Re: int-serv over e.g. ATM

[Mark W Garrett <[e-mail]>]

Juha,
 > .... how can the source figure out by looking into qos only if it
 > should send the the rsvp request to the router or create a direct vc?

 > ....so my rule would
 > be "switch always when you can and route if you can't", i.e., that
 > shortcut would be the default.

I don't see any architectural problem here.  Unless you're
saying that routing needs to explicitly know something about
QOS.  That's a nice concept, but I don't think we're there
yet.  (Is there a philosophical or architectural argument
against having IP routing account for QOS/TM requirements
some time in the future?)  RSVP now works under the
assumption that routing is distinct and preceeds the
resource reservation.

If you are saying a good implementation of the edge box
should be able to pick the direct path rather than an
circuitous one, well, that's obvious.  I think you
misunderstand something about rsvp.  You don't have to go
through a router to be using the rsvp/int-serv functionality
for QOS.  The case where the host interface knows that there
is a direct ATM path with appropriate QOS to the destination
and it uses that route, is a perfectly good, if degenerate,
instance of rsvp.

 > by the way, if there are several routers on the path, how can the source
 > be sure that the routers all support rsvp?  does rsvp routing protocol
 > provide information about the whole path to the source?
 > -- juha

This is again a non-problem, at least architecturally.  The
link going toward a portion of the Internet which doesn't
have rsvp can only carry best-effort traffic.  It's like
connecting TM4.0 capable ATM switches to UNI3.1 switches.
You just don't have ABR capability available on that path.
(Maybe there's a more complex answer to this, but I think
that's right to first order.)

-Mark

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