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