Re: Use of SAP in a PIM SSM Network

[Toerless Eckert <eckert@cisco.com>]

> Toerless presented an argument that session announcements wouldn't
> scale. I presented a counter argument, a scheme which does scale, which
> no-one has  refuted.

Just because my email server was upgraded ;-)

I hope that i just said that session announcements in the way it is currently
handled in the Internet does not scale. Session announcements by themselves
will scale, but by doing so, we implicitly need to introduce directory like
selection mechanism that simultaneously can give us all the information
to use SSM too.

All the examples cited (cable-tv, wireless devices) show that the session
information you may want to receive in a broadcast style are limited
in quantity (certainly not "everything from the internet"). Also they
typically will be managed by someone providing the access, like AT&T for
the cable-tv or whoever gives you the wireless connectivity. You may not
call it web anymore, but the more you get into ubiquitous devices, the more
will you see that they all have some initial portal to services.

In this space, yes, you may want to "broadcast" session information, and 
yes, you can easily use SSM, because you can source that broadcast from
a well-known source address. Heck, why not use our beloved anycast mechanism ?

The problem with broadcasting session information is that nobody in his sane
mind (hopefully) should think that you would want to get a flat, 
undifferentiated broadcast of all the sessions in all the world, which is
what you would get today with SAP. And once you are putting structure into
this, then you say that you want to select which part you want to receive,
and that already means that you have keys for selection, and those keys
just need to map to the source addresses originating the broadcast selection,
so that SSM can be used.

Cheers
	Toerless