Specifies Design Requirements for Backbone Cabling

Written by Julianus Yu

ANSI/TIA/EIA-568-B specifies additional design requirements for backbone cabling, some of which carry specific stipulations, as follows:

• Grounding should meet the requirements as defined in ANSI/TIA/EIA-607, the Commercial Building Grounding and Bonding Requirements for Telecommunications.

• Care must be taken when running backbone cables to avoid sources of electromagnetic interference or radio-frequency interference.

• No more than two hierarchical levels of cross-connects are allowed, and the topology of backbone cable will be a star topology. (A star topology is one in which all cables lead from their termination points back to a central location.) Each horizontal cross-connect should be connected directly to a main cross-connect or to an intermediate cross-connect that then connects to a main cross-connect. No more than one cross-connect can exist between a main cross-connect and a horizontal cross-connect.

• Equipment connections to the backbone should be made with cable lengths of less than 30 meters (98 feet).

• For high-speed data applications, the total maximum backbone distance should not exceed 90 meters (295 feet) over copper wiring. This distance is for uninterrupted lengths of cable (cross-connects are not allowed).

• Bridge taps or splices are not allowed.

• Multi-pair (greater than four-pair) cable may be used as long as it meets additional performance requirements such as for power-sum crosstalk. These requirements are specified in the Standard.

ANSI/TIA/EIA-568-B recognizes several types of media (cable) for backbone cabling. These media types can be used in combination as required by the installation. The application and the area being served will determine the quantity and number of pairs required. Here are the total cable length allowed between the main cross-connect and the horizontal cross-connect, allowing for one intermediate cross-connect;