Re: MAE West

[bmanning () ISI EDU]

> > On Mon, Jul 14, 1997 at 07:27:15AM -0700, Owen DeLong wrote:
> > > > To true.  Would you care to cover the cost of replicating the 400Mbp/s
> > [ quoting Bill ]
> > > > to build in better reliability?  It appears that the owners/operators of
> > > > MAE-West are selecting an optimization path based on the assumption that
> > > > outages are infrequent and can be quickly corrected.
> >
> > > Both assumputions have been repeatedly proven false BY MFS.
> >
> > Indeed.  More importantly, Bill, he wasn't suggesting duplicating the
> > 400Mbps aggregate, but _splitting_ it; it is, after all, _already_ 4
> > separate links.
>
> The underlying physical media may be four separate links, but at L2
> it's a single 400Mb/s aggregate. If it were split up into, say two
> 200Mb/s aggregates:
>
> 1) assuming that costs favored intra-building connections, one of the
> aggregates would be selected for pruning by the spanning tree
> calculation.
>
> 2) assuming that costs favored having both aggregates in service, if
> utilization on the two aggregates was 50% on (call it) A and 100% on B,
> the 50% available on A would be wasted. Note that latency would go up,
> because spanning tree would have pruned some intra-building link would
> have been pruned in order to keep the inter-building link active. 
>
> As the risk of belaboring the obvious, of course there are issues of
> reliability and cost-effectiveness, only some of which are technical.
>
> With respect to economics, for instance: The cost to link two ports in
> the same building (better yet, the same room) is essentially the FDDI
> cable. The cost to link two ports over a wide area is that of a
> DS3/OC3. L2 is not all that different from L3 in that once you've
> spent real money on a circuit, you want to get as much use out of it
> as you can.
>
> Stephen

I think that the argument here is that there is a real need to have 
an aggregate 400Mbp/s "pipe" in service as opposed to 2 each 200Mbp/s
"pipes".  To gain the redunancy that Mr. Dave suggests, would actually
encourage the deployment  of -two- additional 400Mbp/s channels.

Then the economics arguments kick in.

-- 
--bill