RTSP:               http://www.real.com/prognet/rt

---

From: Karl Auerbach <[email-masked]>
Date: Mon, 19 May 1997 15:53:20 -0700 (PDT)

> So, based on your statement above, there are two questions here:  * Do
> we need an extension mechanism?  I'm very adament that this must be a
> feature of the protocol, given Progressive Networks' past experience
> with this. 

It might help clarify things if we had a few concrete examples of what
kinds of things this extensibility would be useful for (and perhaps some
examples of where it wouldn't be useful.)

		--karl--