Subject: Re: SIP, RTSP: sequence numbers

From: Rob Lanphier <[email-masked]>
Date: Mon, 25 Aug 1997 20:39:46 -0700

At 08:12 PM 8/25/97 -0400, Henning Schulzrinne (BL) wrote:
>Suggestion: Move RTSP timestamp from request-line to Sequence: header,
>making the RTSP request/response line conformant with HTTP (and SIP).

This is agenda item 1f from Munich, quoted below:

   1f. Sequence number moved to the header fields
   
   Once upon a time, both SIP and RTSP had a sequence number in the top line
   of the request (and the response), and HTTP didn't.  Now only RTSP has
   this.  It's been suggested that we move this down to the RFC822 fields.
   This may be a bad idea changing this at this in RTSP at this stage, unless
   there is a strong feeling that it should be changed (this is my personal
   bias-RL).  Henning may wish to comment on this :)

Based on the conversation in Munich, my bias is still to leave it the way
it is (nobody stood up in defense of changing either protocol).  There were
many in Munich who felt that RTSP is a different protocol and hence
deserves its own syntax.  I feel that the sequence number is more
fundemental than your run-of-the-mill header field, and so affording it a
special place is a good thing.

Is there anyone who wasn't in Munich who would like to comment (or is there
anyone who was in Munich who is changing their mind?)

BTW, "timestamp" is accurate.  It is a sequence number in that line.

Rob
----
At 08:12 PM 8/25/97 -0400, Henning Schulzrinne (BL) wrote:
>Suggestion: Move RTSP timestamp from request-line to Sequence: header,
>making the RTSP request/response line conformant with HTTP (and SIP).
>
>Reasoning: this makes it possible to build a common parser for HTTP, SIP
>and RTSP, easily. It seems strange to have two different ways of doing
>timestamps within the same WG. (SIP does not currently need timestamps
>[although only if we ignore certain race conditions such as INVITE
>overlapping with BYE to cancel call], but it has been equipped with
>that, just in case new methods might. Some of the possible uses in the
>PINT context suggest that.)
>
>Comments?
>
>(This needs to be resolved expeditiously.)
>-- 
>Henning Schulzrinne         email: [email-masked]
>Dept. of Computer Science   phone: +1 908 949 8344 (at Bell Labs)
>Columbia University         fax:   +1 212 666-0140
>New York, NY 10027          URL:   http://www.cs.columbia.edu/~hgs
>
>
---
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/help/firewall
For more information on RTSP:                     http://www.real.com/rtsp

---

From: Philipp Hoschka <[email-masked]>
Date: Tue, 26 Aug 1997 11:44:38 +0200

>making the RTSP request/response line conformant with HTTP (and SIP).

yes, please !

when I showed the RTSP spec to our jigsaw architect (W3C http server),
this was a thing he absolutely hated, because it meant that the
Jigsaw parser would have to be rewritten compeletely.

-Philipp

---

From: [email-masked] (Anup Rao)
Date: Tue, 26 Aug 1997 17:21:52 -0700

> Jigsaw parser would have to be rewritten compeletely.

  I don't quite understand this, and here's why:

Case 1: Control channel over TCP - In this case it can be argued that
you can just ignore the sequence number. I should think the code change,
if any is minimal.
Case 2: Control channel over UDP : Since the control channel is now not
a stream based one, the changes to Jigsaw would be significant
regardless. I'll buy that it is possible to do this in a manner
independant of whether the control channel is UDP or TCP, but still dont
understand why the sequence number being in the request line would imply
a significant rewrite.

--
-----------------------------------------------------------------
  Anup Rao
  Member Of Technical Staff
  Netscape Communications Corp.
  email : [email-masked]         Phone : (415) 937 3129
-----------------------------------------------------------------

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From: Stephen Casner <[email-masked]>
Date: Tue, 26 Aug 1997 17:53:27 -0700 ()

> making the RTSP request/response line conformant with HTTP (and SIP).

I don't have a strong feeling about this issue.  Commonality of the
parser seems like a reasonable goal.

One possible downside is that there might be simple implementations
that are just looking for success/failure in the response and could
ignore the header fields.  Such an implementation would want the
sequence number on the response line to match up with the request.
But perhaps such an implementatin is unlikely -- maybe all will do a
full syntactic parsing first.
							-- Steve

---

From: Henning Schulzrinne <[email-masked]>
Date: Wed, 27 Aug 1997 19:01:06 -0400

> understand why the sequence number being in the request line would imply

In my little Java exercise of a generic SIP/RTSP/miniature-HTTP server,
the SIP and RTSP parsers subclass the HTTP parser. All three operate on
complete messages, so it doesn't matter whether the message was
delivered by UDP, TCP or punch cards. (After all, the behavior is
exactly the same, in terms of messages returned.) The HTTP parser class
takes care of the request/response line parsing.

With the sequence number as is, I can't do this as easily, as things are
different for RTSP.

-- 
Henning Schulzrinne        email: [email-masked]
Dept. of Computer Science  phone: +1 212 939-7042 (@Bell Labs: 908 949
8344)
Columbia University        fax:   +1 212 666-0140
New York, NY 10027         URL:   http://www.cs.columbia.edu/~hgs

0027         URL:   http://www.cs.columbia.edu/~hgs