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1. LAN-UTP/FIBER STRUCTURED CABLING

Copper Cabling Systems
Twisted-pair ‘balanced’ copper cable, either unshielded (UTP) or shielded (STP), is the low cost media used as standard for networking a building for all forms of electronic communications to the desktop (for computer, telephone & fax applications).

Telephone Systems / Voice Cabling Installations

Generic voice cabling can also be provided using multi-pair cables connected from the MDF to local DP’s (Distribution Points). Individual user outlets are provided in the work area and terminated with the appropriate connector. Although this method is lower in cost, voice grade cabling does not offer the flexibility to be used as an infrastructure for data communication (computer connection).


Data Cabling Installations
Like computer power and memory, the demand for data transmission capacity and speed has risen exponentially in recent years. Attempting to look ahead and determine with confidence the necessary bandwidth and data rate for the office of the future is becoming more difficult as the pace of changes increases.

The demise of copper in favour of high capacity fibre optic cable has been predicted before, but advanced versions of traditional unshielded twisted pair (UTP) copper cable have so far kept pace with today's information technology. However, building a large network, linking a building to an external data highway or to other buildings, or linking horizontal networks on each floor of a building to a vertical data trunk will almost certainly involve fibre optic cables.

Category Confusion
Currently, as network designers we have three choices: Category 5e (enhanced Category 5), Category 6 copper cabling, or fibre optic to the desktop.

Comparison between CAT5, CAT5e, CAT6, CAT7 Cables

In the context of the 100-ohm UTP (Unshielded Twisted Pair) type of cable used for Ethernet wiring the only categories of interest are Cat3, Cat4, Cat5, Cat5e, Cat6, and Cat7. CATx is an abbreviation for the category number that defines the performance of building telecommunications cabling as outlined by the Electronic Industries Association (EIA) standards. Some specifications for these categories are shown further down.

Up until the late 1980s thick or thin coaxial cable was typically used for 10-Mbps Ethernet networks, but around that time, UTP cabling became more commonly used because it was easier to install and less expensive. UTP CAT3 and CAT4 were used for a quite limited time since the emergence of 100Base-TX networks meant a quick shift to CAT5. By the year 2000, moves to gigabit (1000Base-TX) Ethernet LANs created a need for another specification, CAT5e. CAT5e is now being superseded by CAT6 cable and there is a developing standard for CAT7.

Specifications for Cat3, Cat4, Cat5, Cat5e, Cat6, and Cat7 Cables
Category Type Spectral B/W Length LAN Applications Notes
Cat3 UTP 16 MHz 100m LAN Applications Now mainly for telephone cables
Cat4 UTP 20 MHz 100m 16Mbps Rarely seen
Cat5 UTP 100MHz 100m 100Base-Tx,ATM, CDDI Common for current LANs
Cat5e UTP 100MHz 100m 1000Base-T Common for current LANs
Cat6 UTP 250MHz 100m   Emerging
Cat7 ScTP 600MHz 100m    

It might seem that CAT5 and CAT5e are the same. Pretty much they are, the CAT5e specification simply included some additional limits over the CAT5 specification. The reality is that most CAT5 cable is in fact CAT5e cable just not certified as such. Here is a comparison of those extra specifications.

  CAT5, CAT5e, and CAT6 UTP Solid Cable Specifications Comparison
  Category 5 Category 5e Category 6
Frequency 100 MHz 100 MHz 250 MHz
Attenuation (Min. at 100 MHz) 22 dB 22 dB 19.8 dB
Characteristic Impedance 100 ohms ± 15% 100 ohms ± 15% 100 ohms ± 15%
NEXT (Min. at 100 MHz) 32.3 dB 35.3 dB 44.3 dB
PS-NEXT (Min. at 100 MHz) no specification 32.3 dB 42.3 dB
ELFEXT (Min. at 100 MHz) no specification 23.8 dB 27.8 dB
PS-ELFEXT (Min. at 100 MHz) no specification 20.8 dB 24.8 dB
Return Loss (Min. at 100 MHz) 16.0 dB 20.1 dB 20.1 dB
Delay Skew (Max. per 100 m) no specification 45 ns 45 ns

If you're cabling a mission critical system or you want your network to be future proof, go for the CAT6 cables (and patch panels and connectors), but for the average home or small office network CAT5 or CAT5e will be just fine.

The proposed Category 7 will involve the use of shielded rather than unshielded twisted pair copper cabling. The switch will help achieve data rates of over 1GB. However, it may be that installing fibre is the only way to future-proof an office currently being fitted with a network.

Proponents of fibre to the desktop point out that, despite the advances in signaling technology that have allowed data rates over copper to rise from 10MB to 100MB and now to 1GB, there are intrinsic limitations on the capacity of copper cabling. As data rates begin to approach 10GB, the cost of the transmission equipment will begin to rise rapidly and the transmission distances possible fall equally rapidly. If so, multi-mode fibre optic cables could become more cost effective than copper for horizontal networks.


Structured Cabling Systems
Wherever communications are needed, a cabling infrastructure is required to support it. A Structured Cabling System solution provides all the communications cabling for an entire building in a unified and structured manner, allowing the flexibility for every user to connect to data (computer) and voice (telephone) services or even video (Closed Circuit TV).

One of the key selling points of a structured cabling system is its ability to overcome the problems associated with 'churn rate' which is the average frequency that each person in an office moves location in a year, typically thought to be around 70%. For this reason, buildings are often 'flood wired', whereby more outlets than are initially required are installed, an ideal way of future proofing and allowing for expansion.

Structured (copper) cabling relies on patch panels to feed individual workstations, thus allowing for easy changes in configuration & distribution to be made. Rearrangements are therefore simply catered for at virtually no extra cost.

Cabling is run through each user position and back to the networking rack where the patch panels & network switches are installed. Racks are generally located in a server room or a central communication area.

At the user end, the already laid cables are terminated/impacted in the Information outlets, often termed as RJ45 outlets (similar in appearance to telephone outlets). These outlets are installed or hold firm inside the surface mount boxes with face plates of various shapes & sizes. Similarly at the network rack end, the other ends of the laid cables are terminated in the patch panels.

Each outlet is allocated a unique number that will correspond with an outlet on the patch panel. The Patch cords / Mounting cords can then be run from the outlet to the user device and then 'patched' from the patch panel outlet to the network switch, telephone switch or other electronic equipment


Color Codes
The standards say that Ethernet connectors should be cabled with specific colors on specific pins. There are two standard layouts - if a cable has the same layout on both ends it's a straight through cable. If a cable has one layout on one end and the other layout on the other end then it's a crossover cable. Whilst not universal, the color codes shown below are generally used on professional cables.
 

If a cable has 568A color wiring on both ends then it's a straight through cable.
If a cable has 568B color wiring on both ends then it's also a straight through cable.
If a cable has 568A color wiring on one end and 568B color coded wiring on the other end, then it's a crossover cable.

In fact, while the colors are standardized and usually followed, that's not the important part. What's more important is that one "pair" (wires that are twisted together inside the cable sheath) is used for the transmit side and another pair for the receive side. If pairs aren't used then it's likely your cable will not work. Pairs are identified by the colors. The orange wire and the orange with white stripe (or sometimes white with orange stripe) wire are a pair. The brown wire and the brown with white stripe wire are a pair. Etc.

 
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Fibre Optic Cabling - HISTORY
In 1870, John Tyndall demonstrated that light follows the curve of a stream of water pouring from a container, it was this simple principle that led to the study and development of applications for this phenomenon. John Logie Baird patented a method of transmitting light in a glass rod for use in an early colour TV, but the optical losses inherent in the materials at the time made it impractical to use. 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, as they began using them in remote illumination and viewing instruments. In 1966 Charles Kao and George Hockham proposed the transmission of information over glass fibre, and they also 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 out by Charles Kao and George Hockham.

Fibre Optics Advantages
Because of the Low loss, high bandwidth properties of fibre cable 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 multiplexers, one fibre could replace hundreds of copper cables. This is pretty impressive for a tiny glass filament, but the real benefits in the data industry are 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 which stops 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 only 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, this was 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.
 
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Fibre Optics Disadvantages
In order to present a balanced picture, it is important that we also look at the drawbacks of using fibre optics.

Specialist skills needed: Specialist skills are required for the installation of fibre optics, especially in the terminating and testing phase. BP Communications Ltd are specialist in this field and have Engineers trained with the specialist skills required.

Cost of installation: Although prices are reducing all the time for much of the equipment, the cost are still higher than for copper cabling installations.

Cost of transmission equipment: The cost of converting an electrical signal into an optical signal for transmission down a fibre, and the added cost of converting it back into an electrical signal is much more expensive than sending an electrical signal down a copper cable.


Fibres cannot carry power:
Electrical power cannot be carried along a fibre. This has important implications for fibre to the subscriber , where at the moment the electricity needed to make the telephone work is provided down the wire from the exchange. 

Vulnerable: Because of the enormous information carrying capacity of fibre, there is a tendency to ‘put all your eggs in one basket’. This means that a fibre fault can result in catastrophic loss of communications. Fibres are often though of as being very fragile, however they are in fact surprisingly strong, particularly under tension.

Myths and disinformation: For some people, fibre optics is still viewed as a black art. At BP Comms, we aim to remove the myths and provide real independent, accurate information.

Termination methods
The termination of Fibre can be carried out by using following two methods:

1.   Direct Termination (Connectorisation)
2.    Fusion Splicing (Permanent Connection)

Fibre to fibre interconnection can consist of a splice (permanent connection) or a connector which differs from the splice in its ability to be disconnected and reconnected. Fibre optic connector types are as various as the applications for which they were developed. Different connector types have different characteristics, different advantages and disadvantages, and different performance parameters. But all connector have the same four basic components:

The Ferrule: The fibre is mounted in a long, thin cylinder, the ferrule, which acts as a fibre alignment mechanism. The ferrule is bored through the centre at a diameter that is slightly larger than the diameter of the fibre cladding. The end of the fibre is located at the end of the ferrule. Ferrules are typically made of metal or ceramic, but they may also be constructed of plastic. 

Also called the connector housing, the connector body holds the ferrule. It is usually constructed of metal or plastic and includes one or more assembled pieces which hold the fibre in place. The details of these connector body assemblies vary among connectors, but bonding and/or crimping is commonly used to attach strength members and cable jackets to the connector body. The ferrule extends past the connector body to slip into the coupling device.

The Cable: The cable is attached to the connector body. It acts as the point of entry for the fibre. Typically, a strain-relief boot is added over the junction between the cable and the connector body, providing extra strength to the junction.

The Coupling Device: Most fibre optic connectors do not use the male-female configuration common to electronic connectors. Instead, a coupling device such as an alignment sleeve is used to mate the connectors. Similar devices may be installed in fibre optic transmitters and receivers to allow these devices to be mated via a connector. These devices are also known as feed-through bulkhead adapters.

Direct Termination
There are a number of techniques which may be used to terminate a fibre into a connector:

Epoxy and Polish Termination Method: In this method the fibre is glued into the ferrule using a heat curing epoxy, excess fibre is scribed off and then the remaining fibre and any epoxy is polished off to leave a mirror finish. This technique of termination is often used for Multimode and Singlemode Fibre.

This is a well established and proven technique & provides good performance and long term reliability but the termination cycle of this technique is lengthy & moreover the power is also required for curing the oven. Also the skill level required for this is fairly high.

Light Crimp Termination Method: The ‘Crimp, Cleave & Polish’ connectors are required for this technique. They eliminate the use of conventional epoxy and only require one grade of Polishing film. The connectors have pre-loaded ‘dry’ adhesive and excess fibre is cleaved off close to the end face using a special tool, so only minimal polishing is required.

This technique is used where the quick terminations are required and performance is not too critical. The benefit of this method is that the terminations can be done quickly, No curing oven and hence No power is required. For this technique the special crimp tool and cleaving tools are required because of high tolerance & precise ferruling. Since a good quality ceramic ferrule is incorporated hence the connector used is also fairly expensive.

In case the connectors are fitted with a pre-polished ferrule then the polishing operation is not be done, thus reducing the termination time even further.

Hot-melt Termination Method: A product originally launched in the UK by 3M in 1992. Utilises a special type of epoxy pre-loaded into the connector. The epoxy needs to be softened by heating before the fibre can be inserted.

This technique of termination is used for Data Communication. The benefit of this method is the Quick termination time & no epoxy to mess around with. On the contrary the special curing oven and tooling is required and also the prepared fibre has to be inserted into hot connector .

Adhesives Termination Method: This type of technique relies on the bonding between two different chemicals to secure the fibre in the ferrule. One chemical (adhesive) is pre-loaded into the connector, the other (activator) is applied to the fibre which is then entered into the ferrule and bonding takes place.

This technique of termination is used for Data Communication. The benefit of this method is the faster fitting time with no need for lengthy curing process and also provides good performance with long term reliability. On the contrary the termination cycle is lengthy & the power is also required for curing the oven. Also the skill level required for this is fairly high.

Fusion Splicing
An alternative to the direct termination of optical fibres is to splice on pre-connectorised pigtails.

Pre-connectorised pigtails are manufactured in a factory under controlled conditions where good return loss performance can be achieved. This performance is often required in systems where lazers are used as the light source.

Fusion Splicer

Fusion splicing, if performed correctly will provide the lowest loss when compared to other splicing methods. The process of performing a fusion splice involves applying a focussed heat source that will fuse the two fibres together. For this action, a piece of equipment known as a Fusion Splicer is used.

In the Fusion Splicer the two pieces of fibre are lined up in such a manner that the two cores are aligned, or on the x-y-z axis and then a current is passed between two electrodes and the glass is literally welded together. The completed splices are protected by a plastic splice sleeve which is shrunk onto the fibre using an integrated oven on the splicing unit. Each ‘spliced’ fibre is then inserted into a splice tray for storage.


The Benefits & the Drawbacks of Fusion splicing over conventional Connectorisation
  Benefits:
 
The Engineers or the installation teams do not require the connectorisaton skills or tooling. 
All connector types may be handled in the same manner 
Quality of terminations is guaranteed. 
Connectors may be fitted in a clean environment and hence the performance of connectors are likely to be better  
 
Drawbacks - Splices require protection in some form of enclosure
  Drawbacks:
 
The need to buy or hire expensive fusion splice equipment or investment in mechanical splicing.
Additional splice losses can get introduced.
Splices require protection in some form of enclosure

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