White Paper. Crestron 8G DigitalMedia Cable

Transcription

1 White Paper Crestron 8G DigitalMedia Cable

2 Table of contents A Higher Standard Introduction 3 Understanding category cable 4 How we measure cable 6 Network cable analyzer 6 HDBaseT-specific tools 7 Electrostatic discharge testing 8 Setting a higher standard 9 How DigitalMedia 8G cable measures up 11 Network cable analyzer data 12 HDBaseT data 13 ESD performance 14 Conclusion 15 Crestron, the Crestron logo, DigitalMedia and Sonnex are either trademarks or registered trademarks of Crestron Electronics, Inc. in the United States and/or other countries. ipod is a either a trademark or registered trademark of Apple Inc. in the United States and/or other countries. Dolby and the Dolby logo are either trademarks or registered trademarks of Dolby Laboratories in the United States and/or other countries. DTS-HD and the DTS-HD logo are either trademarks or registered trademarks of DTS, Inc. in the United States and/or other countries. HDMI is a either a trademark or registered trademark of HDMI Licensing LLC in the United States and/or other countries. TOSLINK is either a trademark or registered trademark of Toshiba Corporation in the United States and/or other countries. Other trademarks, registered trademarks, and trade names may be used in this document to refer to either the entities claiming the marks and names or their products. Crestron disclaims any proprietary interest in the marks and names of others Crestron Electronics, Inc. 2

3 A Higher Standard Introduction Today s digital AV distribution systems feature cutting edge hardware to route and manage complex high-speed signals. Tremendous consideration is given to the competitive advantages of switchers and their handling of video, audio, and protocols like HDCP and EDID, and rightly so. However, what often gets overlooked is the conduit through which those signals are transported: the cables. Thanks to sophisticated electronics, and especially the HDBaseT standard, selecting a cable that works is easy. However, selecting the right cable can make a tremendous difference to your bottom line. The right cable will perform with bulletproof reliability, in changing environmental circumstances, and offer a path for future upgradability. Crestron DigitalMedia 8G cable offers outstanding performance for today s HDBaseT applications. But more than that, it can stand up to the most challenging installation environments, and its performance far outstrips the needs of today s digital AV, enabling you to upgrade your systems in the future without having to upgrade the infrastructure. 3

4 Understanding category cable The cables most commonly used in today s digital video distribution networks are category cables, as defined by the Telecommunications Industry Association (TIA/EIA). In these applications, the cables consist of four twisted wire pairs, and may be shielded (STP) or unshielded (UTP). There are four basic parameters used to describe the performance of these types of cables. Attenuation (or insertion loss) is the simplest parameter to understand. The attenuation of a cable describes how much electrical energy the signal loses as it passes through the cable from the transmitter to the receiver. In general, a thicker conductor will decrease attenuation. A longer cable will increase attenuation. Transmission line effects and the skin effect cause attenuation to increase as signal frequency increases. Return loss expresses how much of the transmitted signal is reflected back to the transmitter. Reflections are caused by sudden changes in impedance down the cable. In a cable of reasonable quality, return loss problems are rare, and typically the result of poor termination or physical damage to the cable. Attenuation and return loss are expressed in decibels. Smaller values mean less loss, and are therefore indicative of better cable performance. Crosstalk describes a phenomenon where a signal on wire pair A causes electromagnetic radiation which induces a corresponding signal in wire pair B. Since wire pair B has to transmit signals of its own, this induced signal is noise which interferes with the correct data on wire pair B. Keep in mind that the category cables we are interested in are built for full-duplex applications (i.e., Ethernet), which means there are electrical transmitters and receivers together on both ends of the cable. Crosstalk comes in two varieties. Near-end crosstalk (NEXT) describes interference by the near-end transmitter on signals trying to reach the near-end receivers. Far-end crosstalk (FEXT) describes interference by the near-end transmitter on signals trying to reach the far-end receivers. 4

5 A Higher Standard Crosstalk is also expressed in decibels. Somewhat counter-intuitively, the value for crosstalk actually expresses the cable s ability to reject crosstalk. Therefore, a higher value is better. Like attenuation and return loss, crosstalk is frequency-dependent. In simple terms, higher speed signals radiate more energy than lower speed signals, so they will induce more noise in nearby wire pairs. Typically near-end crosstalk is a more critical problem than far-end crosstalk, because the attenuation of the cable causes the transmitted signal to be reduced in amplitude when it reaches the far end, and therefore cause less interference at the far-end receiver. Crosstalk effects must be measured between each combination of wire pairs. For example, a signal is injected on pair 1-2, and crosstalk effects are measured on pairs 3-6, 4-5, and 7-8. Then inject a signal on pair 3-6 and measure the effect on the other three pairs, etc. A single cable s NEXT performance is actually a set of 12 measurements. The two most important parameters (attenuation and NEXT) may be mathematically combined to produce a single value that provides a simple and concise measurement of a cable s overall performance. Attenuation to crosstalk ratio (ACR) is the difference, in decibels, between cable attenuation and NEXT. A positive ACR implies that the strength of the transmitted signal at the end of a cable (after the attenuation) is sufficient to overcome the noise induced by crosstalk (NEXT). ACR is the best single value to express a cable s overall performance characteristics. 5

6 Because attenuation increases with frequency and NEXT (crosstalk rejection) decreases with frequency, each cable has a certain frequency where attenuation overwhelms NEXT, and a signal is no longer recoverable. Below this frequency, ACR is positive (signals can be recovered). Above this frequency, ACR is negative (signals cannot be recovered). This point defines the maximum bandwidth of the cable. How we measure cable Network cable analyzer To collect the most fundamental data about a cable s performance, a network cable analyzer is the right tool. This is an indispensible part of the cable installer s toolkit. In Crestron s DigitalMedia performance laboratory, we use the Fluke Networks model DTX-1800 Cable Analyzer. It is an easy to use handheld instrument capable of performing all the necessary analysis to measure every important aspect of a cable s performance. The DTX-1800 provides all of the four parameters described above attenuation, return loss, NEXT and FEXT. Armed with this data you can verify the performance of any twisted pair cable. The data can even be used to help troubleshoot cables with problems (e.g., from damage or improper termination). 6 Figure 1: Fluke DTX-1800 Network Cable Analyzer

7 A Higher Standard HDBaseT-specific tools Once a cable has been verified with the basic network analyzer tool, it is worth looking into more application-specific techniques for checking performance. In this case, we are interested in having a cable that can manage uncompressed digital audio and video using the HDBaseT transmission standard. The HDBaseT Alliance has created a detailed device certification program to ensure compatibility between HDBaseT devices from different vendors. To help manufacturers prepare for testing, the alliance has published a software tool for pre-certification. This tool exists to help hardware manufacturers prove that their devices work well enough to be certified, before incurring the cost and time of submitting for certification. The same tool can be repurposed to compare the performance of different cables using the same hardware. Figure 2 shows a screen shot of this tool. Figure 2: HDBaseT pre-certification tool interface There are two values provided by this tool that are of most interest. FMAXERR describes the likelihood that a data link (cable) will have a bit error. Values range from 0.9 (0% probability of error) to 5.0 (100% probability of error no link). A value below 2.0 is considered sufficient for HDBaseT certification, and a value above 2.0 is considered a failing link. FMSEERR essentially describes the signal to noise ratio of the data link. A value of -10 db or below is a passing value. Anything above -10 db is considered a failing link by the alliance. Notice that each of these measurements is taken across four channels: A, B, C, and D. Each channel represents one of the four wire pairs in the cable. 7

8 Electrostatic discharge testing Taking the measurement one step further, we perform full electrostatic discharge (ESD) testing on all DigitalMedia hardware and cable systems. ESD is what happens when a door handle delivers a shock to someone wearing wool socks. It can happen when people or animals brush up against electronic devices during cold dry weather. These very short electrical shocks can actually be up to a few thousand volts! ESD testing in the lab also represents the type of interference that occurs when large electrical motors or devices kick back electromagnetic energy into nearby low-voltage wiring. In the worst case, this kind of spike can destroy hardware. In practice, the most common result is an interruption of data the screen goes black. Figure 3: Static discharge gun set to deliver a-4 kilovolt shock to an HDBaseT reference device connected with 8G cable All DigitalMedia equipment and cable is designed to resist interruption from ESD. This type of testing is particularly important because the real-world triggers are unpredictable and often uncontrollable. Sometimes the cable must run right past an air conditioning compressor. Sometimes a receiver might be brushed by a cat full of static electricity after rolling around on the carpet on a dry day. End users and system integrators become extremely frustrated by intermittent and unexplainable video disruptions with no particular pattern. Our test method involves using a purpose-built ESD gun at up to 4 kilovolts and applying large shocks directly to the hardware under test. We record data on how frequently these shocks lead to video drop outs. These experiments have demonstrated that all equipment transmitters, receivers, and the cables themselves may vary drastically in their 8

9 A Higher Standard Setting a higher standard The CAT5e specification was created in 2001 by the Telecommunications Industry Alliance in order to standardize a generic telecommunications cable suitable for commercial building applications where multiple vendors equipment is expected to interoperate. In the telecom world, CAT5e cabling has been used successfully in applications including 1000BASE-T (gigabit Ethernet). The electrical specification for CAT5e cable only requires a certain performance at up to 100 megahertz (MHz). By utilizing all four wire pairs and sophisticated electrical encoding schemes, one gigabit of data can be carried on such a cable, despite this relatively low guaranteed bandwidth. Today s video applications led by Crestron DigitalMedia 8G+ and HDBaseT require far more bandwidth. In order to support eight gigabits per second, similar levels of coding sophistication are employed, but there is simply no getting around the need for more bandwidth from the cable itself. This means performance beyond the 100 MHz guaranteed by the CAT5e specification. 80 Comparing CAT5e and 8G Specifications Attenuation to Crosstalk Ratio (db) !"#$%&%'#()*+# 8G Limit (db),-./0#$%&%'#()*+# CAT5e Limit (db) Signal Frequency (MHz) Figure 4: Graph of the CAT5e ACR specification (red, to 100 MHz) compared to the 8G ACR specification (blue, to 350 MHz) 9

10 The creators of HDBaseT recognized this, but still had to make certain assumptions about the performance of CAT5e above 100 MHz. Although performance is not 100% guaranteed by the specification, it is not the case that performance simply stops at 101 MHz. Specialty transmitters and sophisticated receivers enable HDBaseT technology to work well on virtually any well-made CAT5e. Still, at Crestron, simplifying assumptions aren t a solid enough foundation on which to build the best video products possible. DigitalMedia 8G+ hardware works better than any competitive devices with off-the-shelf CAT5e, but in order to guarantee the highest level of performance possible, we developed our own 8G cable specification, which exceeds the CAT5e spec. The 8G specification is developed specifically to meet the needs of an HDBaseT connection with the highest performance possible. This means there are performance requirements all the way to 350 MHz, the maximum bandwidth used by an HDBaseT transmitter. This is the standard that must be met by any cable we sell as Crestron DigitalMedia 8G cable. On top of the extended bandwidth specification, our 8G specification calls for an extra 5 to 10 decibels of headroom, to help ensure that any 8G-certified cable offers superior performance. Figure XXX shows a chart illustrating the near end cross talk requirements for CAT5e (in red) and the 8G requirement (in blue). Note that the 8G spec extends fully to 350 MHz, while the CAT5e spec only extends to 100 MHz. See the approximately 5 db more headroom offered by the 8G specification. 10

11 A Higher Standard How DigitalMedia 8G cable measures up Network cable analyzer data Figure 5 shows the ACR performance of a 100 meter CAT5e cable purchased from Monoprice.com. Note that there is a colorful line for each of the 12 wire-pair combinations (as described earlier). In order to pass the CAT5e specification, the cable s ACR must never fall below the CAT5e reference limit (the red line) anywhere from 0 to 100 MHz. To pass the 8G specification, the data must never fall below the 8G reference limit (the blue line) anywhere from 0 to 350 MHz. This cable passes CAT5e but fails the 8G spec. You can see that it holds up to 8G specification until 240 MHz, and then it begins to fall below our high standard. This cable does work with Crestron 8G+ hardware and in general without issue. However, there is very little margin for error. 120 Monoprice CAT5e ACR Performance 100 Attenuation to Crosstalk Ratio (db) G 8G Limit Limit (db) (db) CAT5e Limit (db) 1,2-3,6 CAT5e Limit (db) Signal Signal Frequency (MHz) (MHz) Figure 5: Off the shelf CAT5e ACR performance 11

12 Figure 6 shows the same measurements taken on Crestron DigitalMedia 8G cable. You can see significantly more headroom (the distance between the 8G spec blue line and the per-pair data) across the board. Plus, this cable never dips below the 8G performance line at any frequency up to 350 MHz. This is a cable that will perform well in a DM 8G+ system under all circumstances, day after day Attenuation to Crosstalk Ratio (db) G Limit (db) CAT5e Limit (db) Signal Frequency (MHz) Figure 6: DigitalMedia 8G cable ACR performance 12

13 A Higher Standard HDBaseT data Now we put these cables into our real world application carrying an HDBaseT A/V signal. Table 1 shows the comparison of FMAXERR (bit error probability). On average, the 8G cable performance is 28% better than the standard CAT5e. Comparing FMSEERR (signal to noise ratio), we can see an obvious and similar trend. Table 2 shows the FMSEERR comparison. In this dimension, the 8G cable outperforms standard CAT5e by about 16%. FMAXERR (lower is better) Monoprice CAT5e DM8G A B C D Averages G Improvement: 28.4% FMSEERR (lower is better) Monoprice CAT5e DM8G A B C D Averages G Improvement: 15.8% Table 1: Comparison of FMAXERR on HDBaseT performance suite Table 2: Comparison of FMSEERR on HDBaseT performance suite 13

14 ESD performance ESD performance is an area where the DigitalMedia 8G cable particularly shines. Remember that ESD problems are the most difficult to predict, design around, and troubleshoot. The best offense is a good defense, which means a cable that can take ESD hits, protect the system and keep the signal going. Cable (-) 2.5kv (-) 4kv Monoprice 80/100 80% 100/ % Crestron 8G+ 5/100 5% 5/100 5% Belden 10GX12X 11/100 11% 31/100 31% Belden 10GX62X 13/100 13% 34/100 34% Table 3: Comparison of cable stability under ESD strike conditions The results here are dramatic. The unshielded standard CAT5e cable drops video 80% of the time, when hit with a 2.5 kv shock. At 4.0 kv, this cable drops the video 100% of the time! Do you want your client to experience regular mysterious video dropouts? For this experiment we also compared some very high end CAT6A cable from Belden. This cable is an all-around good performer, but even it drops video nearly 1/3 of the time when hit with a 4.0 kv shock. This even goes for the shielded 10GX62X cable. Crestron DM 8G cable is engineered for great performance under simple environmental conditions, but in difficult installs it really shines. Even with a 4.0 kv shock applied directly to the 8G+ hardware, DM 8G cable protects the system and keeps working flawlessly 95% of the time! 14

15 A Higher Standard Conclusion HDBaseT has proved to be a great advancement in state of the art digital video transport. This powerful technology has extended the life of CAT5e already in use for over a decade by years. Being able to send uncompressed 1080P video, reliably, over this inexpensive cable is truly incredible, and DigitalMedia 8G+ is the finest hardware available to take advantage of this technology. When you need to retrofit a building full of CAT5e with the latest and greatest digital video equipment, DigitalMedia is clearly best choice, no matter the cable. But when you get to choose your cable, don t settle for good enough. Select the very best shielded twisted pair digital video cable available choose DigitalMedia 8G cable. Not only will it guarantee a smooth and easy install today, but the extra bandwidth performance it provides will protect you tomorrow, when it s time for 4k, 8k or even higher resolutions. And don t forget about the ESD protection afforded by 8G cable. No matter what signal you are sending, environmental influences can ruin the end user s experience. Choose the cable that protects you during installation, daily usage, and future upgrades. Choose DigitalMedia 8G cable. 15