Re: Use of SAP in a PIM SSM Network

[Marshall Eubanks <tme@21rst-century.com>]

Toerless Eckert wrote:
> 
> > Encouraging the use of static Class D addresses sets a bad precedent
> > and I don't think we should be encouraging this. The broadcasters
> > and content providers have static host names which can be
> > used for rendezvousing and the source address and group address should
> > be able to float as needed to meet demand. End users will not be
> > aware of the group address being used under most circumstances
> > anyway.
> 
> Agreed. What i was thinking of as a possible operational improvement would
> be to have some operational SSM document in which to recommend a specific
> randomn number generator for selecting the SSM address to use, and have this
> generator be seeded by some combination of AS number and source ip address
> to be used for the channel, so that we gett less MAC-level ambiguities of
> the SSM groups being used.
> 
> Would just need someone with more insight and time to come up with good
> recommendaations for this. I think if you could show just by some good
> simulation, that you could get collision rate at MAC layer down by a few
> factors over completely random assignment, then it would be good enough
> to have this for all practical purposes.
> 
> Dunno how much one could practically achieve with this though...
> 
> Cheers
>         Toerless


SSM in intended for (or, is at least, ideal for) BROADCASTING. 
In the real world, broadcasters
stay up for years at a time. They don't like down time, even for seconds.
They will NEVER want to renumber their class D addresses - these will
get embedded in too many places (including .pls type files at the receivers)
to make any such transition smooth.
If there is a MAC layer collision, for any reason, they will want a fast
means of resolving it. Now, I am sorry,
but this sounds awful much like a static address to me.

SSM is very attractive for broadcasters. Please do not hinder it by insisting
on some theoretical purity that does not fit their business model.


                                   Marshall



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