of Structured Cabling
Training Programs and Equipment
- The Cabling
- The choice of network cabling
(or communication medium as it is sometimes called) is rather
important because of the extremely high frequencies of the signals.
Sending a 60-cycle utility power through a wire rarely presents
a difficulty; but sending a 100 million bits per second signal
can be a little more tricky. For this reason, the method of sending
signals and the materials they are sent through can be important.
- Network Cabling Types
- A number of cabling options
are available for networking connections.
- Unshielded Twisted pair (UTP)
- UTP cable is the primary cable used for networks, as specified
in the EIA/TIA 568 standard. This cable type has been widely
used because it is inexpensive and simple to install. Limited
bandwidth (which translates into slower transmissions) has pushed
development of new cable grades (the "cagegories" of
568) but has created a more expensive product and more complicated
- Screened Twisted pair (ScTP)
- Same as UTP with an overall shield around the 4 pairs. While
not currently specified for any networks or covered in the EIA/TIA
568 standard, it is used in many networks in Europe where EMI
is a greater concern. It tends to be more expensive, harder to
terminate and requires special plugs and jacks.
- Shielded Twisted Pair (STP)
- Like UTP but with a shield around every pair. Widely used in
IBM systems (IBM Type 1 cable) and included in 568.
- Coaxial Cables - Original Ethernet,
used in CATV systems. This is familiar and easy to install, has
good bandwidth and lower attenuation but more expensive, bulky.
Not included in 568, but in 570 for residential use.
- Optical Fiber - Optional for
most networks, top performance, excellent bandwidth, very long
life span, excellent security but slightlly higher installed
cost than twisted pair cables, more expensive electronics interface
to them. Cost efffective with optimal architecture. See Lennie
Lightwave's Guide To Fiber Optics.
- Other transmission options:
- Wireless - no data transmission
cables are reqired to connect any individual terminal, but requies
cabling to every antenna, so it's hardly "wireless"!.
Within the range of the radio signals, a terminal can be moved
anywhere. Usually more expensive but used in locations where
is would be difficult to install cables.
- Infrared Transmission - Also
transmits without wires to the terminal by using infrered (IR)
light but each transmitter requires cabling. By sending pulses
of infrared light in the same patterns as electronic pulses sent
over cables, it is possible to send data from one place to another.
Networks based on IR transmission have been developed for use
in office and for line-of-sight transmissions between buildings.
- Powerline or Phone Line Transmission
- Networks using available cabling with mixed results.
- Unshielded Twisted Pair
- Because networking evolved over
severeal decades, many different cabling solutions have been
used. But today, virtually all VDV copper cabling has moved to
unshielded twisted pair (UTP) as specified in the EIA/TIA 568
standard because it has been inexpensive, may already be in place,
is familiar to installers and is simple to install. (The cost
and simplicity of installation has changed a bit, however, with
Cat 6, see below.)
- UTP cable is comprised of four
pairs of carefully twisted pairs of copper wire, insulated with
carefully chosen material to provide high bandwidth, low attenuation
and crosstalk. UTP cable works so well because it is used with
transmitters that work on "balanced transmission."
They transmit equal but opposite signals on each wire of the
pair so each wire has only half the amplitude of the final signal.
The electrical and magnetic fields of each wire are opposite
and cancel out eachother, producing low electromagnetic emissions.
Likewise, electromagnetic pickup is the same on both wires so
they cancel out.
- We'll say it here and many times
more before we're through - the secret ingredient of Cat 5e/6
is the twists! In order to maintain Cat 5e/6 performance, especially
crosstalk, you absolutely must keep the twists as close as possible
to the terminations!
- The cable is terminated mostly
in jacks, connector receptacles that have punchdown terminations
on the backside and tricks inside to prevent crosstalk. See
Terminations. Some snap into work area outlets, others are
incorporated in rack mount patch panels. 568 allows many possible
cable configurations, including intermediate punchdowns, but
a direct run from a work area outlet to a patch panel will provide
the highest performance, likely necessary if upgrades to fast
networks like Gigabit Ethernet are contemplated.
- Patchcords for connecting network
equipment to the outlet or patchpanel are usually purchased factory-assembled.
The connector (plug) is properly called a "modular 8 pin"
but usually is referred to as a RJ-45, which is actually a specific
telco use of the same plug. They use stranded cable for flexibility
and require special connectors. Order them to proper length if
you can to prevent the mess that patch panels often become after
a few moves and changes.
- Right now, you can get hardware
and cable rated for Cat 3, Cat 5e or Cat 6. With cable, it's
easy to see the difference; it's in the twists - higher performance
cables have more twists. But jacks are harder to tell the differences.
Trust us - they are different. If you terminate Cat 5e cable
with Cat 3 jacks, you will get Cat 3 performance - no better!
When dealing with Category 5e and Cat 6 designed to support Gigabit
Ethernet, termination procedures become even more complicated!
Instead of the "Categories"
used in the US, in Europe and much of hte rest of the world they
use "Classes" to designate performance. Here's a table
of performance and correllations to US standards.
- (Not currently under consideration)
a guide to the diferences in the categories.
- Future Enhancements
- Like everything else that deals
with computers and communications, the speed of networks is going
up. Cat 5e is OK to handle one gigabit networks, but the EIA/TIA
TR 42 committee that writes the cabling standards (the same "568"
we referred to earlier) approved the standard for Cat 6 cabling
in June of 2002 after three years of debate, discussion and testing.
- This standard includes cables,
plugs and jack, patch panels and patch cords, in other words,
everything you need to install a complete cabling system. Performance
specifications for Cat 6 are for significant advances over Cat
5e - with attenuation and crosstalk performance almost as good
at 200MHz as Cat5e at 100 MHz. The result is that the attenuation
of a Cat6 link at 100 MHz is about 40% less than Cat 5e and crosstalk
(NEXT) is almost 10 times better.
- So using Cat 6 will give you
more "headroom" - better signal to noise ratios - which
can mean more robust data transmission on Fast Ethernet and Gigabit
Ethernet (1000base-T) networks.
- Cat 6 never found a real reason
for existence. Gigabit Ethernet ran fine on Cat 5e (some manufcturers
say it runs well on Cat 5 now) and when 10 Gigabit Ethernet came
along, it could only run on fiber optics. The copper suppliers
would not allow their product to be bypassed by technology, so
an "augmented" Cat 6 was proposed for 10GbE. The problem
seems to be not within the cable itself, but in crosstalk with
adjacent cables, called "alien" crosstalk. No doubt
some solution will be found, but fiber remains the most reliable
solution for GbE and above.
- This leap in technological advances,
like all previous ones, comes with a cost. The goal of the committee
is that each generation of Category-rated cable be "backward
compatable" which means that any networking product that
works on Cat 3, 5 or 5e is supposed to work on Cat 6. The other
issue that the group wrestles with is "interoperability"
- mixing and matching components. This part of the standard states
that cable plant containing mixed categories (eg: Cat 5e patchcords
on a Cat 6 cabling systems) is supposed to work without compatibility
issues, but will only work at the level of the minimum component
specification (Cat 5e in this case).
- Finally, there is the issue
of compatibility among different manufacturers products. Practically
everybody told users installing "pre-standard" Cat
6 to stick to one manufacturer's products or those tested for
compatibility. Now the EIA/TIA press release on the Cat 6 standard
states: "To ensure generic cabling system performance, Category
6 component requirements are specified to be interoperable when
products from different manufacturers are mated". The word
from insiders, however, is that there are some details still
to be ironed ont.
- And while the Europeans are
working on Class F - a 600 MHz cabling system, the EIA/TIA TR42
committee has declined to consider such a standard in the US
due to lack of interest from the network development committees.
- Network Cable Handling
- The performance of the cabling
network is heavily dependent on the installation. The components
used in structured cabling installation have been carefully designed
and exhaustively tested to meet or esceed the requirements of
EIA/TIA 568 for performance at 100 MHz. If the cable is not properly
installed, performance will be degraded. See the page
on installation for more tips.