Ethernet Signal Preservation In Factory-Terminated Patch Cords for Local Area Networks

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ONE of the most commonly asked questions with the introduction of the TrueNet™ Structured Cabling System is, “Why do you only offer patch cords in certain lengths?” Specifically, those lengths are 4, 7, 10 and 15 feet. An electrical impulse takes the shape of a sine wave. A wave has two components: the amplitude and the frequency (frequency can also be called wavelength). The amplitude is the “height” of the wave. The frequency, or wavelength, is the number of peaks in a given timeframe (see Figure 2). And the simple answer is: certain patch cord lengths cause unacceptable signal reflection and distortion to...

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Nội dung Text: Ethernet Signal Preservation In Factory-Terminated Patch Cords for Local Area Networks

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. KRONE: 800-775-KRONE www.kroneamericas.com www.truenet-system.com. 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.