Subject: [AVT] RTP: Note regarding SSM

From: Stephen Casner <[email-masked]>
Date: Tue, 7 Jan 2003 15:20:38 -0800 (PST)

One of the IESG comments (this one from Harald Alvestrand) was a
request to add the following "non-normative note" at the end of
Section 6 where RTCP is introduced (i.e., just before 6.1).  Does
anyone object?

        Non-normative note:  In the multicast routing approach
        called Source-Specific Multicast (SSM), only one or a few
        senders send multicast data, and receivers may not send
        multicast.  The recommendations here accommodate SSM only
        through Section 6.2's option of turning off receivers' RTCP
        entirely.  Future work will specify adaptation of RTCP for
        SSM so that feedback from receivers can be maintained.

                                                        -- Steve

_______________________________________________
Audio/Video Transport Working Group
[email-masked]
https://www1.ietf.org/mailman/listinfo/avt

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From: Mark Baugher <[email-masked]>
Date: Tue, 07 Jan 2003 21:51:08 -0800

Steve,

At 03:20 PM 1/7/2003 -0800, Stephen Casner wrote:
>         multicast.

It has been awhile since I read the SSM I-Ds, but this does not sound right 
to me.  I scanned the documents in 
http://www.ietf.org/html.charters/ssm-charter.html and cannot find anything 
about multicast receivers being prevented from sending multicast packets (a 
multicast sender is also a receiver, right?).  SSM defines an (S,G) 
"channel" that allows receivers to select certain senders to group G.  I 
don't know where it is specified that receivers may not send multicast.

Mark

>The recommendations here accommodate SSM only

---

From: Mark Baugher <[email-masked]>
Date: Tue, 07 Jan 2003 22:06:42 -0800

At 09:51 PM 1/7/2003 -0800, Mark Baugher wrote:
>It has been awhile since I read the SSM I-Ds, but this does not sound 
>right to me.  I scanned the documents in 
>http://www.ietf.org/html.charters/ssm-charter.html and cannot find 
>anything about multicast receivers being prevented from sending multicast 
>packets (a multicast sender is also a receiver, right?).

excuse me, a sender that joins/subscribes to (S,G) is also a receiver.

Mark

>SSM defines an (S,G) "channel" that allows receivers to select certain 
>senders to group G.  I don't know where it is specified that receivers may 
>not send multicast.
>
>Mark
>

---

From: Marshall Eubanks <[email-masked]>
Date: Wed, 8 Jan 2003 06:10:50 -0500

Dear Stephen;

>         called Source-Specific Multicast (SSM), only one or a few

I do not like "a few" here. There is one sender per channel. True, there
can be multiple channels, but then it is not limited to "a few", and, of 
course,
there is nothing stopping the receivers from sending on their own 
channel.

I would change this sentence to

In the multicast routing approach called Source-Specific Multicast 
(SSM), there is only
one sender per "channel" (source - group pair), and receivers cannot use 
multicast
to communicate directly with other channel members.

>         SSM so that feedback from receivers can be maintained.
                                  Regards
                                  Marshall Eubanks

T.M. Eubanks
Multicast Technologies, Inc.
10301 Democracy Lane, Suite 410
Fairfax, Virginia 22030
Phone : 703-293-9624       Fax     : 703-293-9609
e-mail : [email-masked]
http://www.multicasttech.com

Test your network for multicast :
http://www.multicasttech.com/mt/
  Status of Multicast on the Web  :
  http://www.multicasttech.com/status/index.html

---

From: Mark Baugher <[email-masked]>
Date: Wed, 08 Jan 2003 09:22:36 -0800

At 06:10 AM 1/8/2003 -0500, Marshall Eubanks wrote:
>there is nothing stopping the receivers from sending on their own channel.
>
>In the multicast routing approach called Source-Specific Multicast (SSM), 
>there is only

I think this sentence is a good replacement.  It might be more clear to 
write "source address, group address pair" in place of "source - group 
pair" and replace "other channel members" with "members of a channel having 
a source address other than its own."

Mark

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From: Marshall Eubanks <[email-masked]>
Date: Wed, 8 Jan 2003 14:55:21 -0500

Dear Mark;

On Wednesday, January 8, 2003, at 12:22 PM, Mark Baugher wrote:

>> can be multiple channels, but then it is not limited to "a few", and, 
>> of course,
>> one sender per "channel" (source - group pair), and receivers cannot 
>> use multicast
> write "source address, group address pair" in

I agree

> place of "source - group pair" and replace "other channel members" with 
> "members of a channel having a source address other than its own."

This does not sound too clear, and is not quite correct - a receiver can 
have more than IP address -

How about

In the multicast routing approach called Source-Specific Multicast 
(SSM), there is only
one sender per "channel" (a source address, group address pair), and 
receivers
(except for the channel source) cannot use multicast
to communicate directly with other channel members.

Marshall

                                  Regards
                                  Marshall Eubanks

This e-mail may contain confidential and proprietary information of
Multicast Technologies, Inc, subject to Non-Disclosure Agreements

T.M. Eubanks
Multicast Technologies, Inc

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From: Mark Baugher <[email-masked]>
Date: Wed, 08 Jan 2003 14:13:46 -0800

hi Marshall

At 02:55 PM 1/8/2003 -0500, Marshall Eubanks wrote:
<...>
>to communicate directly with other channel members.

This sounds fine to me.

Mark

>>>><https://www1.ietf.org/mailman/listinfo/avt>https://www1.ietf.org/mailman/listinfo/avt 
>>>>
>>>                                  Regards
>>>                                  Marshall Eubanks
>>>
>>>T.M. Eubanks
>>><http://www.multicasttech.com>http://www.multicasttech.com
>>>
>>><http://www.multicasttech.com/mt/>http://www.multicasttech.com/mt/
>>><http://www.multicasttech.com/status/index.html>http://www.multicasttech.com/status/index.html 
>>>
>>>
>>><https://www1.ietf.org/mailman/listinfo/avt>https://www1.ietf.org/mailman/listinfo/avt 
>>>
>>
>><https://www1.ietf.org/mailman/listinfo/avt>https://www1.ietf.org/mailman/listinfo/avt 
>>
>                                 Regards
>                                  Marshall Eubanks
>
><http://www.multicasttech.com>http://www.multicasttech.com
>
><http://www.multicasttech.com/mt/>http://www.multicasttech.com/mt/
><http://www.multicasttech.com/status/index.html>http://www.multicasttech.com/status/index.html 
></blockquote></x-html>

---

From: Stephen Casner <[email-masked]>
Date: Wed, 8 Jan 2003 19:31:38 -0800 (PST)

> to communicate directly with other channel members.

Thanks, I'll use that.

Please note that the original wording came from Harald, but I think he
would accept this as a replacement.

                                                        -- Steve