What is Structured Cabling for LANs (Local Area Networks)?

By Colin Yao

What is structured cabling?

Modern computer LAN (local area network) wiring has the concept of structured cabling.

With today's high speed networks, people realize that the networking system must be broken up into shorter chunks that allow workstation wiring to be concentrated, with each cable length short enough to support the high data rate.

Based on aforementioned reasons, structured wiring standard has been developed to help define a computer wiring system that stays within the maximum wiring distance for various LAN topologies. For example, the horizontal cable wiring length is 100 meters for 100BaseT networks.

What do we do to observe the 100 meters wiring standard?

In order to achieve the wiring concentration standard, telecommunication rooms (wiring centers) are placed at planned locations in a building. These telecom rooms are then interconnected to provide the total network connectivity for the building.

This can be explained in a three stories building. At one same corner of each floor, a telecom rooms is constructed; these telecom rooms are then connected by backbone wiring (cables run vertically through the floors and link all telecom rooms together).

On each floor, a telecom room concentrates all workstation cables for that floor. Each workstation has a wall mounted jack. The network cable is terminated at that jack and runs directly to the telecom room. The cable may run in wire trays or conduit, or be draped over supports such as a drop ceiling. For larger floors, more than one telecom room may be needed.

Horizontal Cabling

The horizontal wires, which run from workstations on the same floor to the telecom room, are then terminated on punchdown termination, or directly onto a patch panel. The punchdown terminations or patch panels could be rack mounted (19" or 23" racks), cabinet mounted or wall mounted.

In the telecom room, network equipment such as a hub or switch is connected to each station cable, which electrically terminates the cable run. The hub or switch then passes the computer signal on to other work stations or servers, or even to other telecom rooms for ultimate connectivity with the entire network.

Vertical Cabling (Backbone Cabling)

Telecom rooms on each floor are then connected together by backbone cabling (also called vertical cabling for floor to floor connections). These backbone cablings typically are done from floor to floor to floor.

Usually telecom rooms should be located directly above one another in order to minimize the cable runs length, but this also varies from building to building.

With the emerge of Gigabit Ethernet and 10 Gigabit Ethernet, fiber optic cable is the most appropriate choice for backbone cabling since they provide much higher bandwidth than traditional Cat5, Cat6 or even Cat7 twisted pair copper cables. Another advantage of fiber is that fibers can run much longer distance than copper cable, which makes them especially attractive for backbone cabling.

The difference between backbone cabling and horizontal cabling

Since backbone cabling typically passes through from floor to floor, the cables used for backbone cabling have very different requirement than the horizontal cablings.

1. Fire ratings. Backbone cables must have standard imposed fire rating specifications. Typically this is OFNR (Optical Fiber Non-Conductive Riser) rated. If the backbone cable passes through plenum area (spaces in the building used for air return in air conditioning), the cable must be OFNP (Optical Fiber Non-conductive Plenum) rated.

2. Physical securing. Physical securing for vertical riser cables is also different than horizontal cables. So is the cable strength, since vertical riser cables need to have enough strength to support its own weight.

Colin Yao is an expert on fiber optic networking technologies and products. Learn more about apc pigtail, fiber optic pigtails, fiber pigtails on Fiber Optics For Sale Co. web site.

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