Subject: [MMUSIC] RTSP: Can I specify multiple host address in RTSP 2.0 dest_addr field?

From: Kylin Wei <[email-masked]>
Date: Thu, 19 Oct 2006 18:44:00 +0800

Dear all:
Can I specify multiple host addresses in RTSP 2.0 dest_addr field in the
unicast mode?
For example: 
C->S: SETUP rtsp://example.com/foo/bar/baz.rm RTSP/2.0
      CSeq: 302
     Transport: RTP/AVP;multicast;mode="PLAY",
     RTP/AVP;unicast;dest_addr="192.0.2.5:3456"/
"192.0.2.5:3457";"192.168.1.2:3456"/
"192.168.1.2:3457";mode="PLAY"

Thanks in advance!

Kylin Wei 

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From: Magnus Westerlund <[email-masked]>
Date: Thu, 19 Oct 2006 14:05:28 +0200

>      RTP/AVP;unicast;dest_addr="192.0.2.5:3456"/

No, not as you specify it. Currently RTSP allows the following ways and 
reason to provide multiple address.

1. Within a dest_addr there be one or more addresses. The reason that 
they may be multiple address is to allow the transport to define two 
address if need. This is fully scooped by the transport protocol 
specified. So for RTP/AVP there is allowed to be one or two addresses 
specifying destination for RTP and RTCP.

2. One may use multiple transport specifications. Each transport 
specification may specify different destinations and protocols and 
parameters. However the server will select the first that it can fulfill.

Are you considering the above, or do you want to have it for some other 
purpose? For other purposes is currently not allowed. If you are 
considering to have one RTSP session that delivers media to multiple 
destination host that has some issues. The first is about configuring 
destination ports for a host the session is not running from. The second 
is about the security issues with such a solution. The denial of service 
issues with allowing unchecked delivery is very serious.

I would like to know a bit more on what you consider to do.

Cheers

Magnus Westerlund

Multimedia Technologies, Ericsson Research EAB/TVA/A
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S-164 80 Stockholm, Sweden | mailto: [email-masked]

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From: Kylin Wei <[email-masked]>
Date: Fri, 20 Oct 2006 10:50:30 +0800

Hello Westerlund:

I'm thinking if one can order a program for others. For example one order a
football match video record for some of his friends. So they can watch the
same program at the same progress. Perhaps my use case is not perfect. 
As you had said, there are two issues. But RTSP also allow specify
destination host which is not session originator, so I think specifying
multiple destination hosts should be allowed.
By the way, perhaps the description of dest_addr attribute in rfc2326bits
should be made more unambiguous.

Kylin Wei 
> -----Original Message-----
> From: Magnus Westerlund [mailto:[email-masked]]
> Sent: Thursday, October 19, 2006 8:05 PM
> To: Kylin Wei
> Cc: [email-masked]
> Subject: Re: [MMUSIC] RTSP: Can I specify multiple host address in RTSP
> 2.0dest_addr field?
> 
> Kylin Wei skrev:
> > Dear all:

---

From: Magnus Westerlund <[email-masked]>
Date: Sat, 21 Oct 2006 16:51:59 +0200

> same program at the same progress. Perhaps my use case is not perfect. 

Well the problem is that it doesn't work as you propose. As the inviting 
party can't allocate resources, for example ports the the receiving 
entity what you propose can't work. The reasonable thing to do is to 
send the URI to the party you like to invite. If actually like to have a 
session where a single entity controls what is shown, then consider to 
use a multicast address. I think the easiest way of accomplishing what 
you propose is a SIP based service where you can invite your friend into 
the session and then have an application service that forwards the 
streaming traffic to all participants you invited. Something done 
completely in RTSP needs massive extensions. Some which I don't think 
are particular suitable. Like how to resolve the rendezvous with the 
friend.

> multiple destination hosts should be allowed.

Well, if you read the security issues with inviting non session 
originators you see that this should not be allowed unless you actually 
have a solution to this issue. However the main issue is to know where 
to transmit. So if you really are interested in resolving this within 
RTSP then please write an extension draft for this.

> should be made more unambiguous.

I have added the following to first paragraph of the dest_addr 
definition on page 98 of draft-ietf-mmusic-rfc2326bis-13.

Note, only a single destination entity per transport spec is intended. 
The usage of multiple destination to distribute a single media to 
multiple entities is unspecified.

Cheers

Magnus Westerlund