Subject: A few questions

From: Ning Wang <[email-masked]>
Date: Thu, 19 Apr 2001 10:48:37 +0100

Hello,
   I have a few questions on current multicast routing implementation:
(1) IETF is now putting great efforts on SSM for one-to-many
applications. On the other hand,
Simple Multicast also belongs to RAMA style multicast, but why isn't it
attractive recently? I just
noticed that the last internet draft for SM is in Oct. 1999. IETF is
developing bidir-PIM, does this
mean that SM comes to its end? In fact SM successfully solves the
problem of class D address
allocation.  BTW, can igmpv3 support SM? Note that the root of the tree
in SM is a router instead
of the information source itself.
(2) For multicast applications with multi-senders we can still use SSM
model,  and additional senders
can be authorized and authenticated by the single source (root) at the
APPLICATION level. How
about bi-directional trees? Is it possible to implement the sender
access control at the same level, or
should it be developed at the routing level?
  Thanks.

Ning Wang

---

From: Radia Perlman - Boston Center for Networking <[email-masked]>
Date: Thu, 19 Apr 2001 21:14:32 -0400 (EDT)

From: Ning Wang <[email-masked]>

	Hello,
The term "RAMA", for those for which it's not familiar, means "Root-
Administered-Multicast-Addressing", and as you observed, "Single source
multicast" and "Simple Multicast" both were RAMA-style.

As for whether igmpv3 can support it...anything can support anything
if there's enough bits. Igmpv3 has enough bits to specify "I want
to join (R,G). But I'd think an even better way to do joins would
be using something like UMTP, because it doesn't require support in
the operating system...it can be deployed as a user-level process.
And then you can also automatically tunnel across regions of the net
that don't support multicast. you don't even need a local router on
your LAN supporting multicast. The draft
   draft-finlayson-mboned-autotunneling-00.txt
explains this.

As you stated, bidirectional tree support with RAMA addressing would
be a good thing to do. Bidirectional PIM cannot use RAMA addressing
(at least as specified...anything can support anything if modified).
BIdirectional PIM (currently) requires globally unique 4-byte addressing.

As for whether it's a good time now to think about extending "single source"
for bidirectional trees, I suspect it is. Now that people are getting
used to the idea of 8-byte groups and seeing how it makes things
much more manageable, it's a natural time to get together a proposal
for reviving something like Simple Multicast. I'm not sure
what mailing list would be appropriate. Maybe idmr, though this
isn't strictly in their charter I think. Maybe SSM, though their
charter seems to be specific to unidirectional trees.

You said one slightly incorrect thing. You said that the root of the
tree in bidir-RAMA was a "router rather than the source". The root
need not be a router. It can be an endnode. The root does not
need to forward traffic. In a bidir tree, even packet appears on
every link once, so if the root is an endnode with only a single
link, then it would never forward multicast traffic. It will either
source it or receive it on its link.

	Ning Wang
	
If you want routers to enforce access control, then the access control
policy would have to be distributed by the root to the routers along
the tree. This was specified in the SImple Multicast proposal.	It
allows configuration of the policy at a single point (the tree root,
the host of the multicast group), but you do want routers to filter
unauthorized traffic.

Radia