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April 1997
By Andrew Cray
Cabling
Wiring for Speed, Playing for Time
With new high-speed LAN technologies on the way, the search is on for capable cable
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MORE INFO
Cable Ready
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Wired today, mired tomorrow: That's the sticky situation for net managers planning faster LANs. Much of the copper cabling in use now can't handle the high-speed technologies that are on the way. The good news is that there's a way out of the cabling conundrum. Net managers have four choices when it comes to wiring for speed--but those who don't want to get caught by surprise should start looking at the alternatives now.
One place to start is with so-called enhanced Category 5 copper,
which carries data at higher speeds than ordinary Cat 5. There's also
"Category 6" cabling--it moves traffic much faster than today's
copper. Fiber is another alternative, with the undeniable benefit of
virtually unlimited capacity. Finally, net managers could go with new
signaling schemes that standards bodies are developing, which will
permit big-bandwidth apps to be run over traditional Category 5.
Trouble is, none of these options come through on all fronts. While
enhanced Cat 5 carries data at higher speed
s, it's still not the
lightning fast medium networkers really need--nor is it standardized.
There are no standards for Category 6, either, and it's also more
expensive than enhanced Cat 5. Pulling fiber to the desktop means
loosening the purse strings even more. Finally, new signaling schemes
aren't ready yet, with the technology said to be at least two years
away. That's why for speeds above 155-Mbit/s, the ATM Forum is simply
recommending fiber.
On the Wire
Running high-speed data over UTP (unshielded twisted pair) copper
wiring is no easy trick. Currently, the fastest standardized cabling
is Category 5, approved in 1995 by the Telecommunications Industries
Association (TIA) in the U.S. and by the International Organization
for Standardization (ISO) internationally. It can carry data at
frequencies up to 100 MHz--more than adequate for fast Ethernet, which
has a frequency requirement of just 62.5 MHz, according to Amir Yaari,
cable design manager at Teldor Wires and Cables Ltd. (Ein-Dor,
I
srael), a cabling supplier.
But fast Ethernet is nothing compared with the next generation of
LAN protocols, and they're the ones that will cause the problems.
Gigabit Ethernet and high-speed ATM push frequency requirements into
the hundreds of megahertz--up to 350 MHz in the case of 622-Mbit/s
ATM, according to Poul Villien, coordinating manager at 3P Third Party
Testing A.P.S. (Copenhagen, Denmark), an independent test lab.
That's prompted some vendors to roll out enhanced Category 5 cable,
which typically can handle frequencies of up to 200 MHz. "Enhanced" in
this case refers to the fact that crosstalk levels are kept to a
minimum, which is what permits those high frequencies to be achieved.
The keys to keeping crosstalk down are manufacturing techniques.
"Primarily, it's done by refining the twist ratio between the four
pairs," explains Tony Beam, director of systems marketing at AMP Inc.
(Harrisburg, Pa.). "You've got to twist them more tightly, balance out
the pairs in relation t
o each other, and find the optimum
performance." Materials also matter. "It has a lot to do with the
quality and consistency of the copper wire," says Steven Elmore,
technical services specialist at Commscope Inc. (Hickory, N.C.).
Basically, enhanced Cat 5 is a higher grade of cable and is less
susceptible to the data loss that imperfect installation might lead
to. In other words, net managers are more likely to get the most out
of their copper.
Perhaps not surprisingly, this is reflected in the price--enhanced
Cat 5 costs about 20 percent more than ordinary Cat 5, according to
David Hess, the U.S. product manager for Alcatel Cabling Systems S.A.
(Brussels, Belgium), which owns several cable manufacturers. But the
cable is just one element of a complete installation: Factor in labor
and equipment costs and "you've got a 5 percent to 7 percent premium
for an enhanced category 5 cabling system," says AMP's Beam.
It didn't scare off Olivier May. He's director of information
systems at First Natio
nal Bank of Joliet (Joliet, Ill.). May paid AMP
$160,000 to wire 15 bank branches in Illinois, a price that included
the cable, connectors (like patch cords and patch panels), and labor.
Although May didn't check AMP's regular Cat 5 prices, he thinks he got
a good deal. "Once you pay the labor cost, you might as well install
the best cable you can get," he notes, saying enhanced Category 5 also
helps him gird for high-speed apps in the future.
And so far, nothing has gone wrong. But that shouldn't come as a
surprise, considering May's traffic is a mix of Ethernet and fast
Ethernet. After all, enhanced Cat 5 can't currently carry anything
faster. And simply forcing higher frequencies over enhanced copper
isn't the answer--it's unshielded, which means crosstalk would soar,
leading to intolerable bit-error rates.
All Talk
That 200-MHz limit also could cause enhanced Cat 5 to fall through
the cracks in terms of standardization. In the U.S., where most of the
world's enhanced cabling is s
old, a TIA committee is considering a
300-MHz minimum, according to chairman Paul Kish (although he stresses
that the exact level is yet to be determined). Only individually
shielded foil twisted pair (SFTP) cable, like that used in Europe,
meets the requirement--and users in the U.S. aren't likely to
acknowledge a spec that would force them to tear out the installed
base of enhanced Cat 5.
Vendors of enhanced Cat 5 aren't helping matters, sometimes playing
fast and loose when describing cable capabilities. AMP, Belden Wire &
Cable (Richmond, Ind.), and Berk-Tek Inc. (New Holland, Pa.) all
trumpet the fact that their enhanced Cat 5 products are tested to 350
MHz--even using that figure in product names (FutureLAN 350, Media
Twist 350, and LANmark-350).
Such tests, which most other vendors also run, prove only that
there are no kinks or irregularities on the cable's surface. They do
not prove that the cable works at that frequency, since, of course, it
can't. Tom Debiec, an application engineer
at Berk-Tek, admits that
the vendor is only trying to keep pace with the claims of other
vendors. "It started out as a marketing thing," he says.
Given this tendency toward confusion, net managers need to work out
an enhanced cable's usefulness for themselves. The best way to do so
is to look at the attenuation-to-crosstalk ratio (ACR) at specific
frequencies. Simply put, the lower the ACR, the greater the
deterioration in signal quality.
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BUILD YOUR OWN CUSTOM TABLE
A Selection of Enhanced Category 5
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The Category 5 cabling standard requires cables to operate with an
attenuation of 22 decibels and crosstalk of 32 dB when running at 100
MHz, for a minimum ACR of 10 dB. Enhanced Cat 5 boasts higher ACR
ratings, typically twice tho
se of regular Category 5. BICC Brand Rex
Ltd. (Glenrothes, U.K.) promises 20 dB at 100 MHz and 10 dB at 200
MHz--which meets the level 7 benchmark of Anixter Inc. (Skokie, Ill.),
the largest U.S. cable installer. In fact, many enhanced cables meet
this requirement (see
Table 1
). But this also puts those misleading
350-MHz claims in even finer perspective. "At 350 MHz, the ACR runs
negative," says Debiec.
Further, enhanced Category 5 cables are tested for powersum
performance. Powersum is a way of measuring crosstalk across all four
pairs, rather than just two. Since higher-speed LAN transports will
likely use four pairs to push data, powersum measurements give net
managers a more accurate indicator of how cables will handle the new
technologies (like gigabit Ethernet) when they arrive.
So what does all this mean? Net managers who buy enhanced Cat 5 are
getting no guarantees they'll be able to run higher-speed LAN
applications in the
future. What they are getting is some peace of
mind. "It's headroom," says Alcatel's Hess. "It's insurance."
Cat 6 or Deep Six?
But for networkers who want to run high-speed data over copper
cabling, insurance isn't enough. They want assurance--and that's where
an international Category 6 standard could help. Unfortunately, one
isn't likely to materialize soon. Cenelec (European Committee for
Electrotechnical Standardization, Brussels), the ISO, and the TIA are
trying to develop Cat 6 specs covering frequencies above 100 MHz--but
work in all three groups is stalled. Vendors can't seem to choose
between 300 MHz and 600 MHz as the minimum.
That's sparked the Deutsche Institut für Normung (DIN), the
German standards body, to issue its own "draft proposal"--with a
600-MHz minimum operating frequency as its centerpiece. "Germany has
been a little bit of a rogue," says Alan Flatman, an independent
consultant at LAN Technologies Ltd. (Congleton, U.K.) and a member of
the ATM Forum.
But the vendors are jumping on board. So far, about a dozen (mostly
European) cable manufacturers have announced conformance with the DIN
spec. In theory, their copper-wire cables should be able to carry
multigigabit data through copper wire. But there's a catch: It has to
be SFTP and not UTP. Not only is SFTP anathema to net managers in the
U.S. and other parts of the world (because of the installed base of
UTP), but also it can cost three times as much as UTP (see
"Wire Act
Leaves LANs Dangling," February 1996
).
And even if U.S. net managers did pay this much, it wouldn't be
worth their while. According to Geoff Thompson, manager of standards
development at Bay Networks Inc. (Santa Clara, Calif.) and chairman of
the IEEE's 802.3z (gigabit Ethernet) committee, there are no plans to
develop a gigabit Ethernet standard specifically for German Cat 6
cable--especially since gigabit Ethernet is slated to run over Cat 5
(once the standard appears). Further,
an internal statement recently
signed by George Dobrowski, chairman of the ATM Forum's Technical
Committee, indicates that the forum would never give approval to Cat 6
for 622-Mbit/s ATM. What it all boils down to is that without widely
accepted standards, few vendors are likely to develop products
specifically for Category 6.
There are other problems. European networkers installing Cat 6 are
probably using the wrong connectors. According to 3P's Villien, the
only connectors specified by the German draft are RJ-45 plugs, which
(because they're not optimized for Cat 6) allow only two of the four
pairs to be used. To get the full 600 MHz on all four pairs, net
managers need to buy expensive proprietary plugs, available from only
a handful of vendors.
Does that mean that Category 6 is a complete wash? Not exactly. Cat
6 cables are reasonably futureproof--with lots of headroom should
applications eventually be developed for them. Net managers who choose
Cat 6 may also be able to delay the shift t
o fiber longer than UTP
users, provided vendors continue to make the necessary connecting
hardware. Shielded cables also offer better protection against EMI
(electromagnetic interference) and are more likely to conform to the
tough EMI requirements in the European Union. And in countries where
Cat 6 already is in use, suppliers are likely to charge lower
installation fees than they would in the U.S.
Fiber Fund
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Join the discussion on Message Server about cabling.
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For net managers interested in true future-proofing, there's only
one option: fiber. There's also an obstacle: cost. Although pulling
fiber to the desktop is getting less expensive, it's still too rich
for the blood of most networkers. "I don
't believe it's priced
efficiently enough," says Joliet Bank's May. Although he's using fiber
for the vertical backbone wiring in Joliet's 15 buildings, he says
he'll stick to copper for horizontal runs.
It's not as though he isn't thinking ahead--Joliet Bank is planning
to install videoconferencing, check imaging, and other high-bandwidth
apps in the coming years. ("To do that, we'll probably install fast
Ethernet to the desk and ATM on the backbone," May says.) It's just
that he can't see the need for faster speeds to the desktop right
now.
What is it about fiber that makes it so pricey? Among other things,
there is the equipment that attaches to the end of each run. "The real
end-user price for a [copper] 10Base-T NIC [network interface card] is
between $50 and $80," says D'Arcy Roche, vice president and general
manager of premises systems at AMP. "For fiber they're a little under
$200." Just multiply that by the number of ports and users requiring
such cards, and it's easy to see how the costs
mount.
Still, Roche notes that fiber component prices are dropping. "The
price of an optical transceiver has gone down at least 25 percent over
the last 12 months," he says, adding that such reductions should
eventually filter through to end products.
There's more to the money picture than connecting hardware.
Although vendors disagree on whether fiber installation labor costs
are higher, net managers should take them into account. Barry Elliott,
product marketing manager at BICC Brand Rex, says fiber installation
is about 60 percent more expensive, since hooking up connectors is
tricky and performing tests takes longer. Roche isn't so sure. "That's
ridiculous," he says, noting that fiber is stronger and can be
installed more quickly. "When you roll the whole thing up, it's about
even."
Then there's the price of the fiber itself. "That's about 30
percent more expensive," Roche says; the figure is based on AMP's own
copper and fiber products. The cost of a total installation? That
depe
nds on the type of building, but for what it terms a typical
installation, AMP says running fiber costs 67 percent more (based on
wiring 72 users into a backbone closet). BICC cites a figure of 64
percent higher.
But AMP also stresses that straight copper-to-fiber comparisons can
be unfair; after all, copper runs are limited to 100 meters, while
fiber runs can reach up to 300 meters. That helps cut down on the
number of hubs and repeaters, which in turn cuts costs. Ultimately, in
the absence of a consensus, net managers are best advised to cost it
out for themselves.
Waiting to Encode
For some net managers, waiting it out might be the best strategy.
Standards bodies realize there's a huge installed base of Category 5,
and they're looking at ways to run high-speed protocols over copper
cabling. The IEEE, for instance, is working on a scheme for sending
gigabit Ethernet over copper. The ATM Forum already has a standard for
155-Mbit/s ATM over Cat 5. And at least one vendor says it's be
en able
to run 622-Mbit/s ATM over copper, although the scheme is likely to
remain proprietary.
The key to Cat 5 speed is advanced encoding. Unfortunately, most
methods for encoding data--such as NRZE (non-return to zero)--just
aren't very efficient. Newer encoding schemes like MLT3 address this.
For instance, fast Ethernet requires a frequency of 62 MHz using NRZE,
but only 31.25 MHz with MLT3.
Encoding schemes operate at the connector level--in the hubs,
switches, patch panels, and NICs. They also take up a lot of
processing power--so much so, in fact, that chip sets within the
interfaces need the equivalent of a 486 PC on every port, according to
the IEEE's Thompson.
According to Joe Skorupa, senior director of marketing for Fore
Systems Inc. (Warrendale, Pa.), that means that running gigabit
Ethernet over copper will be far too expensive--for the foreseeable
future. "Why are we doing this?" he asks. "There's a pretty fair
chance that it will cost as much for the copper version as f
or the
fiber." The IEEE is "counting on the large installed base of UTP,"
says Teldor's Yaari, adding that users will have to wait for vendors
to make the interfaces in bulk before prices come down.
On top of that, no one knows if gigabit Ethernet will even work in
most copper installations. "It's going to be very sensitive to
interference," warns Skorupa.
Standards might also be some time in coming. The IEEE has only now
started work on an encoding scheme to run gigabit Ethernet over
Category 5 UTP, and Thompson estimates it will be mid-1998 at the
earliest before it's done. In contrast, an IEEE spec for gigabit
Ethernet over fiber is expected by the end of this year.
As for ATM over copper, users can run 155-Mbit/s ATM on regular
Category 5 cabling--but the encoding scheme is fairly unadvanced. Net
managers should be sure they're getting a good installation, since
kinks in the line or cables being run more than 100 meters lead to
transmission failures, according to Yaari. "You must d
o a perfect
installation," he stresses.
But there will be no standard for speeds over 155 Mbit/s, according
to Flatman. The forum is instead concentrating its efforts on
622-Mbit/s ATM over fiber, expecting it to become the standard for LAN
backbones since most are based on fiber already.
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CONTACT AUTHOR
acray@data.com
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Nevertheless, there is at least one vendor with a proprietary
scheme for running 622-Mbit/s ATM over enhanced Cat 5. Lucent
Technologies Inc. (Murray Hill, N.J.) says its Systimax SCS cabling
system can deliver 155 Mbit/s over each of the four pairs, producing a
combined throughput of 622 Mbit/s. Systimax employs the 64-point CAP
(carrier amplitude phase) 64 encoding scheme to push data at
frequencies of 26 MHz over a distance of 100 meters. Meanwhile,
Nordx/CDT (Pittsburgh) sa
ys it has achieved 622 Mbit/s over enhanced
Cat 5 in the lab, but it isn't shipping products yet.
Andrew Cray is international new products editor for Data Communications based in London. His e-mail address is
acray@data.com
.
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