Q: In my new position, I will be responsible for designing and overseeing the implementation of the UTP cable plant for a new 2000- to 4000-station network. My objective is to design a structured system that is flexible and also conforms to industry standards. I reviewed the tia/eia-568a standard and have put together a proposed design.
Although the patch panel is in the same closet as the termination blocks and equipment, I consider the cables between the patch panel and termination blocks to be "backbone" cables. Using this logic and the backbone hierarchical topology model in tia/eia-568a, I believe the design is acceptable as long as cable-distance requirements are observed. Several co-workers think the design does not comply with the standard, and I need an expert opinion. Can you advise if this design complies with tia/eia-568a?
John Meisner, Penn State M.S. Hershey Medical Center
Hershey, PA
A: According to tia/eia-568a, the function of backbone cabling is to provide interconnections between telecommunications closets, equipment rooms and entrance facilities within the telecommunications cabling system structure.
The cable between the outlet/connector and the horizontal crossconnect is horizontal cable, and the cable between the hub and the patch panel is an equipment cable. The cable between the second connecting block and the patch panel--the one you designate "backbone" cable--is not covered in tia/eia-568a.
The tia/eia-568a standard requires that backbone cabling use a hierarchical star topology and that it have no more than two hierarchical levels of crossconnects.
This means that each horizontal crossconnect in a telecommunications closet is cabled to a main crossconnect or an intermediate crossconnect, then to a main crossconnect. Following your logic one step further, the hub is now either a main crossconnect or an intermediate crossconnect--which it is not.
Now that we have worked through the logic and standard arguments, I think what you really want is to design a cabling system that will provide a robust channel. The channel described in Annex E, section E.2, of tia/eia-568a includes a work-area cord, a telecommunications outlet/connector, up to 90 meters of balanced UTP cable, an optional transition connection close to the work area, a horizontal crossconnect consisting of two connecting blocks or patch panels in the telecommunications closet, and an equipment cord.
The design in your diagram adds a third piece of connecting hardware and another cord or cable .
You should either terminate the horizontal cable on a connecting block or a patch panel and patch directly into the hub or use an equipment cable with an 8-pin modular connector only on one end, terminating the unconnectorized pairs on a connecting block or on the back side of a patch panel and then jumper or patch block to block or patch panel to panel (see crossconnect diagram above).
This does not mean that your design would not support some or even most applications available today, but applications of the future are being designed assuming that there is an Annex E-compliant channel available.
Donna Ballast is a communications analyst at the University of Texas
at Austin and a bicsi registered communications distribution designer (rcdd). Questions can be sent to her at Cabling Installation & Maintenance or at PO Drawer 7580, University of Texas, Austin, TX 78713; tel: (512) 471-0112, fax: (512) 471-8883, e-mail: ballast@utexas.edu.
