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Is CAT 6 out of the bag?
Some vendors have already released Category 6 compliant cables and related products. But is the standard stable as yet? by A Sitaramaiah

I guess the honest answer to the title of this article is, "We're working on it." Most manufacturers promote CAT 6 "compliant products" like cables, jacks, patch cords, and test equipment in the market place. IT professionals might remember that there was a similar entry of the Category 5 and Category 5e "compliant products" in the past. The so called "Category 6 compliant products" started to enter the market place in early 1998 and the list of products and suppliers continued to grow. However, number of questions remain unanswered. What is the real story—is Category 6 here or not? If not, where do we stand, why is it taking so long, and when will it be finished?

Standardization process
The standardization process actually began in late 1997 when ISO (International Standards Organization) proposed the objective of a cabling system called Class E/Category 6. The basic objective was to provide the same level of performance as Category 5 and twice the positive ACR (Attenuation Crosstalk Ratio). Since the positive ACR of Category 5 is 100 MHz, Category 6 was designed to provide 200 MHz.

Surprisingly, the basic objective for Category 6 cabling system performance formed in late 1997, has remained relatively unchanged till date. The most significant change occurred in 1998 when the IEEE (Institute of Electrical and Electronics Engineers) asked the TIA (Telecommunications Industry Association—an organization which sets telecommunications standards worldwide) and ISO groups to extend the testing to 250 MHz. They were asked to do so although the performance requirements at 200 MHz remained unchanged. So why is development on Category 6 still held up? The reason for the hold-up is largely due to interoperability between manufacturers.

Unfortunately, getting from Category 5 to Category 6 has been extremely challenging. Not only does the behavior of the components become more complex as frequencies get higher, our knowledge of what needs to be tested has changed as network protocols become more sophisticated. Category 5 specifications were based on two-pair applications like 10/100BaseT and Token Ring.

Gigabit Ethernet
Gigabit Ethernet has completely changed the way we view cabling system performance. 1000BaseT is unique because it uses all four pairs of the cable. And each pair transmits and receives at the same time. To accommodate multi-pair, bi-directional applications like 1000BaseT, additional parameters have been specified for Category 6 and Category 5e cables. The parameters are skew, FEXT (Far End Crosstalk), PSNEXT (Power Sum NEXT), and return loss (see box for explanations).

It seems that, more the cabling system technology evolves, more there is to learn. It has been determined that secondary signal reflections (those headed away from the transmitter) are a significant, additional source of noise not accounted for in other parameter measurements. The effect of these reflections shows up as differences between the actual insertion loss (attenuation) of a link or channel and the insertion loss as determined from adding the component losses. This ILD (Insertion Loss Deviation) is taken into consideration in the Category 6 standard.

Another 'new' performance parameter involved in the Category 6 standard is balance. Balance refers to the ability of the cabling system to cancel out ambient (common mode) noise picked up from the environment. The requirements for balance are still under discussion and are represented by placeholders in the draft standard.

So, where does the industry stand in the Category 6 development process? What will you get if you install a Category 6 system today? Well, the good news is that the system (channel and link) performance requirements for Category 6 has been stable throughout the development process and there are no indications that these system specifications will change. But the main issue of interoperability between manufacturers has yet to be resolved.

Issues to resolve
The biggest challenge faced by Category 6 product designers and the standard committee is the connecting hardware and patch cords. The performance of the jack is highly dependent on the plug connected to it. The jacks must be optimized to a certain range of plug performance. The definition of this range is still under discussion. Part of the problem is that the range is so narrow that it is difficult to measure consistently, from lab to lab. And until this issue is resolved there will be little interoperability between Category 6 products. The problem also affects manufacturers of field test equipment. Until all Category 6 jacks are tuned to a standard plug, test equipment will have to be provided with multiple test leads, each suitable for a particular jack.

Now that TIA has approved TIA/EIA-568-B.1 and is wrapping up TIA/EIA-568-B.2, the committee will be able to dedicate much needed time to Category 6. The TIA sent out the latest draft of the Category 6 standard for the internal committee ballot in December 2000. They have reviewed the comments in February 2001 and plan to send it out for an industry ballot. However, do not expect the standard to be finalized for several months at best. In the meantime, you should be fine as long as you stick with your system manufacturer of choice and are willing to accept system (channel and link) performance. Interoperability and support for the LAN systems like 1000BaseT, is not the issue. It is the ability to mix-and-match cable and connectivity products, specifically jacks and patch cords.

Definitions

Crosstalk: Interference from an adjacent channel.

Skew: A change of timing or phases in a transmission signal.

NEXT (Near End Cross Talk): A measurement of crosstalk between two wire pairs. It is the difference in signal strength between the interfering pair and the interfered pair. The higher the number, the less the crosstalk.

FEXT (Far End Crosstalk): A measurement of crosstalk between two wire pairs taken at the far end of the line.

PSNEXT (Power Sum NEXT): In a four-pair cable, it is the algebraic sum of the NEXT of the three pairs as they affect one pair and return loss.

The writer is Senior Manager, Systems Engineering & Marketing, Tyco Electronics Corporation India (P) Ltd.

 
     
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