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Fibre Optic Cables - Single-Mode Multi-Mode - Advantages, Construction and Elements

Posted in Network Cabling

Fibre Optic Cables - Single-Mode Multi-Mode - Advantages, Construction and Elements - 4.1 out of 5 based on 9 votes

Fibre Optic Cables - Single-Mode Multi-Mode - Advantages, Construction and ElementsIn this article, we'll talk about Fiber optic cables and how it has changed the design and implementation of network infrastructures, providing high Gigabit speeds, increased security, flexibility and complete immunization from electromagnetic interference.

In the 1950s, more research and development into the transmission of visible images through optical fibers led to some success in the medical world where it was being used in remote illumination and viewing instruments. In 1966 Charles Kao and George Hockham proposed the transmission of information over glass fiber and realized that to make it a practical proposition, much lower losses in the cables were essential.

This was the driving force behind the developments to improve the optical losses in fiber manufacturing and today optical losses are significantly lower than the original target set by Charles Kao and George Hockham.

The Advantages of Using Fiber Optics

Because of the low loss, high bandwidth properties of fiber cables they can be used over greater distances than copper cables. In data networks this can be as much as 2 km without the use of repeaters. Their light weight and small size also make them ideal for applications where running copper cables would be impractical and, by using multiplexers, one fiber could replace hundreds of copper cables. This is pretty impressive for a tiny glass filament, but the real benefit in the data industry is its immunity to Electro Magnetic Interference (EMI), and the fact that glass is not an electrical conductor

Fiber Optic Cable

Figure 1. A Fiber Optic Cable

Because fiber is non-conductive it can be used where electrical isolation is needed, for instance, between buildings where copper cables would require cross bonding to eliminate differences in earth potentials. Fibers also pose no threat in dangerous environments such as chemical plants where a spark could trigger an explosion. Last but not least is the security aspect; it is very, very difficult to tap into a fiber cable to read data signals.

Fiber Construction

There are many different types of fiber cable, but for the purposes of this explanation we will deal with one of the most common types -- 62.5/125 micron loose tube. The numbers represent the diameters of the fiber core and cladding, these are measured in microns which are millionths of a meter.

Construction of Fiber Optic Cable - Components

Figure 2. Construction of Fiber Optic Cable - Components

Loose tube fiber cable can be indoor or outdoor, or both. Outdoor cables usually have the tube filled with gel to act as a moisture barrier to the ingress of water. The number of cores in one cable can be anywhere from 4 to 144.

Over the years a variety of core sizes have been produced but these days there are three main sizes that are used in data communications, these are 50/125, 62.5/125 and 8.3/125. The 50/125 and 62.5/125 micron multi-mode cables are the most widely used in data networks, although recently the 62.5 has become the more popular choice. This is rather unfortunate because the 50/125 has been found to be the better option for Gigabit Ethernet applications.

ST Duplex Patch Lead

Figure 3. ST Duplex Patch Lead

The 8.3/125 micron is a single-mode cable which until now hasn't been widely used in data networking due to the high cost of single mode hardware. Things are beginning to change because the length limits for Gigabit Ethernet over 62.5/125 fiber has been reduced to around 220m and now using 8.3/125 may be the only choice for some campus size networks.

What's the Difference Between Single-Mode and Multi-Mode?

With copper cables larger size means less resistance and therefore more current, but with fiber the opposite is true. To explain this we first need to understand how the light propagates within the fiber core.

Light propagation

Light travels along a fiber cable by a process called 'Total Internal Reflection' (TIR); this is made possible by using two types of glass which have different refractive indexes. The inner core has a high refractive index and the outer cladding has a low index. This is the same principle as the reflection you see when you look into a pond. The water in the pond has a higher refractive index than the air and if you look at it from a shallow angle you will see a reflection of the surrounding area, however, if you look straight down at the water you can see the bottom of the pond


Figure 4. Light transmitted through a Fiber Optic cable

At some specific angle between these two views points the light stops reflecting off the surface of the water and passes through the air/water interface allowing you to see the bottom of the pond. In multi-mode fibers, as the name suggests, there are multiple modes of propagation for the rays of light. These range from low order modes, which take the most direct route straight down the middle, to high order modes, which take the longest route as they bounce from one side to the other all the way down the fiber.

Light bouncing while it travels inside a Fiber Optic cable

Figure 5. Light bouncing while it travels inside a Fiber Optic cable

This has the effect of scattering the signal because the rays from one pulse of light arrive at the far end at different times; this is known as Intermodal Dispersion (sometimes referred to as Differential Mode Delay, DMD). To ease the problem, graded index fibers were developed. Unlike the examples above which have a definite barrier between core and cladding, these have a high refractive index at the centre which gradually reduces to a low refractive index at the circumference. This slows down the lower order modes allowing the rays to arrive at the far end closer together, thereby reducing intermodal dispersion and improving the shape of the signal.

So what about the single-mode fiber?

Well, what's the best way to get rid of Intermodal Dispersion? Easy, only allow one mode of propagation. So a smaller core size means higher bandwidth and greater distances. Simple as that!

 Back to Network Cabling Section

100Base-(T) TX/T4/FX - Ethernet

Posted in Network Cabling

100Base-(T) TX/T4/FX - Ethernet - 4.2 out of 5 based on 15 votes

100Base-(T) TX/T4/FX - EthernetThe 100Base-TX (sometimes referred to 100Base-T) cable was until 2010 perhaps the most popular cable around since it has actually replaced the older 10Base-T and 10Base-2 (Coaxial). The 100Base-TX cable provides fast speeds up to 100Mbits and is more reliable since it uses CAT5e cable (see the CAT 1/2/3/4/5 page).There is also 100Base-T4 and 100Base-FX available, which we discuss at the end of this article.

So what does 100Base-TX/T4/FX mean?

We are going to break the "100Base-T" into three parts so we can make it easier to understand:


The number 100 represents the frequency in MHz (Mega HertZ) for which this cable is made. In this case it is 100 MHz. The greater the MHz, the greater speeds the cable can handle. If you try to use this type of cable for greater frequencies (and, therefore, speeds) it will either not work or become extremely unreliable. The 100 MHz speed translates to 100Mbit per second, which in theory means 12 Mbps. In practice though, you wouldn't get more than 4 Mbps.

10Base-T/2/5/F/35 - Ethernet

Posted in Network Cabling

10Base-T/2/5/F/35 - Ethernet - 3.9 out of 5 based on 8 votes

10Base-T/2/5/F/35 - Ethernet StandardsThe 10Base-T UTP Ethernet and 10Base-2 Coax Ethernet were very popular in the early to mid 1990's when 100 Mbps network cards and hubs/switches were very expensive. Today's prices have dropped so much that most vendors don't focus on the 10Base or 100Base networks but the Gigabit Ethernet networks which also provide backwards support for 100Base-T and 10Base-T standards. Generally speaking, the 10Base-T and 10Base-2 standards are not used anymore today, however having a good understanding on these old standards is still considered valuable.  Finally, we'll also briefly speak about 10Base-5, 10Base-F and 10Base-35 network standards.

So what does 10 BaseT/2/5/F/35 mean?

To make it simpler to distinguish cables they are categorized: that's how we got CAT1, 2, 3, etc. Each category is specific for speed and type of network. But since one type of cable can support various speeds, depending on its quality and wiring, the cables are named using the "BaseT" to show exactly what type of networks the specific cable is made to handle.

We are going to break the "10 Base T" into three parts so we can make it easier to understand:


The number 10 represents the frequency in MHz (Megahertz) for which this cable is made. In this case it is 10 MHz. The greater the MHz, the greater speeds the cable can handle. If you try to use this type of cable for greater frequencies (and, therefore, speeds) then it either will not work or become extremely unreliable. The 10 MHz speed translates to 10Mbit per second, which in theory means 1.2 Mbps. In practice though, you wouldn't get more than 800 kilobits per second (Kbps).

CAT5, CAT5e, CAT6 UTP X-Over / Cross-over Cable

Posted in Network Cabling

CAT5, CAT5e, CAT6 UTP X-Over / Cross-over Cable - 4.1 out of 5 based on 9 votes

The cross-over (or crossover) CAT5 UTP cable has to be one of the most used cables after the classic straight-thru cable. The cross-over cable allows us to connect two computers without needing a hub or switch. If you recall, the hub does the cross-over for you internally, so you only need to use a straight thru cable from the PC to the hub. Since now we don't have a hub, we need to manually do the cross-over.


Why do we need an cross-over cable?

When sending or receiving data between two devices (I.E. computers) one will be sending while the other receives. All this is done via the network cable and if you look at a network cable you will notice that it contains multiple cables. Some of these cables are used to send data, while others are used to receive data and this is exactly what we take into account when creating a crossover cable. We basically connect the TX (transmit) of one end to the RX (receive) of the other!

The diagram below shows this in the simplest way possible:


CAT5 Cross-over

There is only one way to make a CAT5e crossover cable and it's pretty simple. Those who read the "Wiring UTP" article know a crossover cable is a 568A on one end and a 568B on the other. If you haven't read the wiring section, don't worry because we’ll provide enough information to help understand about the concept.

As mentioned previously, the purpose of a crossover cable to connect the transmitting side (TX) from one end, to the Receiving side (RX) at the other end, and vice versa.

Let's now have a look at the pinouts of a typical crossover CAT5e cable:

Straight Thru UTP Cables

Posted in Network Cabling

Straight Thru UTP Cables - 4.0 out of 5 based on 21 votes

UTP Cabling - Straight-thru cable CAT5, CAT5eThis article covers the commonly known Unshielded Twisted Pair (UTP) cable and shows how many pairs the UTP Cat5, Cat5e, Cat6 & Cat7 cables consists of, the colour coding they follow, the different wiring standard that exist (T-568A & T-568B) plus the pin number designations for both standards.

We will be mainly focussing on the wiring of CAT5e & 6 cables as they are the most popluar cables around! We'll also cover wiring classic CAT1 phone cables. It is very important to understand UTP cabling standards and how to correctly terminate them.

Cabling is the foundation for a solid network, and implementing it correctly the first time will help avoid hours of frustration and troubleshooting. On the other hand, if you are dealing with a poorly cabled network, this knowledge will help you to find the problem and fix it more efficiently.

Wiring the UTP cables

We are now going to look at how UTP cables are wired. There are two popular wiring schemes that most people use today: the T-568A and T-568B. These differ only in which color-coded pairs are connected -- pairs 2 and 3 are reversed. Both work equally well, as long as you don't mix them. If you always use only one version, you're okay, but if you mix A and B in a cable run, you will get crossed pairs.

UTP cables are terminated with standard connectors, jacks and punchdowns. The jack/plug is often referred to as a "RJ-45," but that is really a telephone company designation for the "modular eight-pin connector" terminated with the USOC pinout used for telephones. The male connector on the end of a patch cord is called a "plug" and the receptacle on the wall outlet is a "jack."

Cabling - RG-45 Jack and RJ-45 Plug / Connector

Figure 1. A RG-45 Jack and RJ-45 Plug / Connector


As already mentioned, UTP has four twisted pairs of wires. The illustration shows the pairs and the color codes they have. As you can see, the four pairs are labeled:
UTP Colour codes and Pairs

Figure 2. Colour codes & Pairs of UTP CAT 5, CAT 5e, CAT6, CAT7 Cable

Pairs 2 and 3 are used for normal 10/100 Mbps networks, while pairs 1 and 4 are reserved. In Gigabit Ethernet, all four pairs are used.

The picture below shows the end of a CAT5e cable with an RJ-45 connector, commonly used to connect computers to a switch. It also shows a stripped CAT5e cable and identifies the four twisted pairs:


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