Subject: Re: [MMUSIC] RTSP REDIRECT

From: [email-masked]
Date: Thu, 16 May 2002 16:33:06 +0200

Why exactly do you not consider the possibility that a streaming server
would need to *redirect* in the middle of a (long) session because
some maintenance work has to be performed and it is going to be shut down 
?

Philippe Gentric
Software Architect
Philips MP4Net
[email-masked]
http://www.mpeg-4.philips.com

Magnus Westerlund <[email-masked]>
Sent by: [email-masked]
05/16/2002 14:40

        To:     IETF MMUSIC WG <[email-masked]>
        cc:     (bcc: Philippe Gentric/MP4-SUR/CE/PHILIPS)
        Subject:        [MMUSIC] RTSP REDIRECT
        Classification: 

Hi Oliver, and others!

I will try to summarize my view of how a server should do redirects.

3xx Responses:
The server should use this to signal the client that it should go find 
the media somewhere else. This answer can be used on the methods that do 
inquires regarding the media or tries to establish a session, i.e. 
OPTIONS (with media URL), DESCRIBE, SETUP, and perhaps ANNOUNCE. It 
should not be used when a server has an already established session and 
needs to move that session to another server, i.e. don't use them on 
PAUSE, PLAY, RECORD.

The client after receiving a REDIRECT must restart its work on getting 
session information and setting up the session.

REDIRECT request:
This method shall be used when the server needs to move already 
established session from this server. So it shall not be used unless 
there is a session identifier to reference. The redirect request SHOULD 
use contain the session control URL and MUST include a session header. 
This enables the client a unambiguous identification of which session it 
should move.

I don't know if the server should go directly to INIT after receiving 
the response from the client on the REDIRECT. This would allow the 
server to reclaim any resources as fast as possible. Alternatively the 
server should wait for a teardown, but this seem to waste a round trip 
of time. But as both behaviors are hinted in RFC 2326 it needs 
clarification.

When a client has received a REDIRECT request and acknowledge the 
redirect it must assume that the session does no longer exist. The 
exception is if a range header was part of the request, and in that case 
it will be without a session at the specified moment. So after receiving 
a redirect the client must start from scratch to establish a new session 
at the given location.

Use of location header: My opinion is that is should be a complete RTSP 
URL.

Use of Range header: Also how the Range header shall be interpreted 
together with REDIRECT needs to be clarified. As the desired behavior 
may vary I think we need to be a little bit cleaver here. If a range 
header is included and contains a time in UTC it shall be interpreted 
that the server will serve this client until that UTC time, and after 
that time the client needs to establish a new session at the given 
location. If a SMPTE or NPT time is given the session will end when the 
playback reaches the given point in the media. So in the case the client 
rewinds to the start before reaching specified media point the session 
will remain. By using UTC time the server can signal that I can't handle 
your request further than e.g. until 18.00 today. Using NPT will allow a 
server to redirect a user due to limitations of the media, e.g. charging 
for rest of movie.

Cheers

Magnus Westerlund 

Multimedia Technologies, Ericsson Research ERA/TVA/A
----------------------------------------------------------------------
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Torshamsgatan 23           | Fax   +46 8 7575550
S-164 80 Stockholm, Sweden | mailto: [email-masked]

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---

From: Magnus Westerlund <[email-masked]>
Date: Tue, 21 May 2002 10:17:37 +0200

Hi Philippe,

Yes, I am definitely considering that case. It is done by using the 
REDIRECT request. Your example is a good reason for moving already 
established session to another server.

/Magnus 

[email-masked] wrote:

> some maintenance work has to be performed and it is going to be shut 
> down ?
>
>
>
> Philippe Gentric
> Software Architect
> Philips MP4Net

-- 

Magnus Westerlund