The IP over ATM Mailing List Archive by date

[rcoltun@fore.com (Robert Coltun)]

Bert,
	Sorry I probably wasn't clear.

>Rob, I think it is a "given" that one could subdivide the IP net into 100 
>LISs each with 100 hosts, especially if we then have RFC-1577-style 
>routers between them.

No routers (i.e., no IP forwarding) between them.
Systems that are running routing protocols that are there for the
sole purpose of resolving cut-through paths.
I think we are talking about similar things but another way of organizing
the internals of the ATM network.

>To me, this is not an interesting case. Put another 
>way, if we rely on IP mechanisms to route traffic over large ATM clouds, 
>what does that say about ATM? It says that by itself it's basically 
>inadequate. And if we need IP routing to wade through the ATM cloud, 
>pretty soon one wonders why bother with ATM.

>What I was trying to show, though, is that the IP prefix is not necessary
>for routing messages within an ATM framework. The IP prefix would be used 
>for routing outside datagrams _to_ the ATM periphery, and then the prefix 
>becomes just overhead. Unless we have no faith in the NNI, the IP prefix
>is unnecessary within the ATM medium. What I find interesting is that ATM
>_can_ provide, all by itself, the mechanisms for routing traffic over very 
>large areas, so that to an IP user this would look like a gargantuan 
>flatnet. Further, if we allow ourselves some routing inefficiencies (not 
>loops, mind you, but the possibility of longer data paths than perfect 
>routing might create), this IP-ATM net can also be interconnected with the
>normal Internet.
>
>My faith in the NNI, especially a public NNI, comes from the fact that the 
>global telephone system works remarkably well with an enormous number of 
>subscribers. Much greater than the number of Internet hosts, so far at 
>least. Now, one could certainly protest here, pointing out that the 
>telephone routing of today doesn't have to worry about multiple QoS levels 
>and the like. Agreed, but then again IP routing doesn't either.

As you state big phone systems are organized by prefixes so there is
aggregation. In fact, I understand that switches may service more than one
exchange so there is aggregation within the same switch. BUT they don't
flood (to the other switches) the total list of end-systems
that they service to the other switches. I think my model still holds
that depending on some administrative criteria you are assigned to
some some local exchange or LIS.

Thanks,
---rob