.::: G R A N D D O M A I N . C O M :::.

Cable Testing Solutions

granddomain — Mon, 10 Dec 2007 08:22:18 GMT

CABLE TESTING

ACR
The first thing to understand about testing data cables is the ACR, this stands for Attenuation to Crosstalk Ratio. The pink area in the graph is the attenuation, this can be caused by several things as will be explained below, and the blue area is the crosstalk. Attenuation is the reduction in signal strength over the length of the cable and frequency range, the crosstalk is the external noise that is introduced into the cable. So, if the two areas meet, the data signal will be lost because the crosstalk noise will be at the same level as the attenuated signal.

ACR is the most important result when testing a link because it represents the overall performance of the cable.

So what causes the signal to attenuate?, and where does the crosstalk come from?
Below are of some of the terms used in high performance cable testing, and a description of what they mean.

Length
The length of a cable is one of the more obvious causes of attenuation because the longer it is, the more resistance it has, and therefore less of the signal will get through. To measure the length, a cable tester uses Time Domain Reflectometry (TDR). A pulse is sent down the cable and when it reaches the far end it reflects back, by measuring the time it takes to travel down the cable and back again, the tester can determine how long the cable is. To do this, the tester also needs to know how fast the pulsed signal is travelling, this is called the Nominal Velocity of Propagation (NVP) and is expressed as a percentage of the speed of light. The NVP is usually somewhere between 60% and 90% of the speed of light, with most Cat 5E cables being around 70%. Due to the twists in the cable, the measured length will be greater than the physical length, so if a run looks like it might be over 80m it would be wise to check it before it is tied up and terminated.

Wire Map
This test is to ensure that the two ends have been terminated pin for pin, i.e. that pin 1 at the patch panel goes to pin 1 at the outlet, pin 2 goes to pin 2 etc. etc. The wire map also checks for continuity, shorts, crossed pairs, reversed pairs and split pairs. A Split pair is probably the only thing that requires an explanation here, as they are undetectable with a simple continuity tester, this is because pin for pin they seem to be correct. As explained on the Cabling Basics page, balanced line operation requires that the signal is transmitted over a pair of wires that are twisted together, with a 'split pair' the signal would be split between two different pairs.

Return Loss
When a cable is manufactured there are slight imperfections in the copper. These imperfections all contribute to the Structural Return Loss (SRL) measurement because each one causes an impedance mismatch which adds to the cables attenuation.

DC loop resistance
This is simply the resistance between the two conductors of a twisted pair which is looped back at the far end. The primary purpose of this test is to make sure that there are no high resistance connections in the link.

Attenuation
This is the decrease in signal strength (expressed as negative dB) from one end of a cable to the other. The main causes of attenuation are impedance,
temperature, skin effect and dielectric loss. Impedance is the combination of resistance, inductance and capacitance in a cable, it is measured in Ohms and opposes the flow of current. Skin effect is phenomena which happens at high frequencies where the signal tries to escape from the confines of the copper and into the air. The signal travels along the outer 'skin' of the copper which effectively reduces the cross sectional area of the cable and therefore increases its resistance.

NEXT
This stands for Near End cross Talk, and it occurs because alternating current flow produces an electromagnetic field around the cable, this field then induces a current flow in adjacent cables. The strength of this field increases with the frequency of the signal, and because the speed of data transmissions is ever increasing, NEXT is a big problem.

The name 'Cross Talk' comes from the telecommunications industry, you may have heard a faint conversation in the background while on the phone yourself, this is caused by the electromagnetic effect between adjacent telephone wires. In the transmission of data, cross talk is at its highest level in the RJ45 connection as it enters the cable, or at the 'Near End'. The term 'Near End' is slightly confusing because data can travel in both directions, and the NEXT test is carried out in both directions automatically by the tester, so the NEXT result is relative to the end of the cable that it was carried out on.
The twists in a cable help to cancel out the effects of NEXT and the more twists there are, the better the cancellation, however, the twists also increase attenuation, so there is a trade off between NEXT cancellation and attenuation. The twist rates in data cables are optimised for the best overall performance, the twist rates are also varied for each pair within the cable to help combat crosstalk.

PSNEXT
This stands for Power Sum Near End Cross Talk and is actually just a calculation. When a tester carries out the NEXT test it measures the cross talk on each pair as affected by each of the other three pairs individually, PSNEXT is simply the addition of the three NEXT results for each pair. So this is the combined effect that a pair would be subject to when used in a network that supports a four pair transmissions method, e.g.. Gigabit Ethernet.

FEXT, ELFEXT and PSELFEXT
Basically, Far End Cross Talk (FEXT) is like NEXT but it is measured at the far end (well that seems logical!). However, on its own FEXT doesn't mean much because the length of the cable determines how much the signal is attenuated before it can affect the pairs at the far end. To compensate for this, and to provide a more meaningful result, the attenuation is subtracted from the FEXT test and the result is then called Equal Level Far End Cross Talk (ELFEXT).
And of course, no test parameter these days would be complete without adding the results together for each pair and calling it a Power Sum measurement, so now we have Power Sum Equal Level Far End Cross Talk or PSELFEXT for short.

Delay
This is the propagation delay or the time it takes for the signal to travel from one end of the cable to the other, it is not very important on it own because it value is directly proportional to the length of the cable. What is important is the relationship between the delays on each of the four pairs. This brings us nicely on to .........................

Delay Skew
Now this is important, Delay Skew is the difference between the fastest and slowest pairs. Some networks use a four pair transmission method, this means that the signal is split into four, sent down the four pairs in the cable and re-combined at the far end. It is essential that the signals reach the far end at near enough the same time, otherwise the signal will not be re-combined correctly.

FUSION SPLICING

granddomain — Mon, 10 Dec 2007 08:07:34 GMT

FUSION SPLICING

Fusion Splicing

There are several reasons for splicing a fiber cable, these include:

To join two fibers due to a breakage.

To connect some of the cores straight through a patch cabinet.

To extend a cable run.

To reduce losses, a fusion splice has much lower losses than two connectorized cables joined through a coupler.

Or to attach a pre-terminated pigtail.

A Pigtail is a short length of fiber with a factory fitted and polished connector. In the past these were used in preference to field terminations because of the complexities at the time of manually terminating optical fibers. These days pigtails are mainly used where the environment isn't suitable for manual terminations or where speed is a factor.

As with all fiber termination methods, safety is very important so first some safety tips.

* Always work in a clean and tidy area.

* Fiber offcuts are hard to see and can easily penetrate the skin especially if they get into your clothes, so care must be taken to ensure the safe disposal of all offcuts. Dispose of fiber scraps immediately using a suitable container and do not throw into a waste paper bin. * Because of the dangers of ingesting a fiber, do not eat or drink in the termination area.

* Fusion splicers use an electric arc to fuse the fibers together so they should never be used in an environment where flammable gases or liquids are present.* Never look into the end of a live fiber connector. Holding some multimode fibers up to a piece of paper may prove the presence of light and therefore prove that it is live, but it doesn't prove that it isn't live! Some laser powered equipment use light which is outside of the visible spectrum, so err on the side of caution.

Overview

A fusion splice is a way of joining two fiber cores by melting the ends together using an electric arc. A splicing machine is used because an extremely high degree of accuracy is needed, the machine first has to align the cores and then apply the exact amount of heat to melt the ends before pressing them together.

Splicing can be carried out using a mechanical splice but these only hold the fiber ends together, precisely aligned but not permanently joined.

There are four basic steps to fusion splicing

1 - Strip back all coatings down to the bare fibers and clean using isopropyl alcohol.
2 - Cleave the fibers using a precision cleaving tool and put the heat shrink tube on to one of the ends.
3 - Fuse the fibers together in the fusion splicer.
4 - Put the heat shrink protector on the fiber joint.

Fusion Splicing Method

Stripping

Strip back the external sheathing of the cable using a rotary stripping tool.Cut back the aramid strength member using ceramic or kevlar scissors.

Strip the primary buffer from the fiber using fiber strippers not ordinary wire strippers. Do this a small section at a time to prevent the fiber breaking, about 10mm (3/8 in) on each cut is fine until you get used to it. Strip back about 35mm (1.5 in).

Clean the bare fiber with a lint free wipe and isopropyl alcohol, it will "squeak" when it is clean.

Cleaving

The cleaver first scores the fiber and then pulls the fiber apart to make a clean break. It is important that the the ends are smooth and perpendicular to get a good joint, this is why a hand held cleaver will not do.

Cleavers vary from manufacturer to manufacturer and you should read the instructions for the one you are using. Basically the operation consists of putting the fiber into the groove and clamping, then close the lid and press the lever. Easy eh!
Good cleaving tools can cost between $800 to $3000

The Fusion Process

Once the fiber ends are prepared they are placed in the fusion splicer. Press the button and the machine takes care of the rest of the fusion process automatically.

First the two fibers are aligned, you can see this on the photo where a much magnified image shows the two fiber ends. The display also shows how well the cleaver does its job of producing a perfect 90 degree cut.

If you watch very carefully in the video you can see the X and Y alignment that takes place. The splicer aligns the fibers on one axis and then from another camera angle set at at 90 degrees, it aligns the other axis. This high precision alignment is critical for a low loss joint, any mismatch of the fiber cores will significantly reduce the propagation of light through the joint.

Bearing in mind that we are dealing with two very small glass rods of only 125 microns in diameter, it brings it home as to how extremely accurate these machines are.

Once the fibers are aligned the splicer fires an electric arc between the two ends which melts them immediately and pushes them together, or fuses them into one piece of fiber.

The fusion splicer then tests for dB loss and tensile strength before giving the "OK" beeps for you to remove the splice from the machine.

Protection

The splicer in the video has a built in heat shrink oven, so when the fiber is taken out of the machine the protective tube is slid into place and the whole assembly is put into the oven to shrink the tube on to the splice. The protective tube gives physical protection to the splice and further protection is provided by placing the splice into a splice tray.

Once all of the fibers have been joined the whole tray is then fixed into a splice box which protects the cable joint as a whole and the cable clamps are then tightened to prevent any external forces from pulling on the splices.

Fusion splicers are expensive and can cost between about $5,000 to over $30,000, so you need to be doing a lot of splicing to justify the initial outlay but, for a low loss and relatively fast connection it is the only tool for the job.

Fiber Optic - Cold Cure Termination

granddomain — Mon, 10 Dec 2007 08:05:38 GMT

Cold Cure Termination

There are several different methods of terminating fiber cables including heat-cured, cold cured, pre-injected epoxy, UV adhesives and crimped termination's. There are also environmental conditions to take into consideration, but for the purpose of this tutorial we will discuss the cold cure method as it is the most widely used system and probably the easiest to learn. It is also preferable on site as it doesn't require a power source for ovens and fusion splicers.

As with all fiber termination methods, safety is very important so first some safety tips.

* Always work in a clean and tidy area.

* Fiber offcuts are hard to see and can easily penetrate the skin especially if they get into your clothes, so care must be taken to ensure the safe disposal of all offcuts. Dispose of fiber scraps immediately using a suitable container and do not throw into a waste paper bin.

* Because of the dangers of ingesting a fiber, do not eat or drink in the termination area.

* Observe manufacturers recommendations when using solvent based adhesives.

* Never look into the end of a live fiber connector. Holding some multimode fibers up to a piece of paper may prove the presence of light and therefore prove that it is live, but it doesn't prove that it isn't live! Some laser powered equipment use light which is outside of the visible spectrum, so err on the side of caution.

On to the lesson . . . . . .

The Connector

	There are three parts to a fiber connector (four if you count the dust cap) they are: The connector housing, the connector body and the strain relief boot. The body contains the ferrule which aligns the fiber perfectly for mating with another
connector, it's a precision engineered component. The housing contains the fiber body and provides the latching mechanism. The strain relief boot prevents the fiber from bending past the critical point at which it can break.

Preparation

Fill the syringe with adhesive ready to use. Strip back the external sheathing of the cable using a rotary stripping tool. Cut back the aramid strength member using ceramic or kevlar scissors. Slide the strain relief boot onto the fiber to be terminated. Strip the primary buffer from the fiber using fiber strippers not ordinary wire strippers.
Do this a small section at a time to prevent the fiber breaking, about 10mm (3/8 in) on each cut is fine until you get used to it. Strip back about 30mm (1.25 in).

"Sticking" on the connector!

Inject the adhesive into the connector body until a small bead appears at the end of the ferrule.

Clean the bare fiber with a lint free wipe and isopropyl alcohol, it will "squeak" when it is clean.

Apply the primer to the bare fiber either with the brush supplied or by dipping it into the bottle.

Push the fiber in to the connector body in one smooth action until you feel the buffer reach the back of the ferrule.

The chemical reaction between the adhesive and the primer happens almost instantly so don't stop while inserting the fiber otherwise it will stick before it is fully home.

Cleaving

The purpose of cleaving the fiber is to ensure that it breaks cleanly at 90 degrees, although you may think that because it is ground down to the ferrule and then polished it wouldn't make any difference if it were just snapped off! It makes a big difference. If the fiber shatters or splinters down past the ferrule then no amount of polishing will turn it into a good connection. A hand held scribe or pen cleaver is adequate for this job, unlike fusion splicing where a perfectly cleaved end is essential for a good connection.

Lightly scribe the fiber as close to the ferrule as possible and use a slight tug to break the fiber end away. Dispose of the fiber offcut immediately in the hazardous debris container.

Polishing

The first step in polishing is to take the fiber down to the ferrule, for this we use about a 9 micron lapping film. Hold the connector in one hand and rub the nub of fiber down to the ferrule with the lapping film. When it is close enough you will feel it get smoother.

Step two. Insert the connector into the polishing puck, this keeps it perpendicular to the polishing surface. Place a sheet of 2 micron lapping film on a suitable flat surface.

Hold the connector and puck, and place it on the polishing surface. Then move it in a figure of 8 pattern about 30 times using slight pressure. The end is now polished and can be inspected with the microscope. Some people recommend 3 or 4 stages of polishing but we find that we get just as good results from just these two grades of abrasives.

Visual Check

Using the illuminated microscope check that the polished end is OK. Things to look out for are excessive scratches or remnants of the epoxy adhesive. You can now fit the housing and dust cap.

Testing

Once both ends are terminated the fiber can be tested. Fiber testing used to involve a bulky OTDR (Optical Time Domain Reflectometer) operated by a geek with a degree in optical physics, but these days a simple hand held light source and power meter can be used. To give it a full test you can also use a fiber certification tools which simply tells you what systems the fiber is good for. These simple to use (but quite expensive) instruments will give a print out of all test parameters and losses as well as the communications media it will work on.

FIBER OPTIC Introduction

granddomain — Mon, 10 Dec 2007 07:49:18 GMT

Fiber Optic Introduction

The installation and termination of optical fibers used to be regarded as somewhat of a 'Black Art' but with standardization and easier terminating techniques this is no longer true. A basic knowledge of the subject, together with a quick lesson and some practice can get you started in fibre optics, but to really understand the subject and gain full in-depth knowledge will require some formal training.

There are lots of Fibre Optic training companies offering recognised qualifications and a quick search on the net should find one in your area.

If you are in the UK, Optical Technology Training Ltd offer several different courses to choose from including a City & Guilds qualification.

There are also hundreds of books on fibre optics and a search on the Barnes and Noble web site will find nearly 600 titles. Without reviewing them all it is difficult to know what to recommend, but two of the best sellers in this category seem to follow on quite nicely from this page without getting too involved with mathematics. The two books are the Introduction to Fibre-Optics by John Crisp and Understanding Fiber Optics, Third Edition by Jeff Hecht.

Right, lets get on with the lesson

First a bit 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.

The advantages of using fibre optics
Because of the Low loss, high bandwidth properties of fiber 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 multiplexors 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 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 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 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. 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.

How TOKEN RING Works

granddomain — Mon, 10 Dec 2007 07:45:44 GMT

Unlike Ethernet, Token Ring uses a ring topology whereby the data is sent from one machine to the next and so on around the ring until it ends up back where it started. It also uses a token passing protocol which means that a machine can only use the network when it has control of the Token, this ensures that there are no collisions because only one machine can use the network at any given time.

The Basics
Here is an animated GIF that shows the basic operation of a Token Ring, and below is an explanation of what is going on.

Although 16Mbps is the standard ring speed these days (and Fast Token Ring is being developed) we will consider a 4Mbps Token Ring in this tutorial to explain the basic concepts.

Hit 'Refresh' on your browser to start the animation from the beginning

At the start, a free Token is circulating on the ring, this is a data frame which to all intents and purposes is an empty vessel for transporting data. To use the network, a machine first has to capture the free Token and replace the data with its own message.

In the example above, machine 1 wants to send some data to machine 4, so it first has to capture the free Token. It then writes its data and the recipient's address onto the Token (represented by the yellow flashing screen).

The packet of data is then sent to machine 2 who reads the address, realizes it is not its own, so passes it on to machine 3. Machine 3 does the same and passes the Token on to machine 4.

This time it is the correct address and so number 4 reads the message (represented by the yellow flashing screen). It cannot, however, release a free Token on to the ring, it must first send the message back to number 1 with an acknowledgement to say that it has received the data (represented by the purple flashing screen).

The receipt is then sent to machine 5 who checks the address, realizes that it is not its own and so forwards it on to the next machine in the ring, number 6.

Machine 6 does the same and forwards the data to number 1, who sent the original message.

Machine 1 recognizes the address, reads the acknowledgement from number 4 (represented by the purple flashing screen) and then releases the free Token back on to the ring ready for the next machine to use.

That's the basics of Token Ring and it shows how data is sent, received and acknowledged, but Token Ring also has a built in management and recovery system which makes it very fault tolerant. Below is a brief outline of Token Ring's self maintenance system.

Token Ring Self Maintenance
When a Token Ring network starts up, the machines all take part in a negotiation to decide who will control the ring, or become the 'Active Monitor' to give it its proper title. This is won by the machine with the highest MAC address who is participating in the contention procedure, and all other machines become 'Standby Monitors'.

The job of the Active Monitor is to make sure that none of the machines are causing problems on the network, and to re-establish the ring after a break or an error has occurred. The Active Monitor performs Ring Polling every seven seconds and ring purges when there appears to be a problem. The ring polling allows all machines on the network to find out who is participating in the ring and to learn the address of their Nearest Active Upstream Neighbour (NAUN). Ring purges reset the ring after an interruption or loss of data is reported.

Each machine knows the address of its Nearest Active Upstream Neighbour. This is an important function in a Token Ring as it updates the information required to re-establish itself when machines enter or leave the ring.

When a machine enters the ring it performs a lobe test to verify that its own connection is working properly, if it passes, it sends a voltage to the hub which operates a relay to insert it into the ring.

If a problem occurs anywhere on the ring, the machine that is immediately after the fault will cease to receive signals. If this situation continues for a short period of time it initiates a recovery procedure which assumes that its NAUN is at fault, the outcome of this procedure either removes its neighbour from the ring or it removes itself.

Token Ring Operation using a Hub

A Token Ring hub simply changes the topology from a physical ring to a star wired ring. The Token still circulates around the network and is still controlled in the same manner, however, using a hub or a switch greatly improves reliability because the hub can automatically bypass any ports that are disconnected or have a cabling fault.

Further advancements have been made in recent years with regard to Token Ring technology, such as early Token release and Token Ring switching but as this site is primarily concerned with cabling issues we will not go into any more detail here.

How Ethernet Works

granddomain — Mon, 10 Dec 2007 07:43:31 GMT

Ethernet was developed in the late 1970's by the Xerox Corporation at their Palo Alto Research Centre in California. It has been estimated that over 70% of the worlds networks use the Ethernet protocol, so with this in mind it would seem only sensible to discuss how it works. If you would like to buy books on this subject, have a look at the Computers section of Barnes and Nobles online book store.

OK, lets begin the lesson. Ethernet uses a protocol called CSMA/CD, this stands for Carrier Sense, Multiple Access with Collision Detection. To understand what this means lets separate the three parts.

Carrier Sense - When a device connected to an Ethernet network wants to send data it first checks to make sure it has a carrier on which to send its data (usually a piece of copper cable connected to a hub or another machine).

Multiple Access - This means that all machines on the network are free to use the network whenever they like so long as no one else is transmitting.

Collision Detection - A means of ensuring that when two machines start to transmit data simultaneously, that the resultant corrupted data is discarded, and re-transmissions are generated at differing time intervals.

Here are some animated GIF's to help explain basic Ethernet operation, below each one is a description of what is happening.
If you want to start an animation from the beginning hit your browsers refresh button.

The Basic Ethernet Bus

This is a coax based Ethernet network where all machines are daisy chained using RG58 coaxial cable (sometime referred to as Thin Ethernet or Thin-net).

Machine 2 wants to send a message to machine 4, but first it 'listens' to make sure no one else is using the network.

If it is all clear it starts to transmit its data on to the network (represented by the yellow flashing screens). Each packet of data contains the destination address, the senders address, and of course the data to be transmitted.

The signal moves down the cable and is received by every machine on the network but because it is only addressed to number 4, the other machines ignore it.

Machine 4 then sends a message back to number 2 acknowledging receipt of the data (represented by the purple flashing screens).

But what happens when two machines try to transmit at the same time? …… a collision occurs, and each machine has to 'back off' for a random period of time before re-trying.

For the sake of simplicity I have omitted the acknowledgement transmissions from the rest of the animation's on this page.

Collisions

This animation starts with machine 2 and machine 5 both trying to transmit simultaneously.

The resulting collision destroys both signals and each machine knows this has happened because they do not 'hear' their own transmission within a given period of time (this time period is the propagation delay and is equivalent to the time it takes for a signal to travel to the furthest part of the network and back again).

Both machines then wait for a random period of time before re-trying. On small networks this all happens so quickly that it is virtually unnoticeable, however, as more and more machines are added to a network the number of collisions rises dramatically and eventually results in slow network response. Time to buy a switch!!!

The exact number of machines that a single Ethernet segment can handle depends upon the applications being used, but it is generally considered that between 40 and 70 users are the limit before network speed is compromised.

Using a Hub

An Ethernet hub changes the topology from a 'bus' to a 'star wired bus', here's how it works.

Again, machine 1 is transmitting data to machine 4, but this time the signal travels in and out of the hub to each of the other machines.

As you can see, it is still possible for collisions to occur but hubs have the advantage of centralised wiring, and they can automatically bypass any ports that are disconnected or have a cabling fault. This makes the network much more fault tolerant than a coax based system where disconnecting a single connection will bring the whole network down.

Using a Switch

To overcome the problem of collisions and other effects on network speed, a switch is used.

With a switch, machines can transmit simultaneously, in this case 1 & 5 first, and then 2 & 4. As you can see, the switch reads the destination addresses and 'switches' the signals directly to the recipients without broadcasting to all of the machines on the network.

This 'point to point' switching alleviates the problems associated with collisions and considerably improves network speed.

In the real world however, one or more of these machines will be servers, and as most network traffic is between the clients and a server a serious bottle neck can occur. The answer to this problem is to make server connections faster than the clients. The normal solution is to have the client machines on 100Mbs ports and the servers on 1000Mbs ports (Gigabit Ethernet). This ten to one ratio is usually adequate because not all of the clients will need to access the servers at the same time.

FAULT Findings on Structured Cabling Systems

granddomain — Mon, 10 Dec 2007 07:40:18 GMT

First the Basics
I've lost track of the number of times I've been on a customers site and found that they have re-used the old Cat 3 and Cat 4 patch leads simply because they didn't have any Cat 5 leads at the time. These leads almost never get changed because it hasn't made any noticeable difference to the operation of the network. Years later of course, things start to go wrong and the old leads aren't even suspected because "they've not been a problem in the past".

By all means use old leads on voice systems but never use them on data networks.

It is like throwing a load of rocks into a smooth running stream, the data will probably still get through at first but when you increase 'the flow', they will start to impede the throughput.

If the problem only affects one PC, take that PC to the patch cabinet and plug it directly into the hub. This may seem like an obvious thing to try but it has to be said as it proves whether the fault is actually a cabling problem or not. You should use a known good port on the hub and a known good patch lead, if the machine works then the problem is either the original hub port, the patch lead, the drop lead or the fixed cabling. From here it is easy to eliminate each part of the link, but it must be carried out methodically, one component at a time. Another point worth mentioning is that a patch lead that works fine in a Token Ring network may not work in an Ethernet network, this is because they use different pins on the RJ45 plug. Token Ring uses pins 3, 4, 5 & 6 whereas 10BaseT Ethernet uses 1, 2, 3 & 6, so any cable with a fault on pins 1 & 2 will work for Token Ring but not for Ethernet. Although a Cat 5/5E tester can be very expensive, you can buy a simple continuity tester for under $100 which will test for shorts, opens and crossed pairs, this will not prove your cabling is up to standard but they are quick and easy for finding faulty Cat 5 patch leads.

Another thing to watch out for is the wiring configuration, there are actually two different schemes allowed under the 568A standard. These are called 258A (or T568B), and 258B (or T568A). Pin for pin they are the same but with the orange and blue pairs swapped over, so as long as you have the same type of jack at each end, no problem. However, if you have 258A on one end, and 258B on the other then you have a crossed pair.

Check the time of day!
The time of day may indicate another cause of network problems. If the problem only occurs at a certain time, it maybe that the network is slowing due to an increase in traffic say at 9:00am or 5:00pm. If, for instance, the drawing office starts at 9:00am and twenty draughtsmen are all trying to pull large drawing files from a server which is on the general network, this will impact the rest of the company's business. Likewise at 5:00pm when they are all saving their work back to the server the sudden increase in traffic may cause so many collisions that the network to grinds to a halt. A process of elimination is easy to implement and if this is the cause, it is time to put the drawing office and the CAD server on to its own hub or switch.

Electrically 'noisy' environments
Another common cause is electromagnetic interference from electric motors and sources of high frequency radio waves. The more obvious things to look for are cable routes that pass too close to lift motors, arc and spot welders, heavy plant machinery which use large electric motors, and fluorescent light fittings. All of these things, if situated close to the data cabling, could induce spikes into the network. Take a walk around the building and make a note of all possible causes, and then try to eliminate them one at a time.

What next?
Eliminating possible causes one at a time is the ideal, but sometimes the problem occurs so infrequently that it is almost impossible to track down, and specialist equipment and engineers have to be employed. 'Network Sniffers' and mains monitors can be hired from companies such as Livingston Hire, and if you are confident that you can correctly interpret the results, do it yourself. If not, well its the end of the line and time to call in the specialists.

To summarize, the following considerations should be taken into account:

1. Low grade patch leads and/or drop leads.

2. Time of day.

3. Increase in network traffic from other sources.

4. Electromagnetic interference.

If you need more in-depth information on any IT related subject check out the wealth of knowledge at www.SearchNetworking.com. They have news, advice and tips on all aspects of computer networking, and is a valuable source of help for network managers and administrators .

Ethernet
Most of the points mentioned above should find Ethernet problems, however, there are a couple of things that should be taken into consideration when dealing with Gigabit Ethernet.

Although Gigabit Ethernet was designed to run on 100MHz cable, problems may arise with older Cat 5 systems. The more stringent Cat 5E standards take into consideration that Gigabit Ethernet uses a four pair transmission method, but this was not part of the test parameters with Cat 5. If you are trying to run Gigabit Ethernet over standard Cat 5 cabling, then the whole system should be tested to confirm that it meets the new Cat 5E standard.

It used to be said that multimode fibre was good for 2km, but recently it has been found that for Gigabit Ethernet applications the length limit is right down to around 220m over 62.5/125 fibre. The only way to prove if a fibre is good enough for Gigabit Ethernet is to use a certification tool. These are fairly expensive test instruments, but you should be able to hire one from a specialist hire company. The results give a clear 'pass or fail' for different applications, but bear in mind that one dirty connector can affect the results considerably.

Token Ring
Type 1 cable was designed for Token Ring and is a very robust system, however, some of the data connector termination's I've seen leave a lot to be desired. It is possible to re-terminate these connectors, so if you have some that are looking decidedly worn or broken, get them fixed. Because of their large size, data connectors tend to get knocked and bumped and this can be the cause of a lot of problems. Also remember that Type 1 is a shielded system which has to be grounded properly at the patch cabinet, ground continuity should also be carried right through to the PC. Failure to ensure proper grounding can cause a multitude of problems.

The data connector was designed to 'loop back' when unplugged to ensure that if the main ring cabling is interrupted the network will stay up. If you look into the end of a data connector you will see two gold strips one behind the other These 'short circuit' the transmit and receive pairs when the connector is unplugged, and loops the signal back the other way thereby maintaining ring integrity. This very clever piece of design does have a slight draw back in that a disconnection on the main ring path can go unnoticed because the data connector is doing its job. This means that if you have a fault on the ring and it is already working on loop back, you will only know when a second fault occurs. In theory, if your Token Ring is working perfectly and the ring is complete, you should be able to disconnect the main ring path anywhere without disrupting the network. If, on the other hand, your Token Ring is already running on loop back due to a fault that you are not aware of, disconnecting the main ring will effectively split the network in half.

AS400 cabling
AS400e series have three new features which are designed to speed up throughput to 5250 devices, unfortunately some Twinax hardware will not support them.

Split Mode
When operating in Split mode, the AS400 poles its ports two at a time, i.e. 0 & 4, 1 & 5, etc., this only causes a problem when eight port multiplexors are used as they will be trying to multiplex and de-multiplex both simultaneous signals. To overcome this, two four port mux's should be used, or the Split mode feature turned off.

Optimized Mode
In optimized mode no overheads are added to the data frame which under normal conditions works fine, however some star hubs and mux's need the additional information to work correctly. The solutions are to either buy new hubs and mux's, or again turn off the Optimized mode feature on the AS400.

Express Mode
This is simply the AS400 running at 2Mbs instead of 1Mbs, and again some hubs and mux's can't handle this speed. The solution?, same as above really, buy new hubs or switch off the Express mode feature.

Length limits
The maximum distance for Twinax cable on each port of the Work Station Controller is 1800m, this limit is reduced to 1458m when running in Express mode. It is also a little known fact that there is a minimum length limit of 25 feet or about 8m on all types of cable used to transmit 5250 signals. This distance is the length of the signal itself, and if the cable is less than this, the signal can become corrupted by its own reflections before it has finished transmitting.

When using IBM Type 1 cabling, the limits are the same as Twinax operation (1800m) but this reduced to 1312m when running in Express mode.

For UTP installations the distances vary according to whether Twinax is used on part of the installation. The limits range from a maximum of 364m when only a few metres of Twinax has been used between the Work Station Controller and the hub, down to a minimum of only 36m where more than 1600m of Twinax has been used. For further information visit the IBM networking web site.

Where fibre is used between mux's or converters, the maximum limit is 2400m, again this may be reduced if the AS400 is running in Express mode.

5250 Star hubs
Some active star hubs can introduce delays into the system, if these delays are close to the limits for 5250 operation, it can affect the reliability and performance of the network. Passive star hubs don't cause delays, so if you are having intermittent problems with a particular line it might be worth trying a passive star in place of an active one. This is sometimes the case when a line of terminals has been working perfectly well on the old Twinax but problems start to arise when they are moved to the new structured cabling.

When running 5250 devices over a UTP structured cabling system problems can sometimes be due to mismatched baluns. Make sure all of the baluns on each line are from the same manufacturer, and that they are wired for the same pin-out configuration, some star hubs use pins 1 & 2 as the active pins and some use 4 & 5.

RS232
With RS232, transmit and receive are connected via pins 2 and 3 of the D type plugs with pin 7 (on 25 way) being the ground point. The other pins are used to control the flow of data, usually referred to as 'hard wired handshaking', the pin-out chart below shows what each pin is used for.

A device can be either a Data Terminal Equipment (DTE) or a Data Communications Equipment (DCE), this determines whether pin 2 is transmit and pin 3 receive or vice versa. Usually you will find that terminals are DTE and printers are DCE and the ports on the server board will be configured to communicate with one or the other. This makes a big difference if you start moving things around and inadvertently connect terminals or printers into the wrong ports.

25 pin	9 pin	Abbreviation	Description
1	N/A	GND	Shield Ground
2	3	TXD	Transmit Data
3	2	RXD	Receive Data
4	7	RTS	Request to Send
5	8	CTS	Clear to Send
6	6	DSR	Data Set Ready
7	5	GND	System Ground
8	1	CD	Carrier Detect
9	N/A	0	Reserved
10	N/A	0	Reserved
11	N/A	STF	Select Transmit Channel
12	N/A	SCD	Secondary Carrier Detect
13	N/A	SCTS	Secondary Clear to Send
14	N/A	STXD	Secondary Transmit Data
15	N/A	TCK	Transmission Signal Element Timing
16	N/A	SRXD	Secondary Receive Data
17	N/A	RCK	Receiver Signal Element Timing
18	N/A	LL	Local Loop Control
19	N/A	SRTS	Secondary Request to Send
20	4	DTR	Data Terminal Ready
21	N/A	RL	Remote Loop Control
22	9	RI	Ring Indicator
23	N/A	DSR	Data Signal Rate Selector
24	N/A	XCK	Transmit Signal Element Timing
25	N/A	TI	Test Indicator

Introduction to Structured Cabling

granddomain — Mon, 10 Dec 2007 07:38:03 GMT

There are also lots of books on the subject of cabling and a selection of these can be found at the Barnes and Noble website in their Computers section, although my personal favourite is The Cabling Handbook 2nd Edition by John Vacca. It has over 1300 pages covering all aspects of network cabling and includes chapters on The Standards, Network Design, Wireless Communications, Fibre and Home Wiring, plus a whole lot more.

If you don't want to invest any money on training until you are seeing some financial results, then you can gain valuable experience by actually doing some work for an existing cabling company.

Here are some basic questions you may be asking yourself if you have never installed a structured cabling system before.

What are 'The standards' ?
There are three main cabling standards:

EIA/TIA 568A - This is the American standard and was the first to be published (1991).
ISO/IEC 11801 - The International standard for structured cabling systems.
CENELEC EN 50173 - The European cabling standard (the British version is BS EN 50173).

The reason for having a 'Standard' is to define a method of connecting all types of vendors voice and data equipment, over a cabling system that uses a common media, common connectors and a common topology. This means that a building can be cabled for all its communications needs without the planner or architect ever having to know what type of equipment will be used.

It is advisable to get a copy of one of the cabling standards documents, although once you have read through it once and understood some of what it describes, it will probably be filed away and never opened again. If you have ever tried to read a standards document you will know that it is hard work. Trying to separate the useful information from all the technical jargon can be very time consuming and even then you may not find the answer to your question. The bad news is, the Cabling Standards are no different, they are full of cross references, formulas and tables all of which can be a very daunting prospect and can make the installation engineer think twice about installing the stuff.

Now for the good news, the standards are mostly concerned with the performance criteria of the components of a cabling system, and, as that is guaranteed by the manufacturers of the different cabling components, you don't have to worry about it. Great eh!

What type of cable do I install?
Please go to the Questions and Opinions page for my personal views on the subject.

What materials do I need?
Lets work on a hypothetical installation. It is for 30 double outlets, in one building, with an average run of about 30m. Each double outlet will be used for one PC and one telephone. A detailed breakdown of this list giving reasons for sizes and quantities is Here

1 x 27U, 600 x 600 cabinet.
3 x 32 way RJ45 patch panels.
6 x boxes of Cat 5e cable.
30 x double Cat 5e outlets and backboxes
30 x PBX master telephone adapters
30 x 1.5m patch leads
30 x 2m patch leads
30 x 3m fly leads.
Trunking, cable ties and a method of labelling the system.

How do I install it?
Here are the basic do's and don'ts.

Although the maximum cable length for a Cat 5e/6/7 system is often reported to be 100m, this length is inclusive of patch and drop leads. Cable testers however, when set to perform a 'Basic Link' test, take this into account and you will find that the maximum length is set to either 90m or 94m depending on the standard you are testing to. Also, because the length is measured with a Cable Analyser it is not the physical length of the run but the copper length that is measured. The copper length is longer due to the twists in the cable pairs, so if a run looks like it might be over 85m it would be wise to check it before it is tied up and terminated.

Each outlet cable should be run directly back to the patch cabinet, that is one cable per outlet. A transition point or connection box is allowed if necessary, but in practice this can be more trouble than its worth.

Care should be taken when pulling cables in to ensure that they are not kinked or nicked.

Cable routes should be planned to avoid fluorescent light fittings and power cables (exceptions can be made in the case of optical fibre). They should not be run in the same conduit as power, or the same channel of a trunking system, and where they are run parallel to power they must be at least 60mm apart (BS7671-92) . Crossing power cables is allowed but it must be at right angles, and some form of bridge should be used.

A means of supporting the cables should be installed such as cable tray, catenary wire or cable tie fixings, tying cables to ceiling hangers is not permitted. Cables should be tied at a minimum of 500mm intervals on horizontal runs and more frequently on vertical runs, with no more than 48 cables in a loom. Cable ties should only be finger tight to avoid crushing the cables as this could affect the cables performance characteristics. Do not use cable tie guns or staple guns.

Cable trays should be used under false floors, if not, a suitable method of keeping the cable off the floor slab should be employed. This is because the lime in the concrete apparently reacts with the cables sheathing, and over time could damage the cable. I personally think the cable will have outlived its usefulness long before this could have any affect on the cables performance.

Care should be taken when pulling cables into trunking to avoid damage due to snagging. Trunking partitions should be used to separate the data cables from power, and bridges should be used where data cables have to cross the mains.

When terminating patch panels, cable looms should not exceed 48 cables. Each cable loom should then be tied in a tidy manner to a cable tray fitted the full length of the cabinet.

All terminating should be carried out according to the manufacturers instructions and guidelines, and the standards for generic cabling systems. The cable sheath should be stripped back no more than 13mm from the point of termination and the twist rates should be maintained.

Cable ties MUST be fitted to the individual RJ45 modules in the patch panels and outlets to support each cable.

When terminating outlets, care must be taken to avoid damaging the copper cores when stripping back the outer sheathing.

Excessive amounts of cable should not be left in the outlet backbox. Care should be taken when attaching the outlet faceplate not to kink, trap or strain the cable.

Cable tray should be fitted in cabinets housing structured cabling to keep cable looms secure and tidy, and to provide room for any additional cabling.

All cabinets must be earthed to the 16th edition IEEE wiring regulations (British regulations). Where shielded cable is used the earth should be clean and where two cabinets are linked with a copper backbone (shielded or unshielded) a minimum of 10mm² earth wire should also be installed to cross bond the cabinets.

Testing and documentation
All testing whether copper or fibre should begin with calibration of test equipment, and batteries should be fully charged before testing begins. Descriptions of the various test parameters can be found on the Cable Testing page.

On all installations, and particularly on large jobs, two way radios or internal telephone lines should be used to ensure correct numbering of outlets and patch panels during testing.

What do they mean by Balanced line? How does it work?
Balanced line operation is a transmission method which helps to eliminate the effects of noise on the cable. In the first diagram a coaxial cable is transmitting a 4V signal, this is unbalanced as all of the 4V signal is carried by the centre core of the coax with respect to the grounded screen. If 1V of noise is introduced, it adds to the signal being transmitted making 5V, this could interfere with our data.

With a balanced line transmission our 4V signal is split into +2V and -2V on one twisted pair, so we still have 4V between the two. Now when we introduce the 1V of noise, the +2V becomes +3V, and the -2V becomes -1V, but the potential difference between the two is still 4V. The devices we put on the ends of the cable to make the line balanced are called baluns, this name is derived from the function of the devices of converting between balanced and unbalanced transmission modes.

These days, more and more equipment is being designed to operate on balanced lines without the need for baluns, but there are still a lot of older systems out there that still use these converters.

MHz? Mbps? Baud?
If you are confused about the different terms used in data communications this article written by Mark Barratt should help to clear things up.

Bandwidth is the difference between the highest and lowest frequencies which will propagate through an equipment or system. In many cases, the lower limit is DC, zero hertz, and so the bandwidth is the same as the upper frequency limit. The public telephone system constrains all signals to the range 300 Hz - 3 kHz. Its bandwidth is therefore 2.7kHz.

In the most obvious method of modulation (representing data electrically), two different voltages are used to represent a '1' and a '0'. The receiver expects a data bit at a certain time, and samples the input voltage to determine the value of the bit. This is called "amplitude shift keying" (ASK). The maximum frequency of the signal will depend upon the slew rate (the time taken to change from 0 to 1, or vice versa). The maximum slew rate is the upper frequency limit, and the slew rate, in turn, limits the maximum data rate.

Plainly, the bandwidth of such a system directly limits the data rate, but in theory it need not. Consider a protocol which uses "frequency shift keying" instead. Here, two different frequencies (both of them within the legal bandwidth) are used to represent 1 and 0. The maximum data rate is now the maximum speed at which you can shift between the two frequencies. This is still limited by the bandwidth, but not so directly - the resulting maximum data rate is higher. And what happens if you use more than two frequencies? You can then transmit more than one bit of information per signal transition, upping the data rate again without increasing the maximum frequency of the signal.

It is techniques such as these which have allowed the development of 56k modems. Using a combination of multiple-level amplitude, frequency and phase modulation, they manage to extract up to 56,000 bits per second of performance from the aforementioned 2.7 kHz bandwidth. To achieve this using plain 2-level ASK would require a bandwidth of hundreds of kilohertz.

"Baud rate", strictly, is a measure of "signal elements" per second, and is not a useful measure where the above signalling techniques are being used. Such systems are generally rated in "bits per second" bps. It is worth noting that manufacturers will claim the highest figure they can for this parameter, so that the figure will include bits which are part of the signalling protocol rather than the user's data, and may even incorporate an assumption about the compressibility of the data. It is rarely (if ever) valid to divide bps by 8 to arrive at bytes of data transmitted/expected per second.

Structured Cabling Overview

granddomain — Mon, 10 Dec 2007 07:34:30 GMT

Structured Cabling is defined as building or campus telecommunications cabling infrastructure that consists of a number of standardized smaller elements (hence structured) called subsystems.

Structured cabling falls into the following six sub-systems:

Entrance Facilities is where the building interfaces with the outside world.
Equipment Rooms host equipment which serves the users inside the building.
Telecommunications Rooms are where various telecommunications and data equipment resides, connecting the backbone and horizontal cabling sub-systems.
Backbone Cabling as the name suggests carries the signals between the entrance facilities, equipment rooms and telecommunications rooms.
Horizontal Cabling is the wiring from telecommunications rooms to the individual outlets on the floor.
Work-Area Components connect end-user equipment to the outlets of the horizontal cabling system.
Structured cabling design and installation is governed by a set of standards that determine how to wire a data center, office or apartment building for data or voice communications, using Category 5 or Category 6 cable and modular sockets. These standards define how to lay the cabling in a star formation, such that all outlets terminate at a central patch panel (which is normally 19 inch rack-mounted), from where it can be determined exactly how these connections will be used. Each outlet can be 'patched' into a data network switch (normally also rack mounted alongside), or patched into a 'telecoms patch panel' which forms a bridge into a private branch exchange (PBX) telephone system, thus making the connection a voice port.

Lines patched as data ports into a network switch require simple straight-through patch cables at the other end to connect a computer. Voice patches to PBXs in most countries require an adapter at the remote end to translate the configuration on 8P8C modular connectors into the local standard telephone wall socket. In the U.S., no adapter is needed, as the 6P6C plug used with RJ11 telephone connections is physically compatible with the larger 8P8C socket and the wiring of the 8P8C is compatible with RJ11. In the UK, an adapter must be present at the remote end as the 6-pin BT socket is physically incompatible with 8P8C.

It is normal to see different colour patch cables used in the patch panel to help identify which type of connection is being carried, though the structured cabling standards do not require this, except in the demarcation wall field

Cabling standards demand that all eight connectors in Cat5/5e/6 cable are connected, resisting the tempation to 'double-up' or use one cable for both voice and data. This is generally a good thing as it means that they fully support features such as Power over Ethernet which require the so-far unused brown cables.

Structured Cabling Standards
The main structured cabling standards used in the USA and many other countries are:

A. TIA-526-7 “Measurement of Optical Power Loss of Installed Single-Mode Fiber Cable Plant “– OFSTP-7 - (February 2002)

B. TIA-526-14-A Optical Power Loss Measurements of Installed Multimode Fiber Cable Plant – OFSTP-14 - (August 1998)

C. ANSI/TIA/EIA-568-B.1 Commercial Building Telecommunications Cabling Standard Part 1: General Requirements: General Requirements, may 2001.

D. Adenda ANSI/TIA/EIA-568-B.1-1-2001, Addendum 1, Minimum Curve Radius for 4 pair UTP and ScTP cable, july, 2001.

E. TIA/EIA-568-B.1-2 Commercial Building Telecommunications Cabling Standard Part 1: General Requirements Addendum 2 – Grounding and Bonding Requirements for Screened Balanced Twisted-Pair Horizontal Cabling - (February 2003)

F. TIA/EIA-568-B.1-3 Commercial Building Telecommunications Cabling Standard Part 1: General Requirements Addendum 3 – Supportable Distances and Channel Attenuation for Optical Fiber Applications by Fiber Type - (February 2003)

G. TIA/EIA-568-B.1-4 Commercial Building Telecommunications Cabling Standard Part 1: General Requirements Addendum 4 – Recognition of Category 6 and 850 nm Laser Optimized 50/125 μm Multimode Optical Fiber Cabling - (February 2003)

H. TIA/EIA-568-B.1-5 Commercial Building Telecommunications Cabling Standard Part 1: General Requirements Addendum 5 – Telecommunications Cabling for Telecommunications Enclosures – (March 2004)

I. TIA/EIA-568-B.1-7 Commercial Building Telecommunications Cabling Standard Part 1: General Requirements Addendum 7 - Guidelines for Maintaining Polarity Using Array Connectors – (January 2006)

J. TIA/EIA-568-B.2 Commercial Building Telecommunications Cabling Standard Part 2: Balanced Twisted-Pair Cabling Components - (December 2003)

K. TIA/EIA-568-B.2-1 Commercial Building Telecommunications Cabling Standard Part 2: Balanced Twisted-Pair Cabling Components – Addendum 1 – Transmission Performance Specifications for 4-Pair 100 ohm Category 6 Cabling - (June 2002)

L. TIA/EIA-568-B.2-2 Commercial Building Telecommunications Cabling Standard Part 2: Balanced Twisted-Pair Cabling Components – Addendum 2 – Revision of Sub-clauses - (December 2001)

M. TIA/EIA-568-B.2-3 Commercial Building Telecommunications Cabling Standard Part 2: Balanced Twisted-Pair Cabling Components – Addendum 3 – Additional Considerations for Insertion Loss & Return Loss Pass/Fail Determination - (March 2002)

N. TIA/EIA-568-B.2-4 Commercial Building Telecommunications Cabling Standard Part 2: Balanced Twisted-Pair Cabling Components – Addendum 4 – Solderless Connection Reliability Requirements for Copper Connecting Hardware - (June 2002)

O. TIA/EIA-568-B.2-5 Commercial Building Telecommunications Cabling Standard Part 2: Balanced Twisted-Pair Cabling Components – Addendum 5 – Corrections to TIA/EIA-568-B.2 – (January 2003)

P. TIA/EIA-568-B.2-6 Commercial Building Telecommunications Cabling Standard Part 2: Balanced Twisted-Pair Cabling Components – Addendum 6 – Category 6 Related Component Test Procedures – (December 2003)

Q. TIA/EIA-568-B.2-11 Commercial Building Telecommunications Cabling Standard Part 2: Balanced Twisted-Pair Cabling Components – Addendum 11 - Specification of 4-Pair UTP and SCTP Cabling – (December 2005)

R. TIA/EIA-568-3 Optical Fiber Cabling Components Standard - (April 2002)

S. TIA/EIA-568-3.1 Optical Fiber Cabling Components Standard – Addendum 1 – Additional Transmission Performance Specifications for 50/125 μm Optical Fiber Cables – (April 2002)

T. TIA-569-B Commercial Building Standard for Telecommunications Pathways and Spaces - (October 2004)

U. TIA-598-C Optical Fiber Cable Color Coding - (January 2005)

V. TIA/EIA-606-A Administration Standard for Commercial Telecommunications Infrastructure - (May 2002)

W. J-STD-607-A Commercial Building Grounding (Earthing) and Bonding Requirements for Telecommunications - (October 2002)

X. TIA-758-A Customer-owned Outside Plant Telecommunications Infrastructure Standard – August 2004

European countries use another set of standards, the main one being ISO/IEC 11801.

Microsoft Certified Professional - MCP

granddomain — Sat, 01 Dec 2007 21:52:39 GMT

Microsoft Certified Professional (MCP) refers to both an individual Microsoft certification and a broader professional certification program.

To be an MCP, candidates must complete any one exam within the program. The MCP program offers multiple certifications, based on different areas of technical expertise. To attain these certifications, a candidate must pass a series of exams within the program. Popular certifications are MCP, Microsoft Certified System Engineer (MCSE), Microsoft Certified Solution Developer (MCSD) and Microsoft Certified Database Administrator (MCDBA).[1]

Some employers require or prefer certain MCP certifications for specific jobs. MCP curriculum revolves around Microsoft's operating systems. Other vendors have their own certification programs such as the Sun Certified Professional program, the Red Hat Certification Program, the Oracle Certification Program, the Cisco Career Certifications program, the Ubuntu Certified Professional program and the Apple Certification Program.

Each exam costs approximately US$125. Exams usually take between 2 and 3 hours to complete and consist of between 45 and 90 multiple choice, drag and drop, and solution building questions. In early 2006 Microsoft announced a return to simulated content within exams where students are required to perform certain common administrative tasks appropriate for the topic at hand.

In October 2005, Microsoft announced the restructuring of its certification by launching a three-tiered certification program.[2]

Certification Programs

Microsoft Certified Systems Engineer
Microsoft Certified Systems Engineer (or MCSE) is the best-known and premiere Microsoft certification. It qualifies an individual as being able to analyze the business requirements for information systems solutions, and design and implement the infrastructure required. As of 2007, the MCSE is available for two different product lines; Windows 2000 and Windows Server 2003, each of which requires a different set of exams.

For the MCSE 2003, candidates must pass six core design exams (Four networking exams, one client operating system and one design exam) and one elective exam, for a total of seven exams. For the MCSE 2000, a candidate needs to pass five Core Exams (Four operating system exams, one design exam) and two electives. For the MCSE NT 4.0 (which is no longer available to earn, though it is still recognized as a valid certification), a candidate needed to pass four Core Exams (Networking Essentials, Windows NT Workstation, Windows NT Server and Windows NT Server in the Enterprise) and two electives.

The topic of these exams include network security, computer networking infrastructure, Active Directory, Microsoft Exchange Server, Microsoft SQL Server, and other topics of both general networking interest as well as specific Microsoft products.

Perhaps due to controversies over the term Engineer, this qualification has also been pejoratively referred to as Minesweeper Consultant and Solitaire Expert.

Microsoft Certified Solution Developer
The Microsoft Certified Solution Developer (MCSD) certification is the highest level programming certification offered by Microsoft. To fulfill the requirements of the certification, a total of five exams (four core exams, one elective exam) must be passed. Some of the core exams are also requirements for the MCAD. Microsoft has declared that this certification will be focused towards the needs of developers using .NET Framework 1.0 and 1.1 versions. Developers using .NET Framework 2.0 and Microsoft Visual Studio 2005 are expected to consider undergoing Microsoft Certified Technology Specialist (MCTS) and Microsoft Certified Professional Developer (MCPD) certification.

Microsoft Certified Systems Administrator
The Microsoft Certified Systems Administrator (MCSA) certification certifies a user's knowledge in system administration of Microsoft Windows operating systems and is generally simpler than, but not a subset of, the MCSE. The Windows Server 2003 MCSA is achieved upon passing 2 networking system exams, a client operating system exam (generally Microsoft Windows XP), and an elective exam. The Windows Server 2000 MCSA title is granted after taking 3 core exams and one elective. Although the MCSA is not a subset of the MCSE, it is possible to gain an MCSA on the way to an MCSE without doing any exams that are extraneous to the MCSE.

Whereas the MCSE is supposed to certify a person's ability to "plan, design, and implement Microsoft Windows server solutions and architectures in medium- to large-sized companies", the MCSA certifies a holder's ability to "implement, manage, and maintain the typically complex computing environment of medium- to large-sized companies".

Like the MCSE, the MCSA is available as "MCSA on Windows 2000" and "MCSA on Windows 2003" as of 2005. There exist two specializations for both tracks: Messaging and Security.

As an alternative to the electives on the MCSA electives table, certifications or certification combinations may substitute for an MCSA elective. For example, CompTIA A+ and Network+ together or CompTIA A+ and Server+ together can be credited and substituted for an elective through a Microsoft and CompTIA partnership agreement. One may also substitute Security+ alone which counts for the elective and one of two exams for the "Security Specialization." Security+ counts for MCSA 2003 and MCSE 2003. This is just one cost effective way to earning an MCSA if candidates are already certified in other areas.

Microsoft Certified Database Administrator
The Microsoft Certified Database Administrator (MCDBA) credential is for database administrators, who implement and administer Microsoft SQL Server databases. The certification is appropriate for individuals who derive physical database designs, develop logical data models, create physical databases, create data services by using Transact-SQL, manage and maintain databases, configure and manage security, monitor and optimize databases, and install and configure SQL Server. This certification requires passing three core exams, and one elective exam. According to Microsoft, people who operate MSSQL 2005 should apply for other certifications such as the MCITP (Microsoft Certified IT Professional) or MCTS (Microsoft Certified Technology Specialist), rather than the MCDBA. Complete course lasts 250 hours.

Microsoft Certified Desktop Support Technician
The Microsoft Certified Desktop Support Technician (MCDST) is a lower-level credential that demonstrates a technician can competently support end users and troubleshoot desktop environments running on Microsoft Windows. MCDST candidates are required to pass two core exams. Elective exams are not required. Complete course lasts 50 hours.

Microsoft Office Specialist
The Microsoft Office Specialist (MOS), previously named Microsoft Office User Specialist (MOUS) is a certification for using the Microsoft Office suite of business applications. While listed under the MCP Certification Programs, it is not officially an MCP Certification. The MOS exams are managed by a third party company, Certiport.

It appears (January 2007) that a new set of qualifications will replace the MOS/MOUS certifications for Office 2007. The direct application specific skills are the “Microsoft Certified Application Specialist” (“MCAS”) for each Office 2007 Application. And, a new “Microsoft Certified Application Professional” (“MCAP”) based on how to complete more common business tasks. While these qualification exams will be managed by Certiport it appears other exam providers may also become involved.

Microsoft Certified Trainer
The Microsoft Certified Trainer (MCT) certification is for individuals who intend to train users wanting to obtain any of the other certifications. They must have some type of certification out of the Microsoft Course. For example, in Australia, many MCT's have a diploma or degree in teaching either primary school or secondary education. It is also a requirement by many training companies, especially Microsoft Gold Partners to have MCT's with a degree in teaching.

Microsoft Certified Professional
Anyone passing just one operating system based exam, can be certified as Microsoft Certified Professional (MCP)(270, 271, or 272). (Except for exam 70-058: Networking Essentials since it isn't a product exam).

Microsoft Certification Resources
There are several courses, Boot camps, and practice tests from different vendors offering preparation material for Microsoft certification exams. Bootcamps normally provide residential program that includes food and lodging. These courses are meant for busy professionals who do not have enough time for self preparation or wish to get trained by professional trainers. Microsoft Press provides several books towards Microsoft certification exams preparation. Books are normally the first place to explore Microsoft certification options, and preparation. Apart from Microsoft Press books, there are other reputed publishers like Sybex, and others. In addition to books, Microsoft Learning also offers courses for each of the exams.

Apart from books, there are several practice tests vendors that offer pre-certification exams. These mock exams almost mimic actual exams, and normally priced much less than the actual exam. Several user forums are available for certification preparation where most questions are answered by other forum users.

Experts and past candidates recommend not only reading more than one book, but spending a good amount of time practicing the concepts on computers on a test environment. After practicing and reading, it's also recommended to take sample exams before taking the Microsoft exam.

Microsoft New Generation of Certifications
Microsoft has released a new three-tiered certification hierarchy. It consist of three series and four credentials that introduce an entry-level Technology Series, a Professional Series comprised of an IT Professional and Professional Developer credentials and a new top-level Microsoft Certified Architect.

There exist three series:

Technology Series
Professional Series
Architect Series

Technology Series
The seven Microsoft Certified Professional Developer (MCPD) Technology Specialist (MCTS) certifications are:

Technology Specialist: .NET Framework 2.0 Web Applications
This certification requires that one pass the following examinations:

Exam 70-536: TS: Microsoft .NET Framework 2.0 - Application Development Foundation
Exam 70-528: TS: Microsoft .NET Framework 2.0 - Web-Based Client Development

Technology Specialist: .NET Framework 2.0 Windows Applications
This certification requires that one pass the following examinations:

Exam 70-536: TS: Microsoft .NET Framework 2.0 - Application Development Foundation
Exam 70-526: TS: Microsoft .NET Framework 2.0 - Windows-Based Client Development

Technology Specialist: .NET Framework 2.0 Distributed Applications
This certification requires that one pass the following examinations:

Exam 70-536: TS: Microsoft .NET Framework 2.0 - Application Development Foundation
Exam 70-529: TS: Microsoft .NET Framework 2.0 - Distributed Application Development

Technology Specialist: SQL Server 2005
This certification requires that one pass the following examination:

Exam 70-431: TS: Microsoft SQL Server 2005 - Implementation and Maintenance (http://www.microsoft.com/learning/mcp/mcts/sql/default.mspx)

Technology Specialist: SQL Server 2005 Business Intelligence
This certification requires that one pass the following examination:

Exam 70-445: TS: Microsoft SQL Server 2005 Business Intelligence - Implementation and Maintenance (http://www.microsoft.com/learning/mcp/mcts/bi/default.mspx)

Technology Specialist: BizTalk Server 2006
This certification requires that one pass the following examination:

Exam 70-235: TS: Developing Business Process and Integration Solutions Using Microsoft BizTalk Server (http://www.microsoft.com/learning/mcp/mcts/biztalk/default.mspx)

Technology Specialist: Live Communications Server 2005
This certification requires that one pass the following examination:

Exam 70-262 TS: Office Live Communications Server 2005-Implementing, Managing, and Troubleshooting (available early 2006) (http://www.microsoft.com/learning/mcp/mcts/livecomm/default.mspx)

Technology Specialist: Microsoft Windows Mobile 5.0 Applications
This certification requires that one pass the following examination:

Exam Exam 70-540: TS: Microsoft Windows Mobile 5.0 - Application Development (http://www.microsoft.com/learning/mcp/mcts/mobility/default.mspx)

Professional Series
These certifications are based around .NET 2.0, Visual Studio 2005 and SQL Server 2005.

Microsoft Certified Professional Developer (MCPD)

Professional Developer: Web Developer
This certification requires that one pass the following examinations:

Prerequisite: MCTS: .NET Framework 2.0 Web Applications
Exam 70-547: PRO: Designing and Developing Web Applications by Using the Microsoft .NET Framework

Professional Developer: Windows Developer
This certification requires that one pass the following examinations:

Prerequisite: MCTS: .NET Framework 2.0 Windows Applications
Exam 70–548: PRO: Designing and Developing Windows Applications by Using the Microsoft .NET Framework

Professional Developer: Enterprise Applications Developer
This certification requires that one pass the following examinations:

Prerequisite: MCTS: .NET Framework 2.0 Web Applications
Prerequisite: MCTS: .NET Framework 2.0 Windows Applications
Prerequisite: MCTS: .NET Framework 2.0 Distributed Applications
Exam 70–549: PRO: Designing and Developing Enterprise Applications by Using the Microsoft .NET Framework

Microsoft Certified IT Professional (MCITP)

IT Professional: Database Administrator

IT Professional: Database Developer
=====IT Professional: Business Intelligence Developer=====
MCITP : Enterprise Support Technician - current
MCITP : Consumer Support Technician - current
MCITP : Server Administrator - Feb 28th, 2008
MCITP : Enterprise Administrator - Feb 28th, 2008

Obsolete Certification

Microsoft Certified Professional + Internet
Microsoft Certified Professional + Internet (MCP+I) requires passing three exams: Windows NT 4.0 Server, TCP/IP for Windows NT 4.0 Server and Internet Information Server 4.0 (or IIS 3.0 + Index Server)

Microsoft Certified Professional + Site Builder
Microsoft Certified Professional + Site Builder (MCP+SB) requires passing three exams: Windows NT 4.0 Server, Microsoft Site Server 3.0 and Microsoft FrontPage 98 (originally FrontPage 97)