Direct Cable Connection

Introduction

From the early PC days, Direct Cable Connection (dcc) was the most popular way to transfer data from one PC to another. Of course, it might seem a bit of an "old fashioned" way to transfer data these days but remember that back then most PC's were running Dos 6.22 or Windows for Workgroups 3.11 if you were lucky !

Today, most computers are equipped with a network card and have an x-over or hub which will allow you to transfer data a lot faster than a serial or parallel cable. But still, there is always a time when you require a simple transfer via serial or parallel and that's what this page is about.

There is a variety of programs which allow you to use the above mentioned cables to successfully transfer data between PCs but you should know that you can achieve your goal without them as well since Windows 95 and above supports the direct cable connection method.

Installing Windows programs or components to transfer data is out of this section's scope, but I have included some notes on what you should check before attempting the Direct Connection via cable, this info is included in the "Important DCC Info". We will also be learning how to create the cables required to meet our goals and comparing the speed of the two (Serial and Parallel)

Because the page ended up being quite long, I decided to split it in order to make it easier to read. Simply click on the subject you'd like to read about:

Serial Direct Connection

Parallel Direct Connection

Source : http://www.firewall.cx/networking-topics/cabling-utp-fibre/122-network-direct-cable-connection.html

Important Direct Cable Connection Notes

Important Points for DCC

This page was designed to provide some notes on Direct Cable Connection (File-transfer) of Win9x/ME/2000 with LAPLINK (Printer port) Cable or Null-Modem (serial port) Cable.

I've successfully used Laplink cable to link two PCs for FILE TRANSFER only (not playing Games), with WIN95 and Direct Cable Connection program using the NetBeui protocol on each computer. You can quickly check to see if the protocol is installed by doubleclicking on the "Network Section" in Control Panel of your Windows operating system.

In addition to the above, you must have installed "Client for Microsoft Networks", "File and Printer Sharing for Microsoft Networks" and optionally the TCP/IP protocol, which will require some configuration. Providing a simply IP Address and subnetmask will be enough for our purposes, the rest of the fields can be ignored. If you would like to allow users to access your files and printer, then ensure both the options in "File and Print Sharing" are selected.

Once you have completed the above steps, you should have the following listed in the "Network Selection" window::

• Client for Microsoft Networks
• TCP/IP
• Netbeui
• File and Printer Sharing for Microsoft Networks

Once your changes are complete, Windows might prompt you to reboot the system, so make sure all work is saved before answering "yes"!

You should also share the Disks on both computers by right-clicking on the selected disks installed in your system and select the "Sharing" option that will appear in the menu. You can access them via your "My Computer" icon on your desktop.

After you complete these actions, you will see a blue hand "holding" your shared drives, indicating that the drive is shared with the rest of the network!


Source : http://www.firewall.cx/networking-topics/cabling-utp-fibre/118-network-direct-cable-notes.html

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

Introduction

The 100Base-TX (sometimes referred to 100Base-T) cable is 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 CAT5 cable (see the CAT 1/2/3/4/5 page).There is also 100Base-T4 and 100Base-FX available, which we discuss later.

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

To make it simpler to distinguish cables they are categorised; that's how we got the CAT1, 2, 3 etc cables. 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 "100Base-T?" into 3 parts so we can make it easier to understand:

100

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 MBytes per second. In practice though, you wouldn't get more than 4 MBytes per second.

Base

The word "Base" refers to Baseband. Baseband is the type of communication used by Ethernet and it means that when a computer is transmitting, it uses all the available bandwith, whereas Broadband (cable modems) shares the bandwidth available. This is the reason cable modem users notice a slowdown in speed when they are connected on a busy node, or when their neighbour is downloading all the time at maximum speed ! Of course with Ethernet you will notice a slowdown in speed but it will be smaller in comparison to broadband.

TX/T4/FX

The "T" refers to "Twisted Pair" physical medium that carries the signal. This shows the structure of the cable and tells us it contains pairs which are twisted. For example, UTP has twisted pairs and this is the cable used in such cases. The 100Base-T is used sometimes to refer to the 100Base-TX cable specification. For more information, see the "UTP -Unshielded Twisted Pair" page where you can find information on pinouts for the cables. All 100Mbit rated cables, except the 100Base-FX, use CAT5 cable.

100Base-TX

The TX (sometimes refered as "T" only) means it's a CAT5 UTP straight through cable using 2 of the 4 available pairs and supports speeds up to 100Mbits. Maximum length is 100 meters and minimum length between nodes is 2.5 meters.

100Base-T4

The T4 means it's a CAT5 UTP straight through cable using all 4 available pairs and supports speeds up to 100Mbits. Maximum length is 100 meters and minimum length between nodes is 2.5 meters.

100Base-FX

The FX means it's a 2 strand fiber cable and supports speeds up to 100Mbits. Maximum length is usually upto 2 kms.

Summary

To summarise, keep the following in mind:

• 100Base-TX/T4 works for 100Mbit networks only and uses unshielded twisted pair cable with RJ-45 connectors at each end
• All CAT5 UTP cables have 4 pairs of cables (8 wires).
• 100Base-TX (sometimes called 100Base-T) uses 2 of the 4 available pairs within the UTP cable, whereas the 100Base-T4 uses all 4 pairs.
• 100Base-FX also works for speeds up to 100Mbits but uses fibre optic cable instead of UTP.

Source : http://www.firewall.cx/networking-topics/cabling-utp-fibre/116-network-cabling-100basetx.html

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

Introduction

The 10Base-T UTP Ethernet and 10Base-2 Coax Ethernet were very popular around the early to mid 1990's when 100Mbit network cards and hubs/switches were very expensive. Today's prices have dropped so much that most vendors don't focus on the 10Base networks but the 100Base ones and, at the same time, support the 10 BaseT and 10Base-2 standard. We will also talk about the 10Base5/F and 35 shortly.

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

To make it simpler to distinguish cables they are categorised; that's how we got the CAT1, 2, 3 etc cables. 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 (and the rest) " into 3 parts so we can make it easier to understand:

10

The number 10 represents the frequency in MHz (Mega HertZ) 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 MBytes per second. In practice though, you wouldn't get more than 800 KBytes per second.

Base

The word "Base" refers to Baseband. Baseband is the type of communication used by Ethernet and it means that when a computer is transmitting, it uses all the available bandwith, whereas Broadband (cable modems) shares the bandwidth available. This is the reason cable modem users notice a slowdown in speed when they are connected on a busy node, or when their neighbour is downloading all the time at maximum speed ! Of course with Ethernet you will notice a slowdown in speed but it will be smaller in comparison to broadband.

T/2/5/F/35

The "T" refers to "Twisted Pair" physical medium that carries the signal. This shows the structure of the cable and tells us it contains pairs which are twisted. For example, UTP has twisted pairs and this is the cable used in such cases. For more information, see the "UTP -Unshielded Twisted Pair" page where you can find information on pinouts for the cables.

10Base-T

A few years ago, the 10 BaseT cables used CAT3 cables, which are used for speeds up to 10Mbit, but today you will find mostly CAT5 cables, which are good for speeds up to 100 Mhz or 100Mbit, these cables are also used for 10Mbit networks. Only 2 pairs of the UTP cable are used with the 10Base-T specification and the maximum length is 100 meters. Minimum length between nodes is 2.5 meters.

10Base-2

This specification uses Coaxial cable which is usually black, sometimes also called "Thinwire coax", "Thin Ethernet" or "RJ-58" cable. Maximum length is 185 meters while the minimum length between nodes is 0.5 meters. 10Base-2 uses BNC connectors which, depending on the configuration, require special terminators. The 10Base-2 specification is analysed here in great detail (also contains pictures) if you wish to read more about it.

10Base-5

This specification uses what's called "Thickwire" coaxial cable, which is usually yellow. The maximum length is 500 meters while the minimum length between nodes is 2.5 meters. Also, special connectors are used to interface to the network card, these are called AUI (Attachment Unit Interface) connectors and are similar to the DB-15 pin connectors most soundcards use for their joystick/MIDI port.

Most networks use UTP cable and RJ-45 connectors or Coaxial cable with BNC "T" connectors, for this reason special devices made their way to the market that allow you to connect an AUI network card to these different cable networks.

The picture below shows you a few of these devices:

10Base-F

This specification uses fibre optic cable. Fibre optic cable is considered to be more secure than UTP or any other type of cabling because it is nearly impossible to tap into. It is also resistant to electro magnetic interference and attenuation. Even though the 10Base-F specification is for speeds up to 10Mbits per second, depending on the type of fibre and equiptment you use, you can get speeds of up to 2Gigabits per second !

10Base-35

The 10Base-35 specification uses broadband coaxial cable. It is able to carry multiple baseband channels for a maximum length of 3,600 meters or 3.6 Kms.

Summary

To summarise, keep the following in mind:

• 10Base-T works for 10Mbit networks only and uses unshielded twisted pair cable with RJ-45 connectors at each end and maximum length of 100 meters. They also only use 2 pairs of cables.
• 10Base-2 works for 10Mbit networks only and uses Coaxial cable. Maximum length is 185 meters and BNC "T" connectors are used to connect to the computers; there are special terminators at each of the coaxial cable.
• 10Base-5 works for 10Mbit networks only and uses Thick Coaxial cable. Maximum length is 500 meters and special "AUI" connectors (DB-15) are used to interface with the network card.
• 10Base-F works for 10Mbit networks only and uses cool fibre optic cable :)

Source : http://www.firewall.cx/networking-topics/cabling-utp-fibre/115-network-cabling-10base-t.html

CAT5 UTP X-Over Cable

Introduction

The cross-over (x-over) CAT5 UTP cable has to be one of the most used cables after the classic straight-thru cable. The x-over cable allows us to connect two computers without needing a hub or switch. If you recall, the hub does the x-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 x-over.

Why do we need an x-over ?

When sending or receiving data between two devices, e.g 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 an x-over 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 X-over

There is only one way to make a CAT5 x-over cable and it's pretty simple. Those who read the "wiring utp" section know an x-over cable is a a 568A on one end and a 568B on the other. If you haven't read the wiring section, don't worry because I'll be giving you enough information to understand what we are talking about.

As mentioned previously, an x-over cable is as simple as connecting the TX from one end to the RX of the other and vice versa.

Let's now have a look at the pinouts of a typical x-over CAT5 cable:

As you can see, only 4 pins are needed for a x-over cable. When you buy a x-over cable, you might find that all 8 pins are used, these cables aren't any different from the above, it's just that there are cables running to the unsed pins. This won't make any difference in performance, but is just a habit some people follow.

Here are the pinouts for a x-over cable which has all 8 pins connected:

Where else can I use a x-over ?

X-over cables are not just used to connect computers, but a variety of other devices. Prime example are switches and hubs. If you have two hubs and you need to connect them, you would usually use the special uplink port which, when activated through a little switch (in most cases), makes that particular port not cross the tx and rx, but leave them as if they where straight through. What happens though if you haven't got any uplink ports or they are already used ?

The X-over cable will allow you to connect them and solve your problem. The diagram below shows a few examples to make it simpler:

As you can see in the above diagram, thanks to the uplink port, there is no need for a x-over cable.

Let's now have have look at how to cope when we don't have an uplink to spare, in which case we must make a x-over cable to connect the two hubs:

All the above should explain a x-over cable, where we use it and why we need it. I thought it would be a good idea to include, as a last picture, the pinouts of a straight thru and a x-over cable so you can compare them side by side:

Straight Thru UTP Cables

Introduction

This article covers the commonly known Unshielded Twisted Pair, UTP, cable and shows how many pairs the UTP Cat5, Cat5e & Cat6 cables consists of, the colour coding they follow, the different wiring standard that exist (T-586A & T-586B) 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! Information on wiring the classic CAT1 phone cables is also included, plus a lot more.

Understanding the correct wiring methods of UTP cables because it's the base of a solid network and will help avoid hours of frustration and troubleshooting if done correctly the first time. On the other hand, if you are dealing with a poorly cabled network, then the information provided here will most likely assist you locating and resolving the problem.

Wiring the UTP cables !

We are now going to look at how UTP cables are wired. There are 2 popular wiring schemes that most people use today: the T-568A and T-568B, that differ only in which color coded pairs are connected - pair 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 OK, 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 an "RJ-45", but that is really a telco designation for the "modular 8 pin connector" terminated with a USOC pinout used for telephones. The male connector on the end of a patchcord is called a "plug" and the receptacle on the wall outlet is a "jack."

As I've already mentioned, UTP has 4 twisted pairs of wires, we'll now look at the pairs to see what colour codes they have:

As you can see in the picture above, the 4 pairs are labeled. Pairs 2 & 3 are used for normal 10/100Mbit networks, while Pairs 1 & 4 are reserved. In Gigabit Ethernet, all 4 pairs are used.

UTP CAT5, 5e & 6 cable is the most common type of UTP around the world ! It's flexible, easy to install and very reliable when wired properly.

        

The left and center pictures show the end of a CAT5 cable with an RJ-45 connector; used by all cables to connect to a hub or to your computer's network card. The picture to the right shows a stripped CAT5 cable, indicating the 4 twisted pairs.

T-568A & T-568B 4-pair Wiring

Ethernet is generally carried in 8-conductor cables with 8-pin modular plugs and jacks. The connector standard is called "RJ-45" and is just like a standard RJ-11 modular telephone connector, except it is a bit wider to carry more pins.

Note: Keep in mind that the wiring schemes we are going to talk about are all for straight through cables only ! Cross over cables are examined on a separate page !

The eight-conductor data cable contains 4 pairs of wires. Each pair consists of a solid colored wire and a white wire with a stripe of the same color. The pairs are twisted together. To maintain reliability on Ethernet, you should not untwist them any more than necessary (like about 1 cm). The pairs designated for 10 and 100 Mbit Ethernet are Orange and Green. The other two pairs, Brown and Blue, can be used for a second Ethernet line or for phone connections.

There are two wiring standards for these cables, called "T568A" (also called "EIA") and "T568B" (also called "AT&T" and "258A"). They differ only in connection sequence - that is, which color is on which pin, not in the definition of what electrical signal is on a particular color.

T-568A is supposed to be the standard for new installations, while T-568B is an acceptable alternative. However, most off-the-shelf data equipment and cables seem to be wired to T568B. T568B is also the AT&T standard. In fact, I have seen very few people using T568A to wire their network. It's important not to mix systems, as both you and your equipment will become hopelessly confused.

Pin Number Designations for T568B

Note that the odd pin numbers are always the white with stripe color (1,3,5,7). The wires connect to RJ-45 8-pin connectors as shown below:

 

Color Codes for T568B 
Pin      Color                   Pair Name 
1    white/orange (pair 2)  TxData + 
2    orange (pair 2)           TxData - 
3    white/green (pair 3)    RecvData+ 
4    blue (pair 1)
5    white/blue (pair 1)
6    green (pair 3)             RecvData- 
7    white/brown (pair 4)
8    brown (pair 4) 

The wall jack may be wired in a different sequence because the wires are often crossed inside the jack. The jack should either come with a wiring diagram or at least designate pin numbers.

Note that the blue pair is on the centre pins; this pair translates to the red/green pair for ordinary telephone lines which is also in the centre pair of an RJ-11. (green=wh/blu; red=blu)

 Pin Number Designations for T568A

The T568A specification reverses the orange and green connections so that pairs 1 and 2 are on the centre 4 pins, which makes it more compatible with the telco voice connections. (Note that in the RJ-11 plug at the top, pairs 1 and 2 are on the centre 4 pins.) T568A goes:

     

Color Codes for T568A 
Pin    Color -                     Pair Name 
1      white/green (pair 3)     RecvData+ 
2      green (pair 3)              RecvData- 
3      white/orange (pair 2)   TxData + 
4      blue (pair 1)
5      white/blue (pair 1)
6      orange (pair 2)            TxData - 
7      white/brown (pair 4)
8      brown (pair 4)

The diagram below shows the 568A and 568B in comparison:

Where are they used ?

The most common application for a straight through cable is a connection between a PC and a hub/switch. In this case the PC is connected directly to the hub/switch which will automatically cross over the cable internaly, using special circuits. In the case of a CAT1 cable, which is usually found in telephone lines, only 2 wires are used, these do not require any special cross over since the phones connect directly to the phone socket.

The picture above shows us a standard CAT5 straight thru cable, used to connect a PC to a HUB. You might get a bit confused because you might expect the TX+ of one side to connect to the TX+ of the other side but this is not the case. When you connect a PC to a HUB, the HUB it will automatically x-over the cable for you by using its internal circuits, this results Pin 1 from the PC (which is TX+) to connect to Pin 1 of the HUB (which connects to RX+).This happens for the rest of the pinouts aswell.

If the HUB didn't x-over the pinouts using its internal circuits (this happens when you use the Uplink port on the hub) then Pin 1 from the PC (which is TX+) would connect to Pin 1 of the HUB (which would be TX+ in this case). So you notice that no matter what we do with the HUB port (uplink or normal), the signals assigned to the 8 Pins on the PC side of things, will always remain the same, the HUB's pinouts though will change depending wether the port is set to normal or uplink.

This pretty much concludes our discussion on straight thru UTP cables !

Source : http://www.firewall.cx/networking-topics/cabling-utp-fibre/113-network-cabling-utp-st.html

Network Cabling

This section talks about the cabling used in today's networks. There's a lot of different type of cabling in today's networks and I am not going to cover all of them, but I will be talking about the most common cables, which include UTP CAT5 straight through and crossover, Coax and a few more.

Cabling is very important if you want a network to work properly with minimum problems and bandwidth losses. There are certain rules which must never be broken when you're trying to design a network, otherwise you'll have problems when computers try to communicate. I have seen sites which suffer from enormous problems because the initial desgin of the network was not done properly !

In the near future, cabling will probably be something old and outdated since wireless communication seems to be gaining more ground, day by day. With that in mind, around 95% of companies still rely on cables, so don't worry about it too much :)

Let's have a quick look at the history of cabling which will allow us to appreciate what we have today !

The Beginning

We tend to think of digital communication as a new idea but in 1844 a man called Samuel Morse sent a message 37 miles from Washington D.C. to Baltimore, using his new invention ‘The Telegraph’. This may seem a far cry from today's computer networks but the principles remain the same. 


Morse code is type of binary system which uses dots and dashes in different sequences to represent letters and numbers. Modern data networks use 1s and 0s to achieve the same result. The big difference is that while the telegraph operators of the mid 19th Century could perhaps transmit 4 or 5 dots and dashes per second, computers now communicate at speeds of up to 1 Giga bit, or to put it another way, 1,000,000,000 separate 1s and 0s every second.

Although the telegraph and the teletypewriter were the forerunners of data communications, it has only been in the last 35 years that things have really started to speed up. This was borne out of the necessity for computers to communicate at ever ncreasing speeds and has driven the development of faster and faster networking equipment, higher and higher specification cables and connecting hardware.

Development of new network technology

Ethernet was developed in the mid 1970's by the Xerox Corporation at its Palo Alto Research Centre (PARC) in California and in 1979 DEC and Intel joined forces with Xerox to standardize the Ethernet system for everyone to use. The first specification by the three companies, called the 'Ethernet Blue Book', was released in 1980, it was also known as the 'DIX standard' after their initials.

It was a 10 Mega bits per second system (10Mbps, = 10 million 1s and 0s per second) and used a large coaxial backbone cable running throughout the building, with smaller coax cables tapped off at 2.5m intervals to connect to the workstations. The large coax, which was usually yellow, became known as 'Thick Ethernet' or 10Base5 - the '10' refers to the speed (10Mbps), the 'Base' because it is a base band system (base band uses all of its bandwidth for each transmission, as opposed to broad band which splits the bandwidth into separate channels to use concurrently) and the '5' is short for the system's maximum cable length, in this case 500m.

The Institute of Electrical and Electronic Engineers (IEEE) released the official Ethernet standard in 1983 called the IEEE 802.3 after the name of the working group responsible for its development and, in 1985, version 2 (IEEE 802.3a) was released. This second version is commonly known as 'Thin Ethernet' or 10Base2; in this case the maximum length is 185m even though the '2' suggest that it should be 200m.

Since 1983, various standard have been introduced because of the increased bandwidth requirements, so far we are up to the Gigabit rate !


Source : http://www.firewall.cx/networking-topics/cabling-utp-fibre.html

Fibre Optic Cables

Introduction

In the 1950's more research and development into the transmission of visible images through optical fibres 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 fibre and realised 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 fibre manufacturing and today optical losses are significantly lower than the original target set by Charles Kao and George Hockham.

The advantages of using fibre optics

Because of the Low loss, high bandwidth properties of fibre cables they can be used over greater distances than copper cables. In data networks this can be as much as 2km 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 multiplexors, one fibre 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.

Because fibre 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. Fibres 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 fibre cable to read the data signals.

Fibre construction

There are many different types of fibre 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 fibre core and cladding, these are measured in microns which are millionths of a metre.

Loose tube fibre cable can be indoor or outdoor, or both, the 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.

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 fibre has been reduced to around 220m and now using 8.3/125 may be the only choice for some campus size networks. Hopefully, this shift to single mode may start to bring the costs down.

What's the difference between single-mode and multi-mode?

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

Light propagation

Light travels along a fibre 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.

At some specific angle between these two view 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 fibres, 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 fibre.

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 fibres 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 fibre?

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 ! :)

Source : http://www.firewall.cx/networking-topics/cabling-utp-fibre/117-network-cabling-fiberoptic.html

Comparing Media Types

Presented in Table 8-1 are comparisons of the features of the common network media. This chart provides an overview of various media that you can use as a reference. The medium is possibly the single most important long-term investment made in a network. The choice of media type will affect the type of NICs installed, the speed of the network, and the capability of the network to meet future needs.

Table 8-1 Media Type Comparison

Media Type	Maximum Segment Length	Speed	Cost	Advantages	Disadvantages
UTP	100 m	10 Mbps to 1000 Mbps	Least expensive	Easy to install; widely available and widely used	Susceptible to interference; can cover only a limited distance
STP	100 m	10 Mbps to 100 Mbps	More expensive than UTP	Reduced crosstalk; more resistant to EMI than Thinnet or UTP	Difficult to work with; can cover only a limited distance
Coaxial	500 m (Thicknet) 185 m (Thinnet)	10 Mbps to 100 Mbps	Relatively inexpensive, but more costly than UTP	Less susceptible to EMI interference than other types of copper media	Difficult to work with (Thicknet); limited bandwidth; limited application (Thinnet); damage to cable can bring down entire network
Fiber-Optic	10 km and farther (single-mode) 2 km and farther (multimode)	100 Mbps to 100 Gbps (single mode) 100 Mbps to 9.92 Gbps (multimode)	Expensive	Cannot be tapped, so security is better; can be used over great distances; is not susceptible to EMI; has a higher data rate than coaxial and twisted-pair cable	Difficult to terminate

Source : http://www.ciscopress.com/articles/article.asp?p=31276&seqNum=4