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PTC Building Cable Guide

In any network Data Cabling is involved at some point. It is often the long-lasting component of any network set up. File servers can come and go with new updates of Windows Server, new PCs are constantly being added and a plethora of iPhone and other mobile devices connect via Wi-Fi. All these devices connect at some point over physical cables to the Network. While the cables may remain unchanged for years everything above the physical cable layer may well undergo significant upgrade cycles as routers, switches and sundry other devices are added to the network. These additional devices can add significant traffic and bandwidth requirements to the humble cable network.

In this post we explain the differences in the core components of the physical data cabling that is the bedrock of any network and forms the core of what the industry calls Structure Cabling.

As the capability and traffic requirements of different network sections have changed, so has the physical layer that services them – the data cabling. The many different types of equipment integrated in today’s networks, from printers and workstations to servers and CCTV and the various operating conditions that they have to work in, from quiet office floors to industrial platforms have resulted in many different types of cabling being used often within the same network.

Understanding why these cable types have been developed, how they are used, and what they are used for can be key to making optimum planning and purchase decisions.

While there are dozens of cable types currently in use for data and telecom network cabling, they all fall within three classes, differentiated by the transmission media (the physical material that carries data signals), and by how the transmission medium is shaped.

These three common classes are:

  • Coaxial or Coax cable: Uses single copper wire as the transmission medium
  • Twisted-pair cable: Uses numerous pairs of twisted copper as the transmission medium.
  • Fibre Optic cable: Uses optic fibre rather than copper to carry signals in the form of light rather than electricity.

The material and build determine how much the cable costs, how it’s installed and verified, and many other operational parameters – but it also dictates how it behaves. In particular, it determines:

  • The bandwidth and latency of your network – that is, how much information can be transmitted in a unit of time (megabits or gigabits per second), and how much time it takes for one unit of information to travel over the cable.
  • The distance over which signals of a particular speed can be carried. Electrical signals are inherently attenuated or dampened – and the material used for the cable determines how much a signal attenuates over a given length. As they travel through the cable, data signals are also mixed with interference that cables pick from outside sources and from the electrical installation itself. After a certain point, this interference or noise “drowns out” the useful signal – and the cable material and build determine how long a signal can travel through the wire before so much interference is picked up, that the original signal can no longer be reconstructed
  • Installation requirements: depending on the material and build of the cable, various types of connectors need to be used, installing the cable may require specific precautions (such as protecting cable from the elements) or special operations, such as fusion splicing.

There are several types of cable within each class, and modern company networks routinely use cables from all these three classes.

The most familiar one is twisted-pair cable, which is used on virtually all office floors. Fibre cable is used primarily for long-distance cabling, such as telecom and outdoors security equipment, and for high-bandwidth applications, such as data centre cabling. Coaxial cabling, while rarely used for computer data networking anymore, is used for CCTV, Satellite and radio applications.

Twisted-Pair Cable

twisted par

Twisted-pair cable is the one that most people know as “the network cable”. In fact, there are many different types of twisted-pair cable and choosing the correct one is not always straightforward. It is, however, an important decision, as twisted-pair cable is the fabric of user-facing office network, so it can have a great influence over the efficiency of a company’s daily operation – and form a large percentage of a network’s cabling cost.

Twisted-pair cable gets its name from the fact that it is made of multiple pairs of wires that are twisted around each other. In each of these pairs, one wire carries the signal, and the other one is used as a “ground reference” – that is, one wire “carries” the voltage or signal to be interpreted as a data signal, and the other one is used by the devices at the two ends of the cable in order to agree what zero volts means.

The cables are twisted around each other in order to reduce the influence that outside interference has on the signal. This works because interference is proportional to the surface between the wires, and the best way to keep surface to a minimum is to twist the wires tightly around each other.

In some applications, even this has turned out not to provide enough immunity – so engineers have also added a layer of metallic shielding around the twisted pairs of cabling. This is called Shielded Twisted-Pair cable (STP), in contrast to its unshielded (and, thus, less immune to interference) sibling, Unshielded Twisted-Pair cable (UTP). UTP cable is the one that is most widely used in office floors.

Over the years seven categories of twisted-pair cabling that have been developed, for various applications. By now most of these of these seven categories are only of historical interest and others are used only in very specific niches; the three most important cables are:

  • Cat5e is the one that we know as “Ethernet cable” – and, indeed, is the most common cable used for company data and voice networks. Cat5e cables can carry signals over as much as 100 meters, at speeds of 1 Gbps. The “e” in the name comes from “Extended”: there used to be a “regular” Cat5 standard, but it was deprecated back in 2001; however, the bandwidth and construction requirements between the two are similar, so it is not yet uncommon to see Cat5e cable labelled as Cat5. You will also hear of Cat5e cable being referred to as “RJ-45 cable”. This is not strictly speaking correct – RJ-45 is the type of the connector, the plastic plug with a tiny clip – but RJ-45 is the most common connector used for Cat5e cable.
  • Cat3 (sometimes called station wire or voice-grade wire) was once routinely used for voice networks. Today, new voice installations are built using Cat5e or Cat6 cable, but many voice networks that were built with Cat3 are still around and will be for the foreseeable future.
  • Cat6 cable is an improvement over Cat5e cable, allowing for speeds of to 10 Gbps, and it comes in both shielded and unshielded versions. Cat6 cable can carry 10 Gbps signals over distances up to 55 metres, and 1 Gbps signals over distances up to 100 metres.

How is the right cable choice made? This is a trade-off between three parameters:

  • Bandwidth: 10 Gbps networks inevitably need to use Cat6 cable, but the choices are open below that level, especially when user workstations connect via wireless (and, thus, the connection speed is primarily dictated by the number and speed of the wireless access points).
  • Distance: The distance over which signals have to be transmitted dictates the cable category and shielding choice, as well as the overall network design, as it influences the positioning of switching (and, if needed, repeating) equipment.
  • Cost: Shielded, high-speed cabling costs more than unshielded, low-speed cabling. Finding the set of distance and bandwidth capabilities that serve your business requirements today, and in the foreseeable future, is ultimately the key to choosing the most cost-efficient cabling.

To understand more about network cables read our earlier post entitled Do I need Cat 5E, Cat 6 or Cat 6A?

Fibre Optic Cabling

multi strand fibre optic

Fibre optic cables use a very different transmission principle. A fibre optic cable made of a long strand of glass-like material, called the core, coated by a cover called cladding. The cladding protects the core, but the cladding material is not chosen only for its protective characteristic: one of its properties, called refractive index, is chosen so that, when a light beam traveling through the core hits the cladding under a specific angle, it is reflected almost entirely, with very little of its energy being lost through scattering or refraction.

Thus, as long as we can keep the core thin enough and direct a beam of light well enough as it enters the core, we can carry it over very long distances, with very little degradation. Indeed, some fibre optic cables can carry 10 Gbps signals over distances of up to 10 kilometres.

However, these remarkable capabilities come at a cost: computers, printers and phones use electrical, not optical signals. Somehow, electrical signals need to be converted into light – and then from light back into electrical signals. The transceivers that do this are quite costly; and, compared to copper, so is the fibre itself.

There are two major categories of fibre optic cabling: multimode and singlemode. The “modes” in the name refers, more or less, to the number of paths that rays can take through the core. Multimode cables are thicker and allow multiple propagation paths, which in turn allows for the use of relatively cheap light sources in the transceivers, thus reducing their cost. However, signals attenuate more quickly, and can therefore be transmitted over lower distances. Singlemode fibers only allow one light path, thus minimizing attenuation, but require high-quality light sources and, thus, more expensive transceivers.

Multimode cables – OM1, OM2, OM3 and OM4 – all work at up to 10 Gbps, and OM3/4 also work at 40 Gbps. OM1, OM2 and OM3 are the ones that see most use in small- and medium-sized networks. OM4 is used for high-speed interconnects in data centres and corporate campuses. Singlemode cables – OS1 and OS2 – are primarily used for long-distance, high-speed links. OS1 is meant for indoor use, though, whereas OS2 can be used for outdoors installations as well.

Fibre optic cables have very specific connection and installation requirements. Splicing cables, for example, requires careful aligning of the cores, and certain types of cable, such as OS2, cannot be bent indefinitely. Fibre optic tends to be somewhat more fragile than copper cables but they are lighter.

Usually, fibre optic is what you will want to go with for long-distance deployments. Fibre optic is a very cost-effective solution in these cases and requires a far less complex installation that copper-based deployments. They are also a good option for high-speed core networks, data centre interconnects and for security systems.

Coaxial cable

coaxial-cable-satellite-tv-tv-aerial-2840-p 2

Coaxial cable is rarely seen in compute data networks today, but it is still used for many TV and radio applications, so we will cover it here as well. Coaxial cable uses a central wire strand, called the core, which is coated with an insulating layer, and then with another conductive surface that serves as a ground reference. This second conductor is coated with an insulating material that also provides physical protection.

Coaxial cable has excellent bandwidth (higher, in fact, than twisted-pair cables), but the signal attenuates at a much higher rate. In time, this has limited the use of coax cable to digital telephone networks and TV applications, such as CATV and some older CCTV systems.

Conclusions

Selecting the perfect structured cabling solution for a building can be challenging and is often more complex than the theory prescribes. The results need to balance performance, scalability, cost, durability and extensibility and understand the implications of each on the total cabling design. Experience and past performance also play a considerable part if the final decision. With tens of thousands of kilometres of cables deployed connecting countless devices let PTC assist you with your next build out.

 

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