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.

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.

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.

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.

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.

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.

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

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 shall 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 IEEE wiring 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.

A. It sounds like costs were an issue when this building was cabled, but if it is configured for Ethernet (using pins 1, 2, 3 & 6) it should be OK for 10BaseT. I wouldn’t like to speculate on whether it will run at higher speeds because that is dependent on the quality of the installation and the amount of network traffic.

If the installation was originally wired for Token Ring then it will use pins 3, 4, 5 & 6 which will not work with Ethernet.
Crosstalk could be an issue if the pairs have been split between outlets and/or between pins on the jack, (pins 1 & 2 should be a pair and 3 & 6 should be a pair).

I hope this helps, and although it is possible that you will have no problems, I would strongly advise a rewire. This is because it will be easier at this time to carry out the work and, as you move to higher speeds in the future this wiring configuration will undoubtedly start to cause problems.

A. This is a big question!

First of all, we are in the ‘Information Age’ and more and more households are using the internet and have more than one computer. Because of this, home networking is becoming commonplace and it is a more efficient method of connecting two or three computers to the internet over one phone line or DSL (Digital Subscriber Line).

The main benefits of installing the cabling during construction are the cost and ease of implementation. Cable is fairly inexpensive and installing it during the building work is far easier than trying to do it once the property is finished and decorated. I get a lot of email from people all over the world who are cabling their houses to connect PC’s together, and hiding cables in wall cavities or chasing out and re-plastering is not an easy task for them, unlike most office environments where this is not such an issue.

Another point worth raising is that residential cabling is not just for connecting PC’s together. ‘Smart Houses’ also use intelligent devices such as alarm systems, refrigerators and heating/air conditioning systems all of which can be networked to a controlling PC or accessed via the Internet when you are away from home. OK, you may be asking why would we need to? but it is starting to happen. And, of course, the cabling system can also be used for telephones, which makes adding an extension phone as simple as plugging it in at the nearest cabling outlet and patching it through at the panel.

Q. For every pulse of light that is sent down a fibre optic cable there is some light which is lost because it is beyond critical angle and cannot be reflected. If part of this mode is lost then doesn’t that mean the data is sent as incomplete? How can the computer make sense of an incomplete signal? Could you explain this situation.
A. The data is sent as a stream of bits and so the amount of light that is lost merely reduces the strength of the signal. The pulses of light that reach the other end will have lost some of their strength but they will still be large enough to reassemble into bytes of information. Multi-mode transmission simply means that the light travelling down the fibre will take multiple paths, it does not mean that each mode is transmitting different data. Each pulse of light comprises all modes.

Q. Finally, I know that the time between transmitting each pulse must be enough so that the first pulse completely arrives at the receiver before the second pulse does. What happens if two pulses do crossover one another? Do they mix to create a different pulse, does the PC say transfer error, or the screen freezes etc.?
A. The pulses all travel at the same speed so it is not possible for one to overtake another. The main reasons for errors in a fibre system are too much attenuation (reduction in signal strength), and reflections or backscatter at poor connections which if large enough will interfere with the signal.

We tested them using a TBase cable tester, and they passed just fine. Looking at your diagram for correct wiring, it looks like you have some colored wires in different locations, but it is still pin for pin. Is there a reason why ours would be causing our problems?

A. Regarding your question on RJ45 pinouts, I would say that you are probably experiencing crosstalk problems.

The reason is this, Ethernet uses pins 1 & 2 and 3 & 6 on 10/100BaseT networks (I know it’s a funny way to do it but thats how it is!). One pair is used for transmit and the other pair for receive, so pins 1 & 2 at one end will connect to pins 3 & 6 on the other end and vice versa. In the correct wiring configuration each signal path (transmit or receive) is on its own twisted pair of wires, the twists help to eliminate crosstalk. With your wiring, pins 3 & 6 are split between the green and blue pairs making them susceptible to crosstalk (or noise), this also gets worse when using higher speeds (100BaseT or Gigabit Ethernet).

The reason your tester didn’t pick it up is because it only tests for continuity, shorts, crossed pairs etc. (not split pairs) you would have to use a scanner (like the Fluke DSP4000 or MicroTest OmniScanner) to find a split pair.

Q. what are some advantages and disadvantages about star, ring, and bus topologies?

A. In answer to your question regarding Network Topologies I hope the following helps.

Bus Topology
Advantages – Simple to implement, all machines are ‘daisy chained’ which makes wiring as easy as stringing coax cable from one computer to the next and so on.
Disadvantages – Not very versatile when machines have to be moved, as rewiring part of the network is necessary. Not very fault tolerant, on some systems (10Base2) if one part of the bus is disconnected the whole segment of the network goes down. Not suitable for voice.

Ring Topology
Advantages – Fairly simple to wire. Quite fault tolerant, with a Token Ring network if the main ring is disconnected anywhere, the ring uses a loop back system to maintain ring integrity.
Disadvantages – It is only really used with Token Ring networks these days and it uses Type 1 cable, this is very bulky and is not really suitable for running voice. Again, moves and additions mean rewiring and re-routing cables.

Star Topology
Advantages – These days most buildings are cabled using a star topology with Cat 5e or Cat 6 cable. This gives the network a centralized wiring point which makes connecting and disconnecting machines as simple as plugging and unplugging an RJ45 connector in to a hub or switch (Ethernet, Token Ring and any other type of network or service that is required). It can also be used for voice, data, video and any low voltage application.

Disadvantages – Requires a centralized wiring point, which can be just a cabinet on the wall for small installations, or a dedicated air conditioned room with racks and cabinets in large office accommodation. On large installations the sheer bulk of cable coming back to the wiring closet can be difficult to control and keep tidy.

A. If you hold both of the RJ45 connectors side by side and look at them from the bottom (ie. the clip is away from you) you can make out which colour is connected to which pin. The pins you are interested in are (from left to right) 1 & 2 and 3 & 6. If they are the same either end then it is a straight through cable, if pin 1 (usually orange/white, but not necessarily) is connected to pin 3 at the other end and 2 is connected to pin 6 (and vice versa) then you have a crossover cable. If you look at the testing page of the Network Cabling Help website, about half way down there are some pictures of the pin outs for RJ45 connectors. The ‘crossed pair’ image is actually the correct wiring for a crossover cable and above it is the correct wiring for a straight through cable. If you have a straight through cable then it won’t work without a hub, if pins 1 & 2 and 3 & 6 are crossed over then the problem lies with the way the network is setup.

Cat 5 crossover cable?
Q. I have been looking at your site and it was very helpful.
I’m trying to connect two computers with a cat 5 crossover cable. The cable that I received in the mail was crossed correctly, but it was also crossed at 4 &5. My question is will this cable work by just joining PC to PC without any hubs or anything else. I bought the cable from an individual.

A. If you are using it for 10BaseT or 100BaseT Ethernet then the wiring should be 1 to 3, & 2 to 6
Pins 4 & 5 aren’t used on 10/100BaseT Ethernet systems so it should be OK. If you are planning to use Gigabit Ethernet or Token Ring then it won’t work.

Cable length limits?
Q. I know that cables have restrictions on distance, but I really would like to know why those limits are for each cable. E.g. Why is Cat X cable limited to 100m, and thinnet 185M etc. I have just accepted these values but have been asked why and I do not know a technical enough answer as I have never been a cabler. I could not find this on your site and was hoping it might be added or if you could email me back with why. Thanks.

A. The length limits are not for the particular cables as such, they are for the type of data signal that they carry.

Let me try and explain!

Thinnet (RG58 coax) was used for 10Base2 Ethernet, at 10Mbps on RG58 coax Ethernet can reliably operate upto a distance of 185m. The native cabling environment of the AS400 is Twinax and the standard operating speed is only 1Mbps. At this speed it has a maximum distance of 1800m, however, if Cat 5 forms part or all of the link the distance can drop to between 36m and 364m.

So for a proprietary network such as Thinnet, the distance is set at the maximum length that the signal will work reliably at a given speed over a given type of cable. So far so good!

Now, when we talk about Cat 5, 5e, 6 etc. these are cabling ‘Standards’ which define a method of connecting all types of networking protocols, over a cabling system that uses a common media, common connectors and a common topology. So the length limit was arbitrarily set for the worst case scenario. 10BaseT may well work on Cat 5 for 150m but ATM, AS400, Token Ring etc. may not, and because a structured cabling system has to work for all networking methods, a limit had to be set.

I don’t think I have explained this very well but I hope you get idea. Incidentally, I have heard talk of the length limit being dropped from the standards as it is the overall Attenuation to Crosstalk Ratio which determines a cables ability to transmit a signal successfully, and not the length of the cable. If anyone can elaborate on this point please let me know.

Cat 6
At last! the standard for Cat 6 has been approved for publication by the EIA (TIA/EIA-568-B.2-1). Category 6 is capable of transmission frequencies up to 250Mhz and has a positive power sum attenuation to crosstalk ratio upto 200MHz using improved cables and RJ45 connectors. The problem that manufacturers have, is that to meet the Cat 6 specification, requires the use of cables and connectors which are designed to work together as a ‘tuned’ system. This means that if you install a Cat 6 system the manufacturer will only guarantee performance if all of the components including the patch leads are from their Cat 6 product range. In fact, by mixing Cat 6 components from different manufacturers you could end up with a system with worse performance characteristics than a conventional Cat 5e system. That said, it is worth noting that Cat 6 systems are backwards compatible with Cat 5/5e cabling and when mixed with these lower bandwidth systems the performance criteria of the lower specification will still be met.

Testing Cat 6 cables can be a frustrating process, apart from taking longer because the tester has to scan frequency steps up to 200MHz instead of 100MHz, the fine line between pass and fail is accentuated it seems by the slightest kink and twist. The most significant factor when testing a Cat 6 system can be return loss failures due to the test leads themselves. All connectors have a life cycle and with the average RJ45 connector this is around one or two thousand insertions, so test leads should be replaced after every 1000 tests or so. OK, not a problem but at around $200 per set this cost will have to be considered when pricing jobs.

Fluke seem to have a solution to this problem with their DSP-LIA101S Permanent Link Adapters. The connector at the end of the leads are interchangeable and replaceable with connectors from different manufacturers to ensure compatibility with the system under test. Although a good idea, the adapters are over $500 and a new pair of “Personality Modules” cost over $100. Surely the test plugs should now be considered as ‘consumables’ and the price lowered to reflect this.

Cat 7
This is proposed to be a 600MHz system using a shielded cable with individually screened pairs and a new type of connector. The cable and connectors are slightly bigger than Cat 5e and installation time can be increased because of the complexity of the termination. There are two main draw backs with installing this type of cabling, the first is the additional cost involved, and the second is that almost all networking hardware uses RJ45 jacks. To connect to the cabling system, you have to use Cat 7 to Cat 5e patch leads, and because any system is only as good as its weakest link, your speed is back down to 100MHz. Ratification of the Cat 7 standard could be two years away by which time fibre might be a cheaper alternative.

Shielded or Unshielded
This is a subject that has been debated and argued over for a long time, and as yet, there are still no definite answers. Most countries in Europe, and in particular Germany, argue that apart from protecting data signals against high frequency noise from outside sources, shielded cable also protects the humans against the possibility of having their brains fried due to the effects of high frequency emissions from the cable itself. Other countries, such as the UK, US and Canada, aren’t particularly bothered by this because nothing has been proved, and after all, millions of people wander around with mobile phones pressed against the side of their heads with no apparent side effects, er… yet. My advice would be to install unshielded cable unless the customer insists on a shielded system.

Shielded cables and components are more expensive and are more time consuming to terminate, you should also bear in mind that a shielded cable that isn’t properly grounded has worse performance characteristics than an unshielded cable. If a shielded cable isn’t grounded at all, the screen can act like an antenna and induce all manner of noise on to the data signal.

Low Smoke Zero Halogen
In public buildings, such as airports, shops and hospitals, then the cable should be Low Smoke Zero Halogen (LS0H or LSZH).

• 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!

There are also lots of books on the subject of cabling and a selection of these can be found at Amazon.com, 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.

The next thing to do is open accounts with the suppliers of data cabling materials in your area, or try some of the online suppliers. One such company is Network Cables Online.