Basic Requirements for Backbone Cabling

Backbone cabling includes:

• Cabling between equipment rooms and building entrance facilities
• In a campus environment, cabling between buildings' entrance facilities
• Vertical connections between floors

ANSI/TIA-568-C.1 specifies additional design requirements for backbone cabling, some of which carry certain stipulations, as follows:

• Grounding should meet the requirements as defined in J-STD-607-A, the Commercial Building Grounding and Bonding Requirements for Telecommunications.
• The pathways and spaces to support backbone cabling shall be designed and installed in accordance with the requirements of TIA-569-B. Care must be taken when running backbone cables to avoid sources of EMI or radio frequency interference.
• No more than two hierarchical levels of cross-connects are allowed, and the topology of backbone cable will be a hierarchical star topology. (A hierarchical 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. Figure 1 shows multiple levels of equipment rooms and telecommunications rooms.
  
   
  Figure 1: Star topology of equipment room and telecommunication rooms connected via backbone cabling
• Centralized optical fiber cabling is designed as an alternative to the optical cross-connection located in the telecommunications room or telecommunications enclosure when deploying recognized optical fiber to the work area from a centralized cross-connect. 
• The length of the cord used to connect telecommunications equipment directly to the main or intermediate cross-connect should not exceed 30 meters (98′).
• Unlike horizontal cabling, backbone cabling lengths are dependent on the application and on the specific media chosen. (See ANSI/TIA-568-C.0 Annex D.) For optical fiber, this can be as high as 10,000 meters depending on the application! However, distances of ≤ 550 meters are more likely inside a building. This distance is for uninterrupted lengths of cable between the main cross-connect and intermediate or horizontal cross-connect.
• Bridge taps or splices are not allowed.
• Cables with more than four pairs may be used as long as they meet additional performance requirements such as for power-sum crosstalk. These requirements are specified in the standard. Currently, only Category 5e cables are allowed to have more than four pairs.