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Cover Story: Unleashing of a fast Cat

The speed and performance improvements offered in category 6 will mean higher capacity, throughput and productivity for both networks and users. Clearly, it is the smart choice for all new cabling system implementations.


November 1, 2002  


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Now that the Category 6 cabling standard is a reality, many people are asking themselves a myriad of questions. What is it? Does it look and behave differently than Category 5 / 5e? Will it supercede Category 5 / 5e? Does it work? Have all the issues been resolved? What does it mean for network performance? What are the applications that will work on Category 6 that don’t work, or don’t work as well, on Category 5e cabling?

One of the biggest observable differences is in the cable construction. From the outside, Category 6 cables have a larger overall diameter, to a greater or lesser extent depending on the design. The diameter of Category 6 cables are in the range of 0.21 to 0.25 inch (5.3 – 5.8 mm) compared to Category 5/ 5e, which is in the range of 0.19 to 0.22 inch (4.8 – 5.5 mm).

This is because Category 6 cables are manufactured with larger copper conductors and may include an internal divider called a cross-web that serves to separate the pairs within the cable and reduce cross-talk noise. The cross-web divider to separate the pairs is not a specified requirement of the Cat 6 standard, and some manufacturers have developed designs and processes that deliver full

Cat 6 compliance without the use of any physical dividers between pairs.

The reason for the larger conductor size (approx. 23 AWG) is to provide a lower Insertion Loss (also called Attenuation) over the specified frequency range. A lower Insertion Loss means a stronger signal at the Receiver compared with Category 5 / 5e.

This improves the noise immunity to external and internal noise sources. Additionally, cables with a lower Insertion Loss can support longer distances or a higher temperature range for certain applications while continuing to deliver full Cat 6 performance. Even if you’re not a cabling expert, most of us will recognize that lower Insertion Loss is the functional equivalent of a strong signal, and we all know that signal strength is the critical factor in overall network performance.

Another feature of Category 6 cables is a very tight twist length of 0.5 inches or less to reduce crosstalk interference between pairs. Altogether, these differences are analogous to buying a car. There are many different models to choose from that come in different sizes and shapes and with different features and performance. Category 6 cabling, with its larger conductors, internal dividers, and tighter twist lengths would be analogous to a high-end model delivering better performance and more capacity.

WHAT ABOUT INSTALLATION?

Category 6 cables and components are installed very much the same way as their Category 5 / 5e counterparts. However there are some design and installation issues that the contractor and the installer must pay greater attention to, including the cable terminations and the cable pathway fill. The larger physical cable diameter needs to be taken into account when routing cables at cross-connects and in provisioning cable pathways.

When terminating Category 6 cables it is very important to ensure that the pair twists are maintained right up to the point of termination. It is particularly important to follow manufacturer’s instructions for terminating connectors. A poor termination can significantly reduce performance margins or cause test failures in the field.

From a cost/benefit perspective the doubling effect of Category 6 performance versus Category 5/5e performance for as little as a 20 per cent pricing premium deserves careful consideration. And the equation improves if you factor in the reality that the ‘technology window’ and operational life span of Category 6 systems will far out reach Category5/5e systems.

So, even with a new technology, an old adage rings true; it may be ‘penny wise, but pound foolish’ to implement new Category 5/5e systems today only to be forced to replace them in the near future because continually evolving IT systems need Category 6 performance.

To paraphrase from a famous film that suggested “If you build it, they will come,” the Cat5/5e to Cat 6 migration would be better described as “If you don’t build it, they are coming anyway.” As we see with all technologies, the need for ‘more’ and ‘faster’ are inevitable and irresistible forces that must be considered in your cabling infrastructure decisions.

HAVE ALL THE BUGS BEEN IRONED OUT

Category 6 connecting hardware needs to be qualified with a range of “high” and “low” test plugs that simulate worst case variations in the field. This means that a specific connector design may work optimally with certain plugs while only achieving minimum Cat 6 performance with other plugs.

So while the important concept of interoperability is delivered in the Cat 6 standard, it is most likely that optimum performance would be achieved using connectors and cords from the same vendor.

A simple way to describe Category 6 connector performance is to think of a parameter called sensitivity and selectivity on radio or TV receivers. Let’s take the example a Satellite Dish Receiver. When the technician comes to install the satellite dish he points it in the general direction of the satellite. While watching the signal level on the TV set or listening to an audible beeper, the technician adjusts the dish up and down, left and right to get the strongest signal.

It is the same way with a plug / jack connection. There is a minimally acceptable signal level depending on the orientation of the dish and an optimum signal when it is in the best alignment.

The Category 6 connector specification defines the deviation allowed and the minimum signal level to achieve interoperability. So, as you can see, Cat 6 does deliver on its promise. The work done by the engineering committee is a significant accomplishment in the industry considering the level of detail, completeness and the quality of the Category 6 standard as delivered.

In retrospect, a curious fact comes to mind that is true for all technology standards and perhaps especially true for cabling standards. New standards represent significant new performance targets that we must stretch while under development.

On publication of the standard, these distant targets instantly transform from projected upper thresholds to the absolute minimum acceptable performance values allowed under that standard. While the Cat 6 might have gone further, the published standard provides a solid step forward and our vision of higher performance systems will be achieved through a natural evolution in the marketplace.

WHY NOT SKIP CAT 6 AND GO ALL THE WAY TO OPTICAL FIBER?

Without even considering the issue of relative performance, the copper/fiber decision has been driven historically by the significant differences between the initial costs of copper versus fiber cabling plants, combined with the even greater differences between the costs of electrical versus optical networking devices.

Overall, the comparatively high total cost of ownership for optical networking made it very difficult to justify for use in horizontal distribution except where environmental noise, or security, or ultra high performance requirements made copper solutions impractical or inoperable.

Today, the cost differential between copper and fiber cabling is decreasing, however even as the cost of optical fiber becomes more comparable to copper, the largest deterrent to the use of fiber continues to be the cost of the active optical networking equipment.

To research information for this article, we ‘shopped’ equipment prices and availability on the Internet. There are a plethora of choices that provide 100 Mb/s Fast Ethernet ports over copper to the desktop and fewer choices over fiber.

Looking at relative prices from a leading manufacturer of networking equipment, a 48 port 100BASE-TX switch with two 1000BASE-X uplinks is US$4,500 (approximately US$80 a port for 100 Mb/s) compared with US$4,900 for a 12-port 100BASE-FX switch (approximately US$400 a port).

In this particular example, the cost per user port for the optical switch was more than 400 per cent higher than its copper-based counterpart. Generally, the cost of o
ptical networking equipment is from two to four times higher than copper.

As an alternative option, an end user can purchase a media converter with copper equipment. The added cost of media converters for multimode fiber is about US$112 per port for Fast Ethernet and US$385 per port for Gigabit Ethernet. In addition, some may be concerned over the reliability/manageability issues that may arise from introducing additional points-of-failure in the network.

All this means that running fiber to the desk is not economically attractive for today’s applications compared to copper, and the continually increasing performance envelop of copper cabling systems would seem to be more than adequate for horizontal distribution now and in the foreseeable future.

Another reason that supports high performance copper cabling to the desk is the need for remote powering for VoIP telephones and other devices. This is an important new development.

IEEE is in the process of developing a DTE Powering standard that would enable end users to plug in a variety of devices into the data outlet connector in the wall. The networking equipment or the mid-span power source would detect and recognize the type of device, e.g. an IP phone, sensor, camera, etc. and deliver the appropriate power as required by the device.

This is an important step towards a ubiquitous network that is designed for device independence. When powering remote devices, Category 6 cabling has advantages over Category 5e because of the lower DC resistance (23 AWG) and ‘Pair Balance’ recommendations, which is a new parameter for Category 6 components.

The new CAT 6 standard includes specific requirements for Interoperability between different vendors’ products as well as full Backward Compatibility with all existing Category 5 / 5e cabling, as this was a major objective in the development of the standard.

From a performance perspective, if we use Bandwidth and Signal-to-Noise Ratio (SNR) as the key indicators of performance, Category 6 cabling provides twice the Bandwidth (200 MHz) and 16 times (12 dB) better than Signal-to-Noise margins compared with Category 5e cabling.

These additional performance margins compensate for deficiencies in the equipment and external noise and temperature variations in the environment. Category 6 is well positioned to support demanding applications such as multi-channel broadband video with an extended frequency range up to 550 MHz and digital video signals as high as 2 Gb/s for HDTV and future multi-Gigabit applications.

Category 6 cabling is also a better alternative to fiber-to-the-desk because the cost of electronics is significantly lower for copper compared to fiber.

Finally, the new IEEE standards for remote powering of DTE equipment would be better served with Category 6 cabling because of the lower power dissipation for Category 6 cables and the improved balance recommendations for Category 6 components.

These performance improvements offered by Cat 6 systems means higher capacity, throughput and productivity for your networks and your users. The forward-looking Cat 6 specifications should produce an extended operational life span and protection of your Cat 6 infrastructure investment.

This combination of performance, longevity, and investment protection, along with the new attributes of interoperability and backward compatibility, makes Category 6 the smart choice for all new cabling system implementations. CS

Paul Kish is Director, IBDN Systems and Standards with NORDX/CDT. He is the current vice-chair of the TIA TR-42 engineering committee responsible for telecommunications cabling standards for commercial and residential installations. The author would like to thank Warren Davies of NORDX/CDT for his insight in developing the article.

To paraphrase from a famous film that suggested “If you build it, they will come,” the Cat5/5e to Cat 6 migration would be better described “if you don’t build it, they are coming anyway.”

How cabling parameters affect network performance

The relationship between the cabling parameters effectively boils down to the Signal plus the Noise that appears at the input of a Receiver. Let’s look a simplified block diagram of a Receiver (see below). The first block is a Receive filter that filters out all the noise outside the pass band for the application. For example, Fast Ethernet and Gigabit Ethernet uses a pass band of 125 MHz. This means that mobile phones that transmit at 900 MHz or higher do not have any effect on the performance of the network, no matter how close they are to the cable. These noise signals are effectively filtered out.

The second block is an equalizer that amplifies the signal to compensate for the Insertion Loss degradation of the Channel. It does nothing to change the Signal-to-Noise Ratio (SNR) since the Signal and the Noise are both amplified by the same amount. However, it restores the signal to close to what it was at the input of the Channel.

The last block is the most important. The digital signal is sampled at the clock frequency. The detector must detect the different signal levels in the presence of noise. If the noise is too high, it will generate bit errors. BER stands for Bit Error Rate. The maximum bit error rate that is acceptible for Ethernet networks is 1 error in 10 billion bits of information transmitted. A bit error will require a retransmiision of the information and can significantly slow down your network. A one per cent re-transmission rate reduces data throughput from 100 per cent to 20 per cent.

Taking all the noise sources into consideration, including Alien crosstalk (crosstalk from adjacent cables), a Category 6 channel delivers a stronger Signal and less Noise at the Receiver (SNR is about 10 dB better). The net result is a more robust channel that is less sensitive to transceiver impairments and environmental noise, and most important, that delivers a higher data throughput for your network.

PAUL KISH


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