Do ATM-based Exchange Points make sense anymore?

Sun Aug 11 22:26:18 UTC 2002

Paul just hit on it.   At how many layers do you want protection, and 
will they interfere with each other.  Granted not all protection 
schemes overlap.  If there if not a layer 1 failure, and a router 
maintains link0 but the card or routers has somehow failed and is no 
longer passing packets, I suppose that would have to be caught at 
layer 3.

At an (MAN) exchange pt based in S. Fl, the technology is a 
multi-node area exchange point (layer 1 technology) based on dwdm and 
optical switches.  The detection of nodes and failures is done with 
enhanced-OSPF.  On testing, failure between the farthest two nodes 
and recovery took 16ms (approx 95miles dist btw nodes).

Each individual circuit has a choice of protection level.  This 
allows for no protection for any of a number of reasons.  One may be 
to not interfere with a protection scheme at a higher level.  While 
the switches do use OSPF for detection and recovery, they also use 
MPLS for reservation of bandwidth.  None of this information is 
passed onto the customer routers however.

It seems there should be a clear delineation btw the layers and what 
protection schemes should run at each.  I also believe in separation 
of church and state if u will, router companies should play in their 
space while optical companies show stay in theirs.  While it makes 
sense for some information to pass btw differing types of equipment 
(such as ODSI protocol or UNI 1.0) integration of the protection 
schemes runs a high degree of a cascade failure, or susceptibility to 
an exploit attach.

As an added thought, the same MAN exchange point can do intranode 
connections (hairpinning).  So that the same node that is used in 
internodal transport and peering, can also be used within a colo as 
an intelligent cross-connect box.  This would allow for visibility 
and monitoring within the colo and even customer network management 
of their cross connects.

I suppose the discussion is what do you want from your exchange pt 
operator and what do you NOT want.  Many people would not feel 
comfortable that circuit operators have visibility and maintain stats 
on even NUMBER of packets passed....

dd

At 9:21 +0000 8/10/02, Paul Vixie wrote:
>warning: i've had one "high gravity steel reserve" over my quota.  hit D now.
>
>>  The issue I'm trying to address is to figure out how to extend the 
>>robustness
>>  that can be achieved with tuned IGP's with subsecond convergence across
>>  an exchange point without suffering a one to five minute delay blackholing
>>  packets.
>
>why on god's earth would subsecond anything matter in a nonmilitary situation?
>
>are you willing to pay a cell tax AND a protocol complexity tax AND a device
>complexity tax to make this happen?  do you know what that will do do your
>TCO and therefore your ROI?  you want to pay this tax 100% of the time even
>though your error states will account for less than 0.001% of the time?  you
>want to have the complexity as your most likely source of (false positive)
>error?
>
>>  As far as I understand, this "complexity" just got added with Neighbor
>>  Discovery on IPv6.
>
>if so, then, you misunderstand.
>--
>Paul Vixie

-- 

David Diaz
dave at smoton.net [Email]
pagedave at smoton.net [Pager]
Smotons (Smart Photons) trump dumb photons