regarding the statement made by Jon that SSM is a subset of PIM-SM, Isnt it
true that SSM just refers to providing a host with the multicast session
from one particular source even if the underlying protocol scheme is DVMRP
or even OSPF. As far as I know, SSM has more to do with the IGMPv3 then to
From: Jon Crowcroft
Sent: Wednesday, March 07, 2001 7:11 PM
To: Ali Boudani
Cc: idmr(_at_)CS(_dot_)UCL(_dot_)AC(_dot_)UK; ietf(_at_)ietf(_dot_)org
Subject: Re: Multicast
In message <3AA60F02(_dot_)2FE41239(_at_)irisa(_dot_)fr>, Ali Boudani typed:
Isnt SSM just a particular case of PIM??
the right place for this discussion is
SSM is a subset of PIM SM, roughly, and relies (sort of) on IGMPv3 (at
least on a subset of equiv. functionality).
It is the specifications for just specific sources but they arent
the multicast in general.
am I right ?
not quite - i dont think the whole IETF list is the right place for
this one - see
i think since the ssm work is close to done, we'll see work resume on
bidir (s/cbt/pim-bidir:-) soon , and similalrly in the RMT work
a lot of building blocks are close to done (prob. about a year) then
we'll see some work on multiple source (the latent demand for multiple
source applications is imho underestimated, but until we can fix the
more immediate problems with supporting 1-many, we can't really expect
people to deploy many-to-many extensively- other problems being
addressed are concerned with having good solutions for multicast security
and for many-to-many, for congestion control (to meet transport area
i think (but of course i am usually wrong) that we may see progress on
this in 2002...
Jon Crowcroft wrote:
In message <3AA60C4B(_dot_)58AA4CFC(_at_)irisa(_dot_)fr>, Ali Boudani
>>First the CBT protocol was created to use shared tree solutions
>>DVMRP and the other dense mode protocols werent scalable. there were
>>many problems with CBT (which is bidirectional) so PIM-SM was
>>which provide some switching (between shared tree and source tree).
>>after that there is some discussions about the bidirectional PIM,
>>is like CBT.
>>Are we in circle here or what ??
not really. the mainstream current multicast action is concentrating on
single source (and on single source reliable multicast transport)
since we didn't feel we understood all the complications of ANY of the
multiple source schemes for IP or reliable....(e.g. interdomain
routing, and multiple source semantics for reliable) -
there were'nt really "problems" with CBT apart from we never managed
to get a router vendor to committ to an implmenetation which we could
deploy and learn from - tony ballardie got a lot of the details out,
but the two implementaions i know of never saw light of day.....bidir
pim is cool, bgmp is cool, but action in implementation/details/spec
is waiting on getting the PIM SSM stuff completely shaken down....
its all part of a good learning experience and (as any good s/w
engineer might say) its the norm:-)