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-Ã -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