Collapsed backbone

Q: For the past year, I have been designing a new three-story building at a national laboratory. In the beginning, I had to fight with the architects for space on each floor for a telecommunications closet. When I finally received a set of blueprints--and all the space I had fought for--I proceeded to lay out the horizontal and riser cabling scheme. Three-quarters of the way through this phase of the project, my supervisor insisted that home runs go to the first floor, where the main crossconne

Q: For the past year, I have been designing a new three-story building at a national laboratory. In the beginning, I had to fight with the architects for space on each floor for a telecommunications closet. When I finally received a set of blueprints--and all the space I had fought for--I proceeded to lay out the horizontal and riser cabling scheme. Three-quarters of the way through this phase of the project, my supervisor insisted that home runs go to the first floor, where the main crossconnect is to be located. The distances from the first-floor main crossconnect to the most distant outlet will be less than 100 meters. We will also be installing fiber to many of the workstations; these runs will be home runs to the main crossconnect, as well.

My problem is that I cannot find support for my design, which calls for a closet on every floor. According to my supervisor, the cost of equipment will be lower if we have it in one location, and there will be fewer terminations for the fiber and copper cables, and fewer crossconnects.

I am stumped. Can you make some suggestions to back up my design? Or do you agree with my boss?

Daniel M. Cocosa

Lawrence Berkeley Laboratory

Berkeley, CA

A: What your boss is mandating is so common in the telecommunications industry today that it has a name--collapsed backbone. But this is a collapsed-backbone cabling system, not a collapsed-backbone pathway system. The telecommunications closets for which you negotiated so diligently will be there for the life of the building. The cabling system will not be. Be sure to route the home-run cables through the telecommunications closets. This will allow for termination of the horizontal cabling in the telecommunications closet in the future.

I would caution you that the 100-meter length you mentioned is for the channel. TIA/EIA-568A defines 90 meters as the maximum length of cable to be installed from the outlet/connector in the work area to the horizontal crossconnect in the telecommunications closet. However, TIA/EIA-568A does not require that the telecommunications closet be on the same floor as the work area it serves.

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