CAT 6 Cabling–The Right Choice For Data

A s data rates and user aspirations soar higher, fibre-to-the-desk

might look like the most rational choice. Cost considerations and a reluctance

to ditch proven technology, however, provide pretty compelling arguments for

sticking with copper wiring technologies, and for an obsolescent technology,

conventional copper cabling is showing remarkable vitality.

Faster data rates demand more highly specified cables.

Nonetheless, to strike a new balance, a new wiring system, Category 6, is being

suggested. The proposal has not met universal welcome and this article sets out

to provide an unbiased summary of the all the arguments.

First, it is worth taking a quick refresher course as to

better understand where Category 6 stands vis-à-vis the present status quo.

The Category system applied to cables has a North American

origin with an attempt to create a universally accepted classification system

for Unshielded Twisted Pair (UTP) wiring. Underwriters Laboratories (UL)

collaborated with the manufacturer, Anixter, and developed a "Level"

programme in which there were five levels of increasing quality of cabling. In

1994, the UL system was harmonized with the Category system of the American

Electronics Industries Association (EIA) and the Telecom Industry Association (TIA)

and the term "Level" was replaced by "Category". Categories

1 and 2 are excluded as they are not recommended for data applications and the

EIA/TIA Category rating system only identifies Categories 3, 4, and 5.

Category 3 applies to UTP cables and associated connecting

hardware with transmission characteristics up to 16 MHz. It is also known as

voice-grade. Whilst Category 4 covers cables and connectors with transmission

characteristics up to 20 MHz, data-grade Category 5 is for UTP cables and

hardware with transmission characteristics up to 100 MHz. While some cable

vendors rate their cables up to 350 MHz, the ISO and EIA/TIA do not specify

cables and connectors beyond 100 MHz.

Whilst most data cables produced and installed today are

defined as Category 5 and carry data at a speeds well below their tested rating

of 100 MHz, there is nonetheless a clear expectation that data rates will soon

exceed this limit. Next generation LAN offerings are beginning to appear with

data rates up to 100 Mbps. The move to ATM-to-the-desk will employ channels

rated at 155 Mbps and eventually at 622 Mbps.

Trends such as these are pushing the cable industry to design

and produce cables that are defined to even higher frequencies in the 300 MHz to

600 MHz region. Accordingly, a proposal for a new Category 6 cable has been

submitted by the International Electrotechnical Commission (IEC), defining cable

parameters up to 300 MHz. It has been approved for further study,

notwithstanding some opposition.

Category 6 cable would certainly simplify distribution at

higher data rates. In theory it is not impossible to transmit 622 Mbps

information over Category 5 cable. But in reality, the only way of realizing

this would be to split the data across all four pairs of the Category 5 cable

and send it unidirectionally (first transmit, then receive). Clearly this would

degrade performance and is not a realistic proposition. A Category 6 cable would

offer up to double the functionality of Category 5–but at a cost. For

minimizing cross-talk and adequate EMC compliance each of the four pairs must

have individual screening. This increases the physical size and weight of the

cable, as well as the minimum bending radius. Worse, the individual shielding

around each pair will render it too large to be accommodated within a standard

RJ-45 connector, implying the cost of developing and manufacturing a new design

of plug and socket.

Replacement



The consequence is that any upgrade to Category 6 will involve systematic

replacement of connectors and other modules, as well as a redesign of patch-bay

paneling to accommodate this new hardware. This is hardly welcome news for many

users who have already invested major sums in Category 5 cable and apparatus, in

many cases sold to them with a 15-years’ guarantee. For Category 6 to take

off, extremely cogent reasons will have to be found for installing it.

A move towards higher data rates is one driver and has

already been mentioned. Another incentive is the feeling of reassurance offered

by a future-proof installation–the so-called "feel good" factor. It

is still very much an unknown territory though and manufacturers are also

investigating means of upgrading current Category 5 products to meet the

perceived need for additional "headroom".

Greater Cost



Accompanying the greater bulk and cost of Category 6 cable and connectors

that is already mentioned will be a demand for increased precision in the way it

is installed. This appears to hold no fear for German users, who are the

mainforce for adopting Category 6 and who have written a draft DIN (German)

standard for it. In fact, it is stated that between 10 and 20 percent of new

installations there use Category 6 cable now.

Elsewhere, however, there is less enthusiasm extending to

outright opposition in some quarters across the Atlantic where the push is for

Enhanced Category 5 with an unshielded option. Any agreement and full

standardization must, therefore, be at least one, and probably two, years away.

In the meantime our best advice to users is to await the

outcome of these machinations. Of course, the "right" cabling

architecture is always the one that meets the users’ needs in the most

efficient way, taking due consideration of the LAN-type services required now

and in the future. The need for Category 6 cabling is probably overstated and in

our opinion, there will be no difficulty in accommodating ATM-to-the-desk in

existing Category 5 wiring techniques.

Highly Specialist



Applications truly needing Category 6 cable are unlikely to appear within

next two years and even then, they will be highly specialist, niche-type

operations. If, for all this, customers feel obliged to anticipate the future

Category 6 standards, then our advice is to fit cable with individually screened

pairs along with Enhanced Category 5 connectors, changing out the latter once

Category 6 connectors are standardized and become available.

DS Nagendra is manager (Premise Networks), KRONE Communications Ltd, India