Please clarify. To which network element are you referring in connection with extended lookup times? Is it the collapsed optical backbone switch, or the upstream L3 element, or perhaps both? Certainly, some applications will demand far less latency than others. Gamers and some financial (program) traders, for instance, will not tolerate delays caused by access provisions that are extended over vast WAN, or even large Metro, distances. But in a local/intramural setting, where optical paths amount to no more than a klick or so, the impact is almost negligible, even to the class of users mentioned above. Worst case, run the enterprise over the optical model and treat those latency-sensitive users as the one-offs that they actually are by tying them into colos that are closer to their targets. That's what a growing number of financial firms from around the country have done in NY and CHI colos, in any case. As for cost, while individual ports may be significantly more expensive in one scenario than another, the architectural decision is seldom based on a single element cost. It's the TCO of all architectural considerations that must be taken into account. Going back to my original multi-story building example-- better yet, let's use one of the forty-story structures now being erected at Ground Zero as a case in point: When all is said and done it will have created a minimum of two internal data centers (main/backup/load-sharing) and a minimum of eighty (80) LAN enclosures, with each room consisting of two L2 access switches (where each of the latter possesses multiple 10Gbps uplinks, anyway), UPS/HVAC/Raised flooring, firestopping, sprinklers, and a commitment to consume power for twenty years in order to keep all this junk purring. I think you see my point. So even where cost may appear to be the issue when viewing cost comparisons of discreet elements, in most cases that qualify for this type of design, i.e. where an organization reaches critical mass beyond so many users, I submit that it really is not an issue. In fact, a pervasively-lighted environment may actually cost far less. Frank A. Coluccio DTI Consulting Inc. 212-587-8150 Office 347-526-6788 Mobile On Sat Mar 29 19:20 , Mikael Abrahamsson sent:

On Sat, 29 Mar 2008, Frank Coluccio wrote:

...

We often discuss the empowerment afforded by optical technology, but we've barely scratched the surface of its ability to effect meaningful architectural changes.

If you talk to the server people, they have an issue with this:

Latency.

I've talked to people who have collapsed layers in their LAN because they can see performance degradation for each additional switch packets have to pass in their NFS-mount. Yes, higher speeds means lower serialisation delay, but there is still a lookup time involved and 10GE is substantionally more expensive than GE.

-- Mikael Abrahamsson email: swmike@swm.pp.se