NETWORK CABLES

INTRODUCTION

Cable is the medium through which information usually moves from one network device to another. Networking cables are used to connect one network device to other network devices or to connect two or more computers to share printer, scanner etc. Different types of network cables like Coaxial cable, Optical fiber cable, Twisted Pair cables are used depending on the network’s topology, protocol and size. The devices can be separated by a few meters (e.g. via Ethernet) or nearly unlimited distances (e.g. via the interconnections of the Internet). Cable is the medium through which information usually moves from one network device to another. There are several types of cable which are commonly used with LANs. In some cases, a network will utilize only one type of cable, other networks will use a variety of cable types. The type of cable chosen for a network is related to the network’s topology, protocol, and size.

While wireless may be the wave of the future, most computer networks today still utilize cables to transfer signals from one point to another.

 

TYPES OF NETWORK CABLES

A) TWISTED PAIR

Twisted pair cabling is a type of wiring in which two conductors of a single circuit are twisted together for the purposes of canceling out electromagnetic interference (EMI) from external sources; for instance, electromagnetic radiation from unshielded twisted pair (UTP) cables, and crosstalk between neighboring pairs. It was invented by Alexander Graham Bell. A cable is often made of several twisted pairs grouped together inside a protective jacket. The twisting eliminates noise (electrical interference) due to adjacent pairs or other sources (motors, relays, transformers).

Twisted pair is therefore suitable for a local network with few nodes, a limited budget and simple connectivity. However, over long distances at high data rates it does not guarantee data integrity (i.e. loss-less data transmission).

 

Advantages

• It is a thin, flexible cable that is easy to string between walls.
• More lines can be run through the same wiring ducts.
• UTP costs less per meter/foot than any other type of LAN cable.
• Electrical noise going into or coming from the cable can be prevented.

 

Disadvantage

Twisted pair’s susceptibility to electromagnetic interference greatly depends on the pair twisting schemes.

 

The two main types of twisted pair cables are:

• Unshielded Twisted Pair (UTP) cables.
• Shielded Twisted Pair (STP) cables.

 

1) Unshielded twisted pair (UTP)

Unshielded twisted pair (UTP) cable is the most popular and is generally the best option for school networks.

The quality of UTP may vary from telephone-grade wire to extremely high-speed cable. The cable has four pairs of wires inside the jacket. Each pair is twisted with a different number of twists per inch to help eliminate interference from adjacent pairs and other electrical devices. The tighter the twisting, the higher the supported transmission rate and the greater the cost per foot.

 

Five categories of UTP cables are:

• Category 1: Traditional telephone cable (voice but no data transmission).
• Category 2: Data transmission up to a maximum of 4 Mbit/s (RNIS). This type of cable contains 4 twisted pairs.
• Category 3: 10 Mbit/s maximum. This type of cable contains 4 twisted pairs and 3 twists per foot.
• Category 4: 16 Mbit/s maximum. This type of cable contains 4 copper twisted pairs.
• Category 5: 100 Mbit/s maximum. This type of cable contains 4 copper twisted pairs.
• Category 5e: 1000 Mbit/s maximum. This type of cable contains 4 copper twisted pairs.

 

2) Shielded Twisted Pair (STP) Cable: Shielded twisted pair contains an aluminum foil shield to avoid interference and are mainly used for backbone networks. Shielded cables can also help to extend the maximum distance of the cables. Shielded twisted pair (STP) is a pair of wires wound around each other and each pair is placed inside a protective foil wrap to protect it from crosstalk. These wires are placed in an outer copper braid to protect it from external interference. STP can use in environment that are near electrical units and radio towers.

Shielded twisted pair cable is available in three different configurations:

• Each pair of wires is individually shielded with foil.
• There is a foil or braid shield inside the jacket covering all wires (as a group).
• There is a shield around each individual pair, as well as around the entire group of wires (referred to as double shield twisted pair).

 

DIFFERENCES BETWEEN UNSHIELDED TWISTED PAIR (UTP) CABLES AND SHIELDED TWISTED PAIR (STP)

Twisted pair cables are widely used in transmitting information, especially across great distances. The twist in the wire cancels out any magnetic interference that may develop in the wiring. There are two common types of twisted pair cabling, STP and UTP. The S stands for Shielded, the U stands for Unshielded, and the TP stands for twisted pair for both. STP simply has additional shielding material that is used to cancel any external interference that may be introduced at any point in the path of the cable. UTP cables have no protection against such interference and its performance is often degraded in its presence. Using STP cables ensure that you get the maximum bandwidth from your cabling even if the external condition is less than ideal.

The biggest drawback to using STP cables is the higher cost. The shielding is an additional material that goes into every meter of the cable, thereby raising its total cost. The shielding also makes the cable heavier and a bit more difficult to bend or manipulate in any way. In terms of usage, UTP is the more prevalent and popular cabling that is used in most homes, offices, and even in large scale businesses due to its lower cost. STP is commonly used by large scale companies in high-end applications that require the maximum bandwidth. STP cables are also used in outdoor environments where the cables are exposed to the elements and manmade structures and equipment that may introduce additional interference. Good examples of this would be the telephone/internet cables that run from your home, to the junction box, down to the establishments of your provider or ISP.

 

 

The differences can be summarized as follows:

• STP cables are shielded while UTP cables are unshielded.
• STP cables are more immune to interference and noise than UTP cables.
• STP cables are better at maximizing bandwidth compared to UTP cables.
• STP cables cost more per meter compared to UTP cables.
• STP cables are heavier per meter compared to UTP cables.

 

 

B) COAXIAL CABLE

Coaxial cable is used as transmission line for radio frequency signals. Its applications include feed-lines connecting radio transmitters and receivers with their antennas, computer network (Internet) connections, and distributing cable television signals. One advantage of coaxial cable over other types of radio transmission line is that in an ideal coaxial cable the electromagnetic field carrying the signal exists only in the space between the inner and outer conductors. This allows coaxial cable runs to be installed next to metal objects such as gutters without the power losses that occur in other types of transmission lines. Coaxial cable also provides protection of the signal from external electromagnetic interference.

Coaxial cable has long been the preferred form of cabling, for the simple reason that it is inexpensive and easily handled (weight, flexibility, .. ).

A coaxial cable is made of up a central copper wire (called a core) surrounded by an insulator, and then a braided metal shield.

 

• The jacket protects the cable from the external environment. It is usually made of rubber (or sometimes Polyvinyl Chloride (PVC) or Teflon).
• The shield (metal envelope) surrounding the cables protects the data transmitted on the medium from interference (also called noise) that could corrupt the data.
• The insulator surrounding the central core is made of a dielectric material that prevents any contact with the shield that could cause electrical interactions (short circuit).
• The core, which actually transports the data, generally consists of a single copper strand or of several braided strands.

 

Coaxial cabling has a single copper conductor at its center. A plastic layer provides insulation between the center conductor and a braided metal shield. The metal shield helps to block any outside interference from fluorescent lights, motors, and other computers.

 

Although coaxial cabling is difficult to install, it is highly resistant to signal interference. In addition, it can support greater cable lengths between network devices than twisted pair cable.

 

Types of coaxial cable

The two different types of coaxial cables are:

• Thinnet.
• Thicknet.

 

1) 10Base2 – thin coaxial cable

Thin coaxial cable is also referred to as Thinnet or CheaperNet.

10Base2 refers to the specifications for thin coaxial cable carrying Ethernet signals. The 2 refers to the approximate maximum segment length being 200 meters. In actual fact the maximum segment length is 185 meters. Thin coaxial cable has been popular in school networks, especially linear bus networks. It is a thin cable (6 mm in diameter), that is white (or grayish) by convention. It is very flexible and can be used in most networks by connecting it directly to the network card. It is able to transport a signal up to around 185 metres without line loss.

It is part of the RG-58 family whose impedance (resistance) is 50 ohms. The different types of thin coaxial cables are differentiated by the central part of the cable (core).

 

Cable and Description 

• RG-58 / U – Central core consisting of a single copper strand.
• RG-58 A/U – Braided.
• RG-58 C/U – Military version of RG-58 A/U.
• RG-59 – Wide band transmission (cable television).
• RG-6 – Thicker diameter, recommended for higher frequencies than RG-59.
• RG-62 – Arcnet Network.

 

2) 10Base5 – thick coaxial cable or Thicknet

Thick coaxial cable is also referred to as Thicknet or Thick Ethernet. 10Base5 refers to the specifications for thick coaxial cable carrying Ethernet signals. The 5 refers to the maximum segment length being 500 meters. Thick coaxial cable has an extra protective plastic cover that helps keep moisture away from the center conductor. It is also called Yellow Cable, because of its yellow color – by convention) is a shielded cable with a thicker diameter (12 mm) and 50 ohm impedance. It was used for a long time in Ethernet networks, which is why it is also known as “Standard Ethernet Cable”. Given that it has a larger-diameter core, it is able to carry signals over long distances: up to 500 meters without line loss (and without signal re-amplification). It has a bandwidth of 10 Mbps and is very often used as a backbone to connect networks whose computers are connected with Thinnet. However, because of its diameter, it is less flexible than Thinnet.

 

Advantages of Coaxial cable

• They are cheap to make.
• They are cheap to install.
• They are easy to modify.
• They have good bandwidth.
• Noise immunity due to low error rate.
• Great Channel Capacity.

 

 

C) FIBER OPTIC CABLE

Fiber optic cabling consists of a center glass core surrounded by several layers of protective materials. It transmits light rather than electronic signals eliminating the problem of electrical interference. It has also made it the standard for connecting networks between buildings, due to its immunity to the effects of moisture and lighting. This makes it ideal for certain environments that contain a large amount of electrical interference.

Fiber optic cables have the ability to transmit signals over much longer distances than coaxial and twisted pair. It also has the capability to carry information at vastly greater speeds. This capacity broadens communication possibilities to include services such as video conferencing and interactive services. The cost of fiber optic cabling is comparable to copper cabling.

The center core of fiber cables is made from glass or plastic fibers. A plastic coating then cushions the fiber center, and Kevlar fibers help to strengthen the cables and prevent breakage. The outer insulating jacket is made of Teflon or PVC.

There are two common types of fiber cables which are single mode and multimode. Multimode cable has a larger diameter; however, both cables provide high bandwidth at high speeds. Single mode can provide more distance, but it is more expensive.

 

Optical fibre is a cable with numerous advantages:

• Light-weight.
• Immune to noise.
• Low attenuation.
• Tolerates data rates on the order of 100Mbps.
• Bandwidth from tens of megahertz to several gigahertz (monomode fibre).

 

Fibre optic cabling is particularly suited to links between distributors (central link between several buildings, known as backbone) as it allows connections over long distances (from several kilometres to 60 km in the case of single-mode fibre) without requiring earthing. Furthermore, this type of cable is very secure as it is extremely difficult to tap in to such a cable.

However, despite its mechanical flexibility, this cable type is not suitable for local network connections as it is difficult to install and is very expensive. For this reason, twisted pair or coaxial cable are preferred for short links.

 

Differences between the Coaxial Cable and Fibre Optics Cable

Coaxial cable is typically a copper core cable with a shield separated by an air gap. It carries electrical signals along the center conductor relative to ground (usually the outer shield is tied to ground.

Fibre optic cable is glass strands which carry light in the form of pulses rather than electrical currents. Fibre carries a digital signal whilst copper (coaxial) commonly carries an analogue signal.

 

GUIDELINES FOR INSTALLING CABLES

• Always use more cable than you need. Leave plenty of slack.
• Test every part of a network as you install it. Even if it is brand new, it may have problems that will be difficult to isolate later.
• Stay at least 3 feet away from fluorescent light boxes and other sources of electrical interference.
• If it is necessary to run cable across the floor, cover the cable with cable protectors.
• Label both ends of each cable.
• Use cable ties (not tape) to keep cables in the same location together.

 

 

D) TELEPHONE CABLE 

Telephone cable generally contains two pairs of wires, for two phone lines. The first pair is green and red; the second is black and yellow. This set of colors is standardized for stranded wires. For solid wires, the colors defined for Ethernet are used; pair 1 is White/Blue + Blue, pair 2 is White/Orange + Orange.