Re: Simple Multicast - building a case for a BOF or WG

[Ken Carlberg <carlberg@time.saic.com>]

> On this latter point, and following up on Adam's query on costs, I'd like
> to understand the compelling application(s?) that motivate the bi-directional
> shared trees.

i don't believe there are any well-known apps, ones that we see on the
mbone and that get discussed on different multicast lists, that would
break if they couldn't use bi-directional trees.  

one can argue that DIS-type applications operate a bit better with bi-
directional trees, but they will still perform with uni-directional
trees (at least given today's number in groups, participants, and 
topology).  

outside of these 'normal' sets of applications, one thing that is 
difficult to do with uni-directional trees that use RPF checks on 
the source, is to try and tweak these tree construction designs to 
support QoS or Quality of Route (QoR).  as an example, trying to 
promote high fan-out towards the leaves of a tree is much easier
to do with bi-directional trees, where i can graft a branch onto 
any on-tree node, as opposed to constraining the graft process to
only the shortest path towards the core.

-ken