If you work within a building of even a modest size, chances are that it has a structured cabling system. Structured cabling is not something most people hear about often, but it is vital for the operation of any building network.

In this article, we go over the fundamentals of structured cabling systems. We discuss techniques used to equip a building with networking connectivity throughout, and we also explain the implications of using copper, fiber optics, or both.

How the network reaches your workspace

Service providers for telephony and the internet will connect their infrastructure to the main distribution frame (MDF) of a building. The MDF is essentially a cabling concentrator located in a specialized room on the ground floor or in the basement of a building.

Within each office and workspace, there are typically multiple network jacks to which you can plug in your PC, laptop, printer, IP camera, or other network device to obtain connectivity to both the local network and the internet. You must connect these jacks to the MDF.

But how is this done? What exists between those network jacks and the MDF? How does the network get from the MDF to that plug in your workspace? That's where structured cabling comes in.

Introduction to structured cabling

Structured cabling is a standardized system of interconnected cables, components, and pathways designed to provide network connectivity to all building areas. It does not include any active components, such as routers, switches, firewalls, or other network devices; for this reason, it is often called "passive" infrastructure (as opposed to those active devices).

Once you install structured cabling, it doesn't really do anything (it's passive) until you connect it to some active device.

To understand structured cabling infrastructure and its hierarchical design, let's journey from the network jack to the MDF.

From the network jack to the patch panel

The first leg of our journey goes from the network jack to the patch panel. We've all seen a network jack, so we know what that looks like.

A copper cable is terminated onto that jack. The cable finds its way through various conduits and cable pathways to reach what is known as a telecom closet.

A telecom closet is a small cabinet, closet, or room (depending on size) that contains one or more network racks hosting network equipment. Telecom closets are located throughout a building and act as hubs for the network infrastructure serving the nearby network jacks.

Each telecom closet will typically serve either a whole floor of a building or part of a floor, depending on the size of the building itself.

All the copper cabling coming from the network jacks near the telecom closet is concentrated within the network rack and terminated at one or more patch panels.

Patch panels act as concentrators for the cables that serve the network jacks in the area. A patch panel is simply a strip of network ports that terminate a copper cable in such a way that each port of the patch panel corresponds with a particular network jack.

The patch panel is labeled with codes or numbers on each port corresponding to the numbers or codes on the network jacks. This ensures that each network jack is connected to the correct switch port when activating it.

The patch panel lets network jacks be connected to a switch using a short patch cord from the patch panel port to the appropriate switch port. The following diagram summarizes this connectivity arrangement:

Network jacks and the patch panels serve them are typically on the same building floor. Such cabling is often referred to as "horizontal cabling" because the cable runs are characteristically run in a horizontal fashion on each floor.

Copper cabling

The portion of the structured cabling that connects the network jacks to the local telecom closet uses what we colloquially call Ethernet cabling. Officially, this is called unshielded twisted pair (UTP) cabling.

Although cheap, durable, and easy to install, you can only install UTP cabling with lengths of up to 100 meters from switch to workstation.

Allowing for a patch cord length of up to 5 meters at the patch panel and another 5 meters at the network jack, the cable distance between the patch panel and each network jack must not exceed 90 meters.

This distance limitation plays a major role in determining the locations of telecom closets in relation to the network jacks found within a building.

From the telecom closet to the MDF

The next leg of our journey is from the local telecom closet to the MDF. Once you connect a workstation to the patch panel and switch via the network jack, it has not completed its connectivity journey. This switch in the local telecom closet, which connects end devices such as workstations to the network, is known as an access switch.

This access switch must, in turn, be connected to a distribution switch. A distribution switch is a switch that doesn't connect end devices but rather links together multiple access switches.

The following is a logical diagram of the hierarchical nature of network design:

You can read more about this in our article on Layer 2 and Layer 3 switches.

Fiber optics to the rescue

So, how do we connect our access switches to our distribution switches and our core network? And what if the distance between these locations is more than 100 meters?

In fact, connections between access switches, distribution switches, and the core network will typically exceed 100 meters and will require higher network capacities to be able to handle the aggregate bandwidth from multiple end devices. For this reason, it's typical to use fiber optics for such connections.

Fiber optic cabling can send data over cable lengths reaching hundreds or even thousands of meters and handle higher data throughput.

Connections between telecom closets and the MDF will typically use fiber optic cables, using a structure similar to that of patch panels and UTP cables.

Since we are not connecting end devices but rather one switch in one rack to another switch in another rack, we must use fiber optics from one patch panel to another.

Connections between telecom closets and the MDF typically run from one building floor to another. For this reason, such cabling is often referred to as "vertical cabling" (in contrast to the horizontal cabling mentioned earlier).

Connecting optical patch panels to each other

In this scenario, we have a large patch panel in the distribution telecom closet or MDF, and we have cabling from that one large patch panel connecting to multiple smaller patch panels, with a subset of those cables terminating on each one, like this:

Drawbacks of fiber optics

Although fiber optics can achieve much longer cable lengths and higher speeds than UTP copper cabling, there are some drawbacks that you must consider:

• Fiber optic cabling is much more fragile and requires more specialized equipment and personnel to install.
• It is much more expensive than copper cabling to both purchase and install.
• Fiber optic cables come in several types, including multimode and single mode, depending upon the requirements of the cable run.
• There are a number of different connectors that you can use for fiber optics.

For these reasons, the industry typically uses fiber optic cable only where needed, as described above. When implemented, it is important to ensure that the fiber optic type, connector type, and corresponding patch panels and network equipment are all harmonized and compatible.

Structured cabling summary

The following diagram shows an example of structured cabling as deployed in a building. In it, you can see the workstations, the horizontal and vertical cabling, and the MDF (not labeled) on the ground floor of the building.

Principles and best practices

As a building system, structured cabling is installed for the long term. Properly designed structured cabling installations can last 20 or more years, easily outlasting any active network devices installed on the network.

Once deployed, it is a static and passive structure, with few parts that undergo wear and tear. Once installed, UTP and fiber optic cables do not experience any stress since they are not moved but remain still in their conduits.

Only termination points, network jacks, and patch panel ports may suffer some deterioration, but only if someone connects and disconnects them constantly.

Structured cabling certification

When installing structured cabling, the installer must provide you with a document that certifies the installation. Each individual connection—whether UTP or copper, whether from patch panel to network jack or patch panel to patch panel—must be certified.

This is achieved using specialized equipment that is connected to each end of each terminated cable run. The equipment sends test signals through the cable and returns a printout of the specific measurements that have been taken, including:

• Cable length
• Wire termination order (wire map)
• Attenuation
• Propagation delay
• Crosstalk

These measurements are made and examined against acceptable thresholds. Every terminated cable run should be certified, and only if all circuits pass these tests should the installation be considered complete and the deliverables successfully supplied.

Browse TeleDynamics' website for networking equipment like switches, PoE injectors, and more.

Conclusion

Structured cabling infrastructure is among the unsung heroes of the network world; we hear so little about it because it fails so infrequently. It is almost taken for granted that connectivity is available anywhere there is a network jack, but this dependable access is only possible thanks to the meticulous design, implementation, and management of structured cabling systems.

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