The Basics of Structured Cabling
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The Basics of Structured Cabling
A structured cabling system is a complete system of cabling and associated hardware, which provides a comprehensive telecommunications infrastructure. This infrastructure serves a wide range of uses, such as to provide telephone service or transmit data through a computer network. It should not be device dependent.
We further define a structured cabling system in terms of ownership. The structured cabling system begins at the point where the service provider (SP) terminates. This point is the point of demarcation (demarc) or Network Interface Device (NID).
For example, in a telephone system installation, the SP furnishes one or more service lines (per customer requirements). The SP connects the service lines at the point of demarcation.
Every structured cabling system is unique. This is due to variations in:
• The architectural structure of the building, which houses the cabling installation;
• The cable and connection products;
• The function of the cabling installation;
• The types of equipment the cabling installation will support — present and future;
• The configuration of an already installed system (upgrades and retrofits);
• Customer requirements; and
• Manufacturer warranties.
The methods we use to complete and maintain cabling installations are relatively standard. The standardization of these installations is necessary because of the need to ensure acceptable system performance from increasingly complex arrangements.
The U.S. cabling industry accepts the American National Standards Institute (ANSI), in conjunction with TIA/EIA, as the responsible organization for providing and maintaining standards and practices within the profession. It has published a series of standards to design, install, and maintain cabling installations. These help to ensure a proper cabling installation.
The benefits of these standards include:
• Consistency of design and installation;
• Conformance to physical and transmission line requirements;
• A basis for examining a proposed system expansion and other changes; and
• Uniform documentation.
The industry standard term for a network installation that serves a relatively small area (such as a structured cabling installation serving a building) is a local area network (LAN). There are also metropolitan area networks (MANs) and wide area networks (WANs).
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.
The entrance facility includes the cabling components needed to provide a means to connect the outside service facilities to the premises cabling. This can include service entrance pathways, cables, connecting hardware, circuit protection devices, and transition hardware.
An entrance facility houses the transition outside plant cabling to cabling approved for intrabuilding construction. This usually involves transition to fire-rated cable. The entrance facility is also the network demarc between the SP and customer premises cabling (if required). National and regional electrical codes govern placement of electrical protection devices at this point.
The location of the entrance facility depends on the type of facility, route of the outside plant cabling (e.g. buried or aerial), building architecture, and aesthetic considerations. The four principal types of entrance facilities include underground, tunnel, buried, and aerial. (We will cover only aerial entrances in this article.)
In an aerial entrance, the SP cables provide service to a building via an overhead route. Aerial entrances usually provide the lowest installation cost, and they’re readily accessible for maintenance. However, they’re subject to traffic and pedestrian clearances, can damage a building’s exterior, are susceptible to environmental conditions (such wind and ice), and are usually joint-use installations with the power company, CATV company, and telephone or data service providers.
Backbone cabling. 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.
- 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.
Cabling connectors. A connector is a mechanical device you use to interface a cable to a piece of equipment or one cable to another. The role of the connector is to provide a coupling mechanism that keeps loss to a minimum.
In the case of fiber, it allows light impulses to transfer from one connector to another. For copper, it allows electrical signals to transfer from one connector to another.
A good connection requires aligning the connectors, preventing the connectors from unintentional separation, and efficient transferring of light or electricity from one connector to the other.
A connector demonstrates durability by withstanding hundreds of insertion and withdrawal cycles without failing. We calculate this as mean time between failures (MTBF).
Connectors are as essential to the integrity of the entire telecommunications network as is the cable itself. Connectors align, attach, and decouple the media to a transmitter, receiver, another media of same or similar type, an active telecommunications device, or a specified passive telecommunications device.