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- Ethernet Signal Preservation In Factory-Terminated Patch Cords for Local Area Networks
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- Ethernet Signal Preservation
In Factory-Terminated Patch Cords for Local Area Networks.
ONE
of the most commonly An electrical impulse takes the shape of a sine wave. A wave
asked questions with the has two components: the amplitude and the frequency
introduction of the TrueNet™ (frequency can also be called wavelength). The amplitude is
Structured Cabling System is, the “height” of the wave. The frequency, or wavelength, is
“Why do you only offer patch cords in certain lengths?” the number of peaks in a given timeframe (see Figure 2).
Specifically, those lengths are 4, 7, 10 and 15 feet.
Amplitude
And the simple answer is: certain patch cord lengths
cause unacceptable signal reflection and distortion to
Ethernet signals, leading to errors and poor network
throughput. Factory-terminated 4, 7, 10 and 15 foot
TrueNet cords prevent this distortion, preserving the
integrity of 10/100Base-T Ethernet signals.
Wavelength
What is an Ethernet signal?
Figure 2: Sine wave.
The explanation of what an Ethernet signal is, is rather
complex. In fact, in order to begin, it is first important to The illustration below (Figure 3) shows four different
understand the composition of an Ethernet signal. sine waves, each with the same amplitude, but having
varying frequencies.
An Ethernet signal is designed to mimic the binary language
of computers (ones and zeros), by creating a signal which
can be sent over a distance. One of the binary signaling
methods that is easiest to understand is Morse code, where
a quick “dot” is one and a long “dash” is zero. Ethernet
uses electrical impulses to create a signaling method which
also can be interpreted as zeros or ones. The basic idea is to
create a square wave, seen below (Figure 1), where the
instantaneous changes up and down are used in indicate the
one or zero. Using electrons to create a signal that looks like
a square wave is somewhat tricky, but here is the basic idea:
Figure 3: Sine waves of varying frequencies.
In order to create a signal that looks like a square wave,
you need to create a signal which combines many
frequencies together (see Figure 4).
The key component to remember is that the square wave
of an Ethernet signal is made of many different sine waves,
each important to creating the shape of the square wave.
Figure 1: The square wave of an Ethernet signal.
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No part of this document may be reproduced without permission ©2000 KRONE, Inc.
- + =
Add sine waves of different frequencies together...
And it starts to
Add even more frequencies... look like a
The key component
square wave!
to remember is that
the square wave of
an Ethernet signal
is made of many
different sine waves,
each important
to creating the shape
Figure 4: The square wave of an Ethernet signal is made of many different sine waves combined together.
of the square wave.
The next important thing to understand is that Ethernet Ethernet signals and patch cords
expects the size and shape of the square wave to fall within
We pointed out that an Ethernet square wave is made up of
a set of defined boundaries, so that the signal can be
the sum of many sine waves. If anything should happen to
properly interpreted. One example of these boundaries is the
the energy in one or more of those sine waves as they travel
rise and fall time, or the time that it takes to indicate a
down the wire, the shape of the square wave can change.
change in state (see Figure 5). If either of these parameters
To look at it another way, if you remove any one sine wave
don’t fall within the prescribed limits, a “one”might be
from the square wave, the shape changes. Therefore, it is
misinterpreted as a“zero” (which would cause an error).
critical to ensure that signal energy is preserved as a signal
travels along a wire, so the shape of the wave stays consistent.
As a sine wave is generated, the greatest amount of energy
Rise Time Fall Time is released at peaks of the cycle (since a sine wave oscillates
around a zero line, peak energy occurs at the “peak” and
“valley” of each cycle) (see Figure 6). If anything happens to
Voltage
disrupt the wave at these points, the signal strength of that
wave is severely compromised. As it turns out, the most
disruptive elements to signal strength in a network node are
the connection points. Remember that any node in a
Nanoseconds
network consists of a number of connections between the
signal-generating ends (the NIC and the hub/switch). Patch
Figure 5: Rise and fall time is the length of time, in nanoseconds,
that it takes for a signal to rise or fall from one state to another,
cords are plugged into the station outlet, patch panels, etc.
signaling a “one.”
The reason that connection points are disruptive is two-fold.
Now, “What does any of this have to do with patch cord First, it represents a transition of physical materials and
lengths?” To get to the answer, we have to go back geometry which occurs in the path of the signal. This
to the sine wave. disruption is further exacerbated when the connected
KRONE: 800-775-KRONE www.kroneamericas.com www.truenet-system.com.
No part of this document may be reproduced without permission ©2000 KRONE, Inc.
- physical distances where the peaks and valleys of the wave
Maximum occur. It is therefore possible to determine the optimal
Energy length of a patch cord so as to position the first connection
point at a physical distance where minimum energy
is occurring (see Figure 8).
Zero
Energy The most important thing to do is to minimize the energy
reflection at the sine wave frequencies that are most critical
to the shape of the square wave. For 10/100Base-T Ethernet,
the frequencies of greatest concern are the approximate
window between 10 MHz and 31 MHz.
Wavelength
Patch cord lengths which do not take this distortion effect
into account can allow maximum energy at the critical
Maximum
frequencies to be present at the connection point, which
Energy
has the effect of distorting the square wave, and causing
bit errors in Ethernet.
Figure 6: As a sine wave is generated, the greatest amount of
energy is released at peaks of the cycle.
The technique of using specific patch cord lengths to reduce
elements are not electrically matched well. The second errors has been confirmed with active network analysis of
reason is that the connection points are usually very close to bit error generation in otherwise identical patch cords
one of the active sending elements of the network (NIC or
plugged into the same channel. Patch cords of the proper
hub), where signal strength is the strongest, and has the
length generated no errors, while patch cords of the
most energy. The first connection point is obviously the
incorrect length returned error after error. De-embedded
patch cord. Therefore, the integrity of patch cords is critical
electrical testing also confirms this result, in the form of
(see Figure 7).
excessive return loss on the resonance producing lengths.
When the sine waves hit the connection point, if any
wave is at its point of maximum energy, one of two Consequently, the decision was made with the launch of the
things can happen: TrueNet patch cord line to only include lengths which are
1. The energy can be reflected back toward the source. “safe” for use in Ethernet systems. These lengths are 4, 7, 10
2. The energy can be dissipated and lost. and 15 feet, respectively. Other lengths from 1 to 20 feet
can produce unacceptable error generation under normal use.
In either case, the shape of the sine wave is distorted,
which then can distort the square wave.
All TrueNet cords are 100% performance tested and
Since the wavelength of a sine wave actually corresponds to factory terminated to the proper lengths to ensure
a physical length in meters, it is possible to determine the optimum performance.
Patch Cord Connector Connector
Patch Cord
NIC HUB
Horizontal Cable
Figure 7: The patch cord represents the first, and most critical, connection point in the network.
KRONE: 800-775-KRONE www.kroneamericas.com www.truenet-system.com.
No part of this document may be reproduced without permission ©2000 KRONE, Inc.
- Wavelength
Zero
Energy
Maximum
Energy
Zero
Energy Maximum
Energy
Resonance Producing Length
NIC
Non-Resonance Producing Length
NIC
Figure 8: TrueNet patch cords are available only in lengths “safe” for Ethernet systems.
The philosophy of the TrueNet system is to eliminate the
root causes of poor throughput in structured cabling All TrueNet cords
systems. Fortunately, the benefits of patch cords that do not are 100% performance
have error-causing lengths is demonstrable in any cabling tested and factory
system, even if no other TrueNet components are used. terminated to the proper
Bottom line — certain lengths of patch cords generate lengths to ensure
errors, others do not. KRONE is committed to providing only optimum performance.
KRONE, Inc. the best possible data transmission solutions to the
North America Headquarters marketplace. KRONE’s TrueNet patch cords have been
6950 South Tucson Way designed from the ground up to preserve the integrity of
Englewood, CO 80112-3922
Ethernet signals.
Telephone: (303) 790.2619
Toll-Free: (800) 775.KRONE
Facsimile: (303) 790.2117
www.kroneamericas.com
www.truenet-system.com
KRONE: 800-775-KRONE www.kroneamericas.com www.truenet-system.com.
No part of this document may be reproduced without permission ©2000 KRONE, Inc.
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