and high-speed demands are pushing the limits of data
transmission in cable assemblies. The demands of advanced
applications such as Fast Ethernet, CDDI, ATM and Gigabit
Ethernet require better methods of determining whether
cabling systems can reliably transfer voice, video and
data information. Cable assembly suppliers say they
are stepping up to the plate with solutions. As networking
demands escalate, new and forthcoming network applications
have higher and higher data transmission rates
Back in the days of 10 Base T, you could run data on
web string or barbed wire. Five years ago you could
hook up a relatively generic cable and use it for testing
and be pretty certain it worked. Now you're getting
a lot more emphasis on the interconnect and cable because
you're pushing the limits of what copper is capable
of doing. Today we need to run data over some really
fast speeds, all the connectors and cable assemblies
have to be absolutely dead perfect because you can't
get away with any variances. We're finding out that
most of the assemblies used in our business just won't
make it in the very high-speed data transmissions. The
industry has to be reinvented.
Importance of structured cabling
cabling infrastructure is the most important part of
a network, and an essential building block without which,
a system may fail to function properly or at optimum
efficiency. All too often, organisations fail to identify
the importance of structured cabling systems and do
not allow for future expansion as more and more bandwidth
is required to cope with ever more demanding business
applications. Although the sluggish movement of data
is usually blamed on hardware or software, 70% of all
network problems are related to cabling systems.
It is very unlikely that businesses that wish to continuously
upgrade to the latest network technologies will ever
see a cable plant with a lifespan of more than five
years. Considering the trend in the recent past, with
technology of 1985 the thick and thin coax supporting
10-Mbps Ethernet is still being used. Later in 1987
we started using the UTP to support 10Base-T, and in
the early 1990s was replaced by Cat3 and soon thereafter
by Cat4. By 1995 we were looking at 100Base-TX Fast
Ethernet over Cat5. Cat4 was available for only a very
brief time because Cat5 followed so quickly on its heels.
In just 10 years we progressed through five cabling
Five years later, in 2000, Gigabit Ethernet (1000Base-T)
revealed deficiencies in some Cat5 installations. So,
in early 2001, Cat5 had already been superceded by Cat5E.
Cat4 and Cat5 are both defunct, and the development
of Cat6 standards is well under way. Cat6 promises to
replace Cat5E within a year or so and there's also talks
of developing a Cat7 standard!
/ TIA / EIA Cabling Standards and LAN Applications
available at this time
available at this time
evolving Cat 7
cabling standards remain uncertain. Few people believe
that Cat 7 will ever be viable. If and when a version
does arrive, it will not be UTP; existing proposals
call for a shielded or screened twisted pair (STP or
Everything about Cat 7 promises to be outrageously expensive
and extremely difficult to install. The cable will be
heavier and bulkier, costing more to ship and install,
and if the shielding is not grounded properly it will
create more problems than UTP ever had. There are significant
physical differences between category 6 and category
7 components. The "fully shielded" construction
of category 7 cable results in a larger outside diameter
and less flexibility than UTP or ScTP. These attributes
require greater care in the design of pathways and termination
spaces to allow for more space and larger bend radii.
Another potential problem is backward compatibility
among cabling standards.
Now consider the 1000Base-T Gigabit Ethernet, which
always energizes all four pairs at once! The bi-directional
dual duplex transmission scheme employed by 1000Base-T
actually requires each end of a channel to transmit
on one conductor of each of the four pairs simultaneously.
The specifications for ANSI/TIA/EIAC at 5 come nowhere
close to supporting such an application. This is one
of the primary reasons for developing newer cabling
Categories such as Cat6 and Cat7. There are other problems
with Cat7, most notably crosstalk and return loss, which
are two of the biggest problems faced when attempting
to support greater bandwidths.
pending category 7 and class F standards will enable
shielded cable installations to perform to their full
potential in terms of bandwidth over twisted-pair cabling,
versatility and ease-of-use. Category 7 cables will
be "fully shielded", with individually screened
twisted-pairs and an overall shield. This type of cable
is dominant in several European countries. However,
its global acceptance has been impaired by connecting
components that are limited in terms of performance,
ease of use, adaptability, and size. A category 7 interface
that is specifically designed for fully shielded cables
will overcome these connectivity issues.
Category 6/class E delivers the highest level of transmission
performance available without individually screened
pairs. For the vast majority of business and institutional
applications, 250 MHz bandwidth is more than adequate
for the life of the cabling system, making category
6/class E the perfect choice for generic premises cabling.
The goal for category 7/class F is to be as good or
better than any other type of balanced media for each
transmission parameter. For example, the channel will
deliver positive power sum ACR up to at least 600 MHz.
Another difference is with the connecting hardware.
The pending category 7 specification requires connectors
to provide at least 60 dB of crosstalk isolation between
all pairs at 600 MHz. This requirement is 32 dB more
severe than category 5 at 100 MHz, and 20 dB more severe
than category 6 at 250 MHz
Category 7 cabling advantages
Higher Bandwidth of up to 600 MHz as compared with
Cat 5e (100 MHz) & Cat 6 (250 MHz)
Suitable for installing in strong RFI & EMI environment
Individual pair shielding enable better NEXT isolation
allowing different application to run in the same
Lower cost than using a fiber LAN
Moving from existing copper based LAN without having
to change the existing electronics.
Secure transmission shielding keeps signal within
Category 7 cabling disadvantages
Individual pair and overall shielding increases the
overall weight and size of cable. Hence needs larger
& stronger pathway and more stringent bend radius
(100 mm or 4 inch)
Individual pair and overall shielding means higher
labor cost and longer time to terminate cable.
· Bandwidth of 600 MHz is it truly useful·
May have earth loop problems, if both ends of the
cable are connected to ground.
FIBER OPTIC SOLUTION
between Copper and Fiber-optic solutions is sometimes
difficult, as distance, cost, required bandwidth and
specialized expertise need to be considered.
WHICH IS MORE PRACTICAL?
the telcos are still using single mode fiber over ten
years old and have upgraded from 145 MB/s to over 2.5
GB/s with no problems - and more is coming.
After proposing a solution for GigaBit Ethernet that
ran on Cat 5, the proposal for Cat 5 required bi-directional
signals on each pair, with multilevel coding to compress
the data. With the bi-directional use of each pair,
things like FEXT (far end crosstalk) and return loss
(reflections at the interfaces) became critical issues.
The transceiver needed digital signal processing at
very high speeds to make it work.
Now the proposal seems to be changing to "lets
run on a higher bandwidth cable plant and use less expensive
electronics." The option is Cat 6. And if this
proposal wins out, users will not be running Gigabit
Ethernet on installed cable plants, unless, of course
they are fiber! And if they have to install new cabling,
will fiber be the medium of choice? At some point, it
will be cheaper to use fiber than to "S T R E T
C H" the UTP copper any farther.
The Moore's Law of Fiber Pricing?
Moore's Law? It's credited to Gordon Moore of Intel
and it states that the cost of computing power is halved
every 18 months. Well, the very same price decline appears
to be happening in fiber!
An excess supply of fiber coupled to the end of several
key patents relating to the manufacture of the fiber
appears to be causing severe erosion in the price of
fiber. Imports of cheaper fiber made overseas are likely
with the expiration of some of the patents.
Optical fiber cabling development
2500 BC Roman Times Glass is drawn into fibers·
1790 Claude Chappe invents "Optical Telegraph"
1958 Alec Reeves begins investigating optical communications
at Standard Telecommunication Laboratories
The rest is history - Wide use of Optical Fiber Cable
Advantages of Fibre Optic cables
Long distance transmission
Immune to RFI & EMI
Intrinsic security of transmission
Reduced system costs
Reduced maintenance costs
Lowest life cycle costs
Synergistic planning lowers overall system cost factors
3 Potential disadvantages
Potentially higher cost than copper
Requires higher skilled labor to terminate than copper
Fiber connectors are less forgiving of abuse than
Common questions on optic fibre cabling
What are the different types of fibre available?
What are the figures used to describe them ?
There are three types of fibre available in data networking
- 50/125mm multimode fibre, 62.5/125mm multimode fibre
and 9/125mm single mode fibre.
The figures 50 mm, 62.5mm and 9mm refer to the diameter
of the inner glass core in which the light travels.
The figure 125mm refers to the diameter of the glass
outer cladding. As each fibre shares the same outer
diameter, the mechanical properties of the fibres are
identical. However, the optical properties vary significantly.
Multi mode fibres have a large core, which allows less
critical alignment and can be used with low cost LED
technology. However, because of the core diameter the
bandwidth is limited.
Single mode fibre, on the other hand, has almost unlimited
bandwidth due to the small core supporting only one
light mode. But, this requires very high precision alignment
in both joints and connectors and the need to use expensive
laser technology to drive the fibre.
These factors combine to make a single mode installation
approximately four times more expensive than a multi
How is the distance over which a fibre can be used
related to attenuation and bandwidth?
specifying a fibre, the two main attributes are attenuation
of a fibre (or link) is the light loss through the fibre
(of system) measured in decibels. The task of measuring
the loss of a link is relatively simple process using
a light source and power meter at the required wavelength.
This attenuation component of the fibre or link, along
with the bandwidth of the fibre, characterizes the fibre
link and data rate/distance capability of that link.
In the past, bandwidth over fibre was never much of
an issue. There was always far more bandwidth than existing
electronics could interface with. Now, however, bandwidth
has become a significant factor due to the emergence
of new applications such as the Gigabit Ethernet standard.
In the past, at low data rates, the usable distance
over fibre links was dictated by the attenuation, i.e.
by the link loss budger. Now, due to the much greater
bandwidth requirements of Gigabit Ethernet, we find
that some multi mode fibre types are limited in usable
distance by bandwidth rather than loss. The date rate
versus length of a fibre link is related to the bandwidth
of the fibre but is also a factor of the transceiver
technology. The simplest way to demonstrate the length
limitations of the various protocols of fibre types.
Sreelal can be contacted at firstname.lastname@example.org