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Link aggregation can be used to support redundant unused links if you wish,
either explictly or by choice of distribution algorithm.

I am not sure whether you are arguing for introducing the complexity of flow
control below or not. In any case it is the wrong answer. Service is not
improved by stopping traffic flows. In any case they won't get stopped right
back to the originating application, they'll build up and get discarded in
some buffer somewhere. The right answer is to differentiate between the
services (as per .1p and Diffserv) and making sure that the higher grade
traffic levels have spare capacity (as you suggest in your first para). Then
link aggregation can be used as Fred suggests to spread the traffic around
with the result that the network can sustain higher levels of 'best effort'
or 'background ' service in the absence of failure, while satisfactorily
handling admission controlled high priority/expensive/committed traffic even
if there is a failure. That's better economics.

Net net we don't need more embedded stuff in the data link. It took us years
to figure this out, throwing out the use of X.25 and LAPB/SDLC on high speed
links, and we don't need to go back there.


> -----Original Message-----
> From:	Roy Bynum [SMTP:rabynum@xxxxxxxxxxx]
> Sent:	Friday, June 25, 1999 7:50 PM
> To:	Fred Weniger
> Cc:	'HSSG_reflector'
> Subject:	Re: OAMP Etc.
> Fred,
> Interesting that you should suggest this.  Oddly enough, having
> redundant fiber turns out to be cheaper for protocols that do not have
> active flow control.  People, operations costs, cost the carriers more
> than making use of "spare" capacity when liquidated damages are part of
> most service level agreements.  
> Link aggregation at L2 does not always map L3 path route aggregation
> because "over subscription" can not be controled in the case of a
> partial "link route" failure.  In the case using active flow control
> over bridged, not routed systems, "over subscription" should be
> controlable.  This is one of the differences between what some people
> are used to accepting as the cost of doing business, and people who are
> always chalanging the "religiously accepted" way of thinking. 
> Thank you,
> Roy Bynum
> Fred Weniger wrote:
> > 
> > Pardon my naivete, but if people start demanding idle backup paths in
> 10GbE
> > WAN links, as are to be found in SONET rings (correct?), shouldn't the
> > discussion at least include a comparison of the benefits of Ethernet
> link
> > aggregation, i.e., when multiple links are all carrying Ethernet packets
> > between two points, and if one link goes down, the remaining links
> continue
> > to carry data.  The benefit is the full utilization of all available
> data
> > paths, with no available link sitting there idle.
> > 
> > Fred Weniger
> > Product Marketing Manager, Gigabit Products
> > Vitesse Semiconductor Corporation
> > 741 Calle Plano, Camarillo, CA 93012
> > Phone: 805-388-7571   Fax: 805-987-5896
> > E-mail: weniger@xxxxxxxxxxx