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Re: MAE West
From: Stephen Stuart <stuart () pa dec com>
Date: Mon, 14 Jul 97 10:14:16 -0700

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

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.


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