Structured cabling installations typically include: entrance facilities; vertical and horizontal backbone pathways; vertical and horizontal backbone cables; horizontal pathways; horizontal cables; work area outlets; equipment rooms; telecommunications closets; cross-connect facilities; multi-user telecommunications outlet assemblies (MUTOA); transition points; and consolidation points.
From the entrance facility, the structured cabling network branches out to other buildings, as well as from floor to floor within a building on the backbone cabling system. We use the term backbone to describe the cables handling the major network traffic.
The ANSI/TIA/EIA-568-A standard defines backbone cabling as follows: “The function of the backbone cabling is to provide interconnections between telecommunications closets, equipment rooms, and entrance facilities in the telecommunications cabling system structure. Backbone cabling consists of the backbone cables, intermediate and main cross-connects, mechanical terminations, and patch cords or jumpers used for backbone-to-backbone cross-connection. Backbone cabling also includes cabling between buildings.”
Interbuilding and intrabuilding are two types of backbone cables. Interbuilding backbone cable handles traffic between buildings. Intrabuilding backbone cable handles traffic between closets in a single building.
This standard identifies two levels of backbone cabling. First-level backbone is a cable between a main cross-connect (MC) and intermediate cross-connect (IC) or horizontal cross-connect (HC). Second-level backbone exists between an IC and HC.
The main components of backbone cabling are:
- Cable pathways: shafts, conduits, raceways, and floor penetrations (such as sleeves or slots) that provide routing space for the cables.
- The actual cables: optical fiber, twisted-pair copper, coaxial copper, or some combination of these. (Note: You should avoid areas where potential sources of EMI or electromagnetic interference may exist when planning the routing and support structure for copper cabling.)
- Connecting hardware: connecting blocks, patch panels, interconnections, cross-connections, or some combination of these components, and
- Miscellaneous support facilities: cable support hardware, firestopping and grounding hardware. Note: The terms horizontal and backbone (previously called riser) evolved from the orientations typical for functional cables of these types. However, the physical orientation of the cabling has no bearing on classifying the cable as horizontal or backbone.
The useful life of a backbone cabling system consists of several planned growth periods (typically three to 10 years). This is shorter than the life expectancy of the premises cabling system.