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Re: MAE West
From: "Jay R. Ashworth" <jra () scfn thpl lib fl us>
Date: Mon, 14 Jul 1997 13:40:36 -0400

On Mon, Jul 14, 1997 at 10:14:16AM -0700, Stephen Stuart wrote:
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. 

If this is true, then the Layer 2 bandwidth aggregation design is
pretty weak, no?

For example, (and yes, I know there's a world of difference) a MLPPP
link is at (effectively) layer 2 (if not 1.5), and if one side of the
link drops, the other side will carry what it can.

-- jra
Jay R. Ashworth                                                jra () baylink com
Member of the Technical Staff             Unsolicited Commercial Emailers Sued
The Suncoast Freenet      "People propose, science studies, technology
Tampa Bay, Florida          conforms."  -- Dr. Don Norman      +1 813 790 7592

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