The AirES product range of cables are a true innovation in structured cabling. In most evolutionary processes the gain in one attribute often sacrifices another. With the AirES evolution all attributes, both physical and electrical, are improved to provide a "Win Win" situation for both the installer and customer. This white paper will focus on the electrical attribute advantages of AirES. Herein, we will discuss the revolu- tionary development of the technology and the by-product effects on any and all electrical parameters. A full glossary of terms is included for further understanding. TrueNet ® AirES ® Technology Electrical Characteristics of the Evolution TrueNet ® AirES ® Technology: Electrical Characteristics of the Evolution Page 2 Background To fully understand the benefits of the TrueNet AirES solution, one must first understand the fundamentals of cabling and the hurdles overcome by this product. Good Dielectric Constant is key in producing high quali- ty data communications cable. The lower the Dielectric Constant of the insulation material, the better the resistance to breakdown when an electrical field is applied. Air, with a Dielectric Constant of 1.0, is the best of all insulators and is the basis by which others are measured. ADC has understood this and has been using air as an insulator in our connectivity products for many years. Below is an example of different materials and their Dielectric Constants. Water, Glass and Air were added to the list to give a better understanding as to what constitutes a good Dielectric Constant. It may be relevant to note the Dielectric Constant of Glass is higher than FEP insulation. This results in fiber optic cables having a lower Nominal Velocity of Propagation (NVP) than UTP copper cables. The NVP is the speed a signal propagates through a cable expressed as a percentage of the speed of light in a vacuum (300 m/sec) and given the value of 1. The NVP of a data communications cable can be directly calculated from the dielectric constant of the insulating material and differs with change in frequency. The speed of the signal over multi-pair data communi- cations cable is critical for high speed networks. This can be attributed to two main factors. 1. The speed at which the signal is traveling (NVP). 2. The total length of the cable pair, which allows for twist rate. Both of these parameters combined are measured as Propagation Delay or the time delay between the sent and received signal. One of the byproducts of using FEP as an insulation material over FRPE is an increase in the NVP due to its lower Dielectric Constant. The typical NVP of SAME design cables, using FEP as an insulator over FRPE, would typically increase up to 4% in NVP, therefore making FEP a faster insulating material. Below is a table of typical NVP values for different cable categories: Note the Type 1 cables of old had an advantage in NVP over current UTP designs, coming in at 78%. Type 1 cable is able to achieve much higher NVP values through the foaming of the insulation materials. This introduces air pockets within the dielectric. Air has a much better Dielectric Constant than FEP, thus increas- ing the signal speed. Type 1 cable was also shielded or PIMF (Pairs In Metal Foil) cable which allowed for crush resistance. This may also occur on unshielded foamed insulation materials. The AirES Innovation: ADC’s challenge was to develop a cabling insulation using air as an insulator, increasing NVP to the same levels as that of Type 1 cable, and at the same time, having a high level of crush resistance for UTP applica- tions. The use of foamed insulation in UTP cables can prove to have an adverse effect on the integrity of the structure, as it leaves the cable susceptible to crushing. By placing solid ribs around the entire conductor, crush resistance has exceeded the requirements of UL444 by more than 4X. Water PVC FEP Polyimide-Glass Flame Retardant Polyethylene Air 78.5 4.3 3.6 2.5 2.1 1.0 NVP= 1 √ ∑ r Cable Insulation Transmission Typical Type Material Type NVP Type 1 Foamed Token 78% Polyethylene Ring Cat 3 PVC 10BaseT 53% Cat 4 ECTFE 100BaseT4 63% Cat 5 FRPE 100BaseTX 66% Cat 5 FEP 100BaseTX 70% Cat 5E FRPE 1000BaseT 66% Cat 5E FEP 1000BaseT 70% Cat 6 FRPE 1000BaseT 66% Cat 6 FEP 1000BaseT 70% TrueNet ® AirES ® Technology: Electrical Characteristics of the Evolution Page 3 In the ADC AirES designed cables, AIR combined with traditional FEP has been introduced as an insulating material. The result is a NVP that parallels Type 1 cable and at the same time remains crush resistant. The total effect of using air combined with FEP as an insulation material is a 31% reduction in Dielectric Loss. Here’s how it works. The equation for working out the Dielectric Loss due to insulation type where E is the Dielectric constant of the insulation material and Fp is the power factor of the material is: Within the original equation both the Dielectric Constant and the Power Factor of the material are reduced with the introduction of air. The effect is a 31% reduction in Loss due to Dielectric. The obvious benefit to a reduced dielectric loss is a direct improvement to signal loss, i.e. stronger signal strength. This allows for a reduction in copper conduc- tor size without the sacrifice of performance on Attenuation, which has a greater impact on the mechanical attributes. Through the introduction of air pockets between the FEP and copper conductor the total Dielectric Constant is reduced. The capacitive effects are decreased*. This is then brought back to the nominal 100? by reducing the outer diameter of the insulation. The total effect is faster pair transmission on a smaller pair footprint. The effect of the faster NVP is low Propagation Delay. Currently the allowable Delay for Cat5e and Cat 6 is 570ns between transmitter and receiver. As mentioned before, the Propagation Delay is also a function of the length of the pair, including the twist. The greater the twist rate the longer the pair. The TrueNet AirES cable is able to reduce the amount of twist needed for each pair as well as increasing the NVP. *Impedance = the square root of the inductance (con- ductor effects) divided by the capacitance (insulation effects), or Loss = √ ∑ diel 9.12f * Fp Cable Insulation Transmission Typical Type Material Type NVP AirES Cat 5e FEP and Air 1000BaseT 78% AirES Cat 6 FEP and Air 1000BaseT 78% fep = 2.07 ∑ fep = 1.80 ∑ fep Fp = .00030 fep Fp = .0002 2 Or the Dielectric Constant of FEP Or the Dielectric Constant of FEP and Air in AirES Or the Power Factor of FEP Or the Power Factor of FEP and Air in AirES fep = .0039f Loss fep = .0027f Loss Dielectric Loss reduced by 31% 32% less cross sectional area 100 Ω 100 @ Ω 17% Reduced Distance AirES AIR pockets as an insulation material. Z = √ L C TrueNet ® AirES ® Technology: Electrical Characteristics of the Evolution Page 4 By reducing the capacitance, impedance is higher. This can be corrected by reducing insulation size, thus the AirES invention. This results in a Propagation Delay of ≤475ns, 17% bet- ter than the standard. Allowing for a more equal time delivery on Gigabit Ethernet. This makes the work of the electronics easier and gives more of a buffer for error free transmission. Delay Skew: Even more critical than the Propagation Delay is the Delay Skew, the difference in time each signal takes to arrive on all 4 pairs. For 10/100BaseT transmission this is not as critical since only 2 of the 4 pairs are being used for transmission. Delay Skew becomes important only when we migrate to 1000BaseT (Gigabit) tranmis- sion, as we are now transmitting on all 4 pairs at the same time. For optimal performance the signals should arrive at the receiver as close to the same time as possi- ble. The standards allow for up to 45nS in delay between the fastest and slowest pairs. There are other schools of thought that support a reduction to <25nS. The AirES cable, due to its fast NVP and reduced need for twist lay variation operates at a <20nS Delay Skew. This is unparalleled by any other Category 5e and 6 UTP cable on the market today. To achieve the Near End Cross Talk (NEXT) performance, all other manufacturers must vary the twist lays greatly, increasing Delay Skew. As illustrated below, it is variation in twist lays which allows for reduced NEXT within cable. Often to increase NEXT performance, Delay Skew must be compromised, “robbing Peter to pay Paul”, so to speak. With the AirES innovation of introducing Air as an insulator the Crosstalk is naturally reduced without increasing twist lay variation. As a function of better insulation through AIR reducing the dielectric constant and capacitive cou- pling, there is less Crosstalk between pairs due to reduced noise. In other words, noise doesn’t travel well through air! The total effect of the cable construction is a smaller cable with better all around electrical performance. In the example below the old version (industry standard design) on the left is compared with the new AirES design. Once jacketed, the effect of having significantly smaller primary conductors carries through to the final overall cable outer diameter. The result is a 28% reduc- tion in cross sectional area for Cat 5e and a 32% reduc- tion for Cat 6. This translates to greatly increased fill rate capacity and easier installation. Note: For more information regarding the mechanical advantages of AirES please see our "Mechanical Attributes" white paper. Quite often in our industry we struggle to understand the relationship between all parameters testing on UTP cables. To break it down into simple terms we are inter- ested in Signal to Noise Ratios (ACR). How strong is the signal when it reaches the receiver and how much noise is on the line. Once again, typically increasing the per- formance of one reduces the performance of the other or the size of the cable must be increased, but not with AirES. The Noise (Cross Talk) has been reduced, not by increased twist rate, but through the introduction of AIR. This allows the twist rates in each pair to be less, resulting in a shorter length on each pair. Ultimately decreasing the amount of Attenuation (Insertion Loss), thus supplying stronger signal strength. Propagation delay is the measured time of the signal from the transmitter to the receiver for each pair. Delay skew is the difference in time between all 4 pairs for the signal to arrive at the receiver Incident Signal V in V out V next V next Attenuated Signal Coupling 0.17” 0.20” TrueNet ® AirES ® Technology: Electrical Characteristics of the Evolution Page 5 Glossary of Terms Reproduced with Permission of Fluke Networks Dielectric Constant: The property of a dielectric which determines the amount of electrostatic energy that can be stored by the material when a given voltage is applied to it. Also called permativity. Length and NVP: Length is defined as the physical or sheath length of the cable. It should correspond to the length derived from the length markings commonly found on the outside jacket of the cable. Physical length is in contrast to electrical or helical length, which is the length of the copper conduc- tors. Physical length will always be slightly less than elec- trical length, due to the twisting of the conductors. To measure length, a test set first measures delay, then uses the cable's nominal velocity of propagation to cal- culate length. Nominal Velocity of Propagation (NVP) refers to the inherent speed of signal travel relative to the speed of light in a vacuum (designated as a lower case c). NVP is expressed as a percentage of c, for example, 72%, or 0.72c. All structured wiring cables will have NVP values in the range of 0.6c to 0.9c. Similarly, if you know the physical length and the delay of a cable you can calculate the NVP. In most instances, length is derived from the shortest electrical length pair in the cable. Because of delay skew, the length of the four pairs often appears slightly different. This is normal and no cause for concern with the exception of significant (over 10%) variances. Results Interpretation The main concern when measuring length is that there is not a lot of cable in any segment. For horizontal structured cabling this means 100 meters. This is because applications have been designed to support a maximum signal propagation delay, and if the link is too long, this delay could be exceeded. Occasionally installers may leave excess cable in the ceiling or wall in anticipation of future needs. While this is okay if it is considered part of the overall run, tightly coiling excess cable can lead to undesirable performance degradation due to additional return loss and near end crosstalk. Troubleshooting Recommendations One of the most common reasons for failing length on a test is that the NVP is set incorrectly. If you are not careful and use the preset cable type it may not match the NVP of the cable under test. In this case, you can have an NVP difference of 10% or more, which trans- lates directly into a length error. In the event the length is only slightly too long, check the NVP and cable type. Assuming the NVP is correct, another cause of excess length is extra cabling looped in the ceiling or walls. Does the link in question meet the anticipated plan? For example, in the case of an airline hanger or warehouse, a remote station may be forced to be over 100 meters from the wiring closet. If this has been planned for, and the intended application supports the excess length, then the link may fail structured wiring standards but still be approved for the application. Some field testers allow customized autotests to be configured that per- mit variances from standard TIA and ISO/CENELEC requirements. Such autotests are useful because they verify the installation meets requirements while allowing for planned variances. Pr opagation Delay: Propagation delay, or delay, is a measure of the time required for a signal to propagate from one end of the circuit to the other. Delay is measured in nanoseconds (nS). Typical delay for category 5e UTP is a bit less than 5 nS per meter (worst case allowed is 5.7 nS/m). A 100 meter cable might have delay as shown below. Delay is the principle reason for a length limitation in LAN cabling. In many networking applications, such as those employing CSMA/CD, there is a maximum delay that can be supported without losing control of communications. Nominal Velocity of Propagation (NVP) on the other hand, is different. NVP refers to the inherent speed of signal travel relative to the speed of light in a vacuum (designated as a lower case c). NVP is expressed as a percentage of c, for example, 72%, or 0.72c. All struc- tured wiring cables will have NVP values in the range of 0.6c to 0.9c. Results Interpretation Delay measurements are relatively straightforward. Most structured wiring standards expect a maximum horizon- tal delay of 570 nS. If design specifications allow, higher delay can be acceptable. Since each pair in the cable has its own unique twist ratio, the delay will vary in each pair. This variance (delay skew, discussed in the next section) should not exceed 50 nS on any link segment up to 100 meters. Standards require all pairs to meet the requirement. It is possible to report just the worst case pair. This will be the pair with the highest propagation delay. Troubleshooting Recommendations Excessive propagation delay can have only one cause: the cable is too long. If you fail propagation delay, check to ensure that the pass/fail criteria match the design specifications. If so, the cable is too long. In many cases, a cable up to 25% too long (125m for TrueNet ® AirES ® Technology: Electrical Characteristics of the Evolution Page 6 Category 5) will still support most LAN applications. However, the installation will fail most structured wiring standards, such as those published by CENELEC, ISO/IEC, and the TIA. In some cases, if the customer insists on the location of the terminal equipment, and an excessive length cannot be avoided, you can verify other cable parameters. If they pass, you can provide information that indicates the cable meets frequency- dependent parameters but is non-compliant with over- all standards due to excessive length. This provides pro- fessional results to the user while placing on them the responsibility for non-compliant cabling. Pr opagation Delay Skew: Propagation Delay Skew (skew) is the difference between the propagation delay on the fastest and slowest pairs in a UTP cable. Some cable construction employ different types of insulation materials on differ- ent pairs. This effect contributes to unique twist ratios per pair and to skew. Skew is important because several high-speed network- ing technologies, notably Gigabit Ethernet, use all four pairs in the cable. If the delay on one or more pairs is significantly different from any other, then signals sent at the same time from one end of the cable may arrive at significantly different times at the receiver. While receivers are designed to accommodate some slight variations in delay, a large skew will make it impossible to recombine the original signal. Results Interpretation Well-constructed and properly installed structured cabling should have a skew less than 50 nanoseconds (nSec) over a 100-meter link. Lower skew is better. Anything under 25 nSec is excellent. Skew between 45 and 50 nanoseconds is marginally acceptable. Troubleshooting Recommendations If the skew is high, provided the intended application is a 2-pair application such as 10Base-T or token ring, the application should still perform. If one pair is much higher or lower in delay than the others, very high skew may result. Examine the delay results for each pair. If one pair exhibits uncharacteristically high or low delay, re-examine the installation. Near End Cr osstalk (NEXT): When a current flows through a wire, an electromag- netic field is created which can interfere with signals on adjacent wires. As frequency increases, this effect becomes stronger. Each pair is twisted because this allows opposing fields in the wire pair to cancel each other. The tighter the twist, the more effective the can- cellation and the higher the data rate supported by the cable. Maintaining this twist ratio is the single most important factor for a successful installation. If wires are not tightly twisted, the result is Near End Crosstalk (NEXT). Most of us have experienced a tele- phone call where we could hear another conversation faintly in the background. This is crosstalk. In fact, the name crosstalk derives from telephony applications where 'talk' came 'across'. In LANs, NEXT occurs when a strong signal on one pair of wires is picked up by an adjacent pair of wires. NEXT is the portion of the trans- mitted signal that is electromagnetically coupled back into the received signal. Results Interpretation Since NEXT is a measure of difference in signal strength between a disturbing pair and a disturbed pair, a larger number (less crosstalk) is more desirable than a smaller number (more crosstalk). Because NEXT varies signifi- cantly with frequency, it is important to measure it across a range of frequencies, typically 1 – 100 MHz. If you look at the NEXT on a 50 meter segment of twisted pair cabling, it has a characteristic "roller coaster going uphill" shape. That is, it varies up and down significant- ly, while generally increasing in magnitude. This is because twisted pair coupling becomes less effective for higher frequencies. The field tester should compare suc- cessive readings across the frequency range against a typical pass/fail line, such as the Class D specification. If the NEXT curve crosses the pass/fail line at any point, then the link does not meet the stated requirement. Since NEXT characteristics are unique to each end of the link, six NEXT results should be obtained at each end. Troubleshooting Recommendations In many cases, excessive crosstalk is due to poorly twist- ed terminations at connection points. All connections should be twisted to within 13 mm of the point of ter- mination according to ANSI/TIA/EIA 568B. An additional note common to all standards is that the amount of untwist should be kept to a minimum. Experience has shown that 13mm does not guarantee a PASS when field testing. Signal to Noise Ratio (ACR): Attenuation to Crosstalk Ratio (ACR) Attenuation to Crosstalk Ratio (ACR) is the difference between NEXT and the attenuation for the pair in the link under test. Due to the effects of attenuation, sig- nals are at their weakest at the receiver end of the link. But this is also where NEXT is the strongest. Signals that survive attenuation must not get lost due to the effects of NEXT. TrueNet ® AirES ® Technology: Electrical Characteristics of the Evolution Page 7 Using PSNEXT and attenuation, Power Sum ACR (PSACR) can also be calculated. PSACR is not required by TIA/EIA 568-B. Some field testers will report it anyway. However, if you desire PSACR you will need to specify it's requirement in the statement of works document. During signal transmission over twisted pair cable, both attenuation and crosstalk are active simultaneously. The combined effect of these two parameters is a very good indicator of the real transmission quality of the link. This combined effect is characterized by the Attenuation-to-Crosstalk Ratio (ACR). ACR is nearly analogous to the definition of signal-to-noise ratio. (ACR excludes the effect of external noise that may impact the signal transmission.) Results Interpretation ACR is an important figure of merit for twisted pair links. It provides a measure of how much 'headroom' is available, or how much stronger the signal is than the background noise. Thus, the greater the ACR, the better. Troubleshooting Recommendations ACR is derived from NEXT and attenuation data. Any steps taken to improve either NEXT or attenuation performance will improve ACR performance. In practice, this usually means troubleshooting for NEXT because the only way to significantly improve attenuation is to shorten the length of the cable. Web Site: www.adc.com From North America, Call Toll Free: 1-800-366-3891 • Outside of North America: +1-952-938-8080 Fax: +1-952-917-3237 • For a listing of ADC’s global sales office locations, please refer to our web site. WHITE PAPER ADC Telecommunications, Inc., P.O. Box 1101, Minneapolis, Minnesota USA 55440-1101 Specifications published here are current as of the date of publication of this document. Because we are continuous- ly improving our products, ADC reserves the right to change specifications without prior notice. At any time, you may verify product specifications by contacting our headquarters office in Minneapolis. ADC Telecommunications, Inc. views its patent portfolio as an important corporate asset and vigorously enforces its patents. Products or features contained herein may be covered by one or more U.S. or foreign patents. An Equal Opportunity Employer 1317032 5/05 Original © 2005 ADC Telecommunications, Inc. All Rights Reserved KRONE ® is a registered trademark of ADC Telecommunications, Inc. . any and all electrical parameters. A full glossary of terms is included for further understanding. TrueNet ® AirES ® Technology Electrical Characteristics. physical and electrical, are improved to provide a "Win Win" situation for both the installer and customer. This white paper will focus on the electrical