Cell Relay Archive

[Jean-Philippe Martin-Flatin <jpmf@tcom.epfl.ch>]

Hi,

Thanks for your answer.

In article <869673052.17591@dejanews.com>, manfredi@arl.bna.boeing.com
wrote:
> 
> > If we assume that all VC connections in our network are short-lived,
> > then the problem is simple: as soon as the routing tables are
> > updated, connections are created using the new routes, and soon
> > afterwards all connections created prior to the routing table update
> > are released.
> 
> I would have worded that differently. I would have said that new VCs
> set up after the routing tables are updated would use the new routes.
> But VCs which existed before the routing table update would _not_ be
> torn down automatically.

Thanks for the correction, this is indeed what I meant.

> At least, that's not the normal way of doing business.
> (I suppose one could implement a special-purpose ATM network
> that way, to somehow force VCs to be torn down and re-established
> whenever a routing table change occurs.)

OK, this answers my question: you think rerouting existing long-lived
VCCs could be done, but nobody does it. Right ?

> > does it make sense to consider the rerouting of these
> > existing long-lived, bandwidth demanding VC connections ? Is it
> > something made possible at all by ATM ?
> 
> Re-routing of calls, if you use Q.2931, would only happen if the
> VC is first torn down, then re-established.

So we would need a layer above Q.2931 to first request a new VCC between
the same end nodes; Q.2931 would then create it based on the new routing
tables; then the layer above would switch the traffic from the initial
VCC to the new one, by updating lookup tables in the 2 end nodes;
finally, the layer above would ask the Q.2931 layer to tear down the old
VCC. Right ? What would this "layer above" be ?

> This is what makes circuit-switched and packet-switched systems
> different (ATM being circuit-switched).

Pardon ? Could you please elaborate on this ? For me:

- telephony is connection-oriented and circuit-switched
- ATM is connection-oriented and packet-switched
- IP is connectionless and packet-switched

The big conceptual innovation in ATM came precisely from disconnecting
the concepts of "circuit" and "connection", as far as I know.

Jean-Philippe

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Jean-Philippe Martin-Flatin                    Email: jpmf@tcom.epfl.ch
Research and teaching assistant
Telecommunications Laboratory
EPFL (Swiss Federal Institute of Technology at Lausanne)
1015 Lausanne
Switzerland
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