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How to prevent noise in high-speed Ethernet networks

Mode Conversion Testing Prevents Your Network from Hanging in the Balance

There is a reason that balanced twisted-pair copper cabling is used for today’s high-speed Ethernet networks, and that reason is balance. Noise immunity is an important factor in the ability of a cable to properly transmit Ethernet signals, and the balance of the two conductors in a twisted pair is what cancels out noise injected into the cable. Balance is also responsible for preventing signal leakage from the cable. As we move to higher frequencies and faster data rates, cables are even more sensitive to noise, and ensuring good balance becomes more vital than ever.

Balance in twisted-pair cables is achieved through the overall design of the cable and precise manufacturing. However, not all cables are the same and there is plenty of variability in the marketplace. Ensuring balance of a twisted pair through mode conversion testing is an excellent indicator of noise immunity, including alien crosstalk (AXT) in higher frequency applications.

However, mode conversation testing is not currently a field test requirement per industry standards due to lack of field test equipment able to perform these tests. Installers and end users in the field have had no means to verify balance—until now.

Why Balance Matters

The basic concept behind balance is that Ethernet signals are applied in differential mode to the two conductors of a pair as opposite positive and negative voltages, otherwise known as out-of-phase. In differential mode, the two signals reference each other. This differs from common mode where the signals appear in-phase and are referenced to ground.

Common mode signals can be partly converted to differential mode along the transmission path of a data link and vice versa.

Referred to as mode conversion, this phenomena can occur within a pair or between pairs, and it’s not a good thing. When noise is injected into a cable in common mode, a percentage of that noise can be converted to differential mode and become part of the Ethernet signal. The imbalance caused by this noise in turn causes the voltage on the balanced pairs to be unequal, degrading the

differential signal of Ethernet transmission with the potential for bit errors, retransmissions and slower network performance. Mode conversion can be particularly problematic in Industrial Ethernet and data center applications where the environment is noisy and latency is critical.

Balance is achieved through the overall design of the cable and precise manufacturing that results in tighter, more consistent pair twists with equal sizing and spacing of the conductors. A well balanced cable offers better noise immunity in that the induced common mode noise will appear as equal or nearly equal voltage on the balanced pair and hence be cancelled out.

 

Figure 1 below demonstrates the difference between a link with good balance and a link with poor balance. In the link with good balance, the injected mode is seen as equal and the differential mode signal remains the same voltage at the other end of the link.

In the link with poor balance, the injected mode is not seen as equal by both conductors, resulting in unequal differential mode voltage at the far end.

 

 

Figure 1 below demonstrates the difference between a link with good balance and a link with poor balance. In the link with good balance, the injected mode is seen as equal and the differential mode signal remains the same voltage at the other end of the link.

In the link with poor balance, the injected mode is not seen as equal by both conductors, resulting in unequal differential mode voltage at the far end.

TCL and ELTCL Mode Conversion Parameters

ANSI/TIA-568-C.2, ANSI/TIA-1005 and ISO/IEC 11801:2010 includes two mode conversion parameters that indicate balance—TCL and TCTL. Transverse Conversion Loss (TCL) is mode conversion measured within a pair at the same end. As shown in Figure 2, it is measured by injecting a differential mode signal into a twisted pair and then measuring the common mode signal returned on that same twisted pair. The smaller the common mode signal returned, the better the balance. TCL seems similar to a Return Loss measurement, except that rather than measuring the common mode signal returned, Return Loss measures the differential signal returned.

Connected to shield if present Connected to shield if present

Figure 2 TCL Testing

 

Transverse Conversion Transfer Loss (TCTL) is mode conversion within a pair measure at the opposite end. As shown in Figure 3, it is measured by injecting a differential mode signal into a twisted pair and then measuring the common mode signal at the other end of the link on that same twisted pair. Since the amount of common mode signal is length dependent, equalization must be

applied to take insertion loss into account. Therefore the more meaningful measurement is Equal Level TCTL (ELTCTL). Similar to TCL, the smaller the common mode signal at the far end, the better the balance.

Just as TCL looks similar to a Return Loss measurement, ELTCTL looks similar to an Insertion Loss measurement. However, Insertion Loss measures the differential mode signal at the far end while ELTCTL measure the common mode signal at the far end (TCTL) and then applies equalization based on Insertion Loss to acquire the ELTCTL measurement.

 

Connected to shield if present Connected to shield if present

Figure 3 ELTCTL Testing

 

While TCL and ELTCTL parameters are excellent indicators of the balance of a twisted-pair cable, neither is currently a field test requirement under ANTI/TIA-568.C.2 standards. This is because most field test equipment has only been capable of differential mode measurements. TCL and ELTCTL testing have therefore been limited to laboratory environments by manufacturers who must ensure good pair balance characteristics to comply with TIA and ISO/IEC industry performance standards.

But let’s face it—not all cables are the same and there is plenty of variability amongst design and manufacturing consistency. Furthermore, balance is something that manufacturers typically comply with only through initial quality testing of their products and not necessarily throughout the ongoing day-to-day manufacturing process, which can experience irregularities.

Because TCL and ELTCTL are important measurements that define a minimum performance for balance and therefore noise immunity, there is a growing interest in these parameters among network owners/operators. Rather than relying solely on manufacturer claims, balance can now be verified in the field with the DSX CableAnalyzer (see sidebar). The DSX is the first field tester capable of both differential mode and common mode measurements to support balance testing via TCL and ELTCTL.

 

 

Striking a Balance with ANEXT

At the higher frequency of 500 MHz required to support 10 Gb/s data rates such as with 10GBASE-T, AXT, the unwanted noise coupling between neighboring cables, becomes the limiting factor in transmission performance. That is why higher performance category 6A cables required to support 10 Gb/s are designed with better pair-to-pair balance to provide improved noise immunity over lower category cables.

In the laboratory environment, cable manufacturers test for AXT by using a six-around-one cabling configuration, which provides the worst-case scenario for a cable surrounded by six disturber cables. While this is fairly straightforward, field testing for AXT is a much more complex process. Rather than testing each cable within a bundle, which would be extremely time consuming, practical field certification involves sampling only a percentage of the total number of links, typically 1% or five links. It is also recommended to test the longest and shortest links in a bundle since those tend to exhibit the highest AXT levels. Despite the sampling method, AXT testing is rarely performed in the field and often not required by manufacturers for certification.

While few have deployed 10 Gb/s speeds outside of the data center environment, 10GBASE-T is expected to make its way into the enterprise space over the next few years. It is therefore becoming more critical than ever to ensure AXT performance. However, the labor costs associated with field testing for AXT are still a concern, especially for large installations with thousands of links. Because much of the previously installed category 6A cabling was not originally tested and certified for AXT, there is no actual way to know if the existing cabling has the AXT performance to support 10GBASE-T.

Luckily balance as determined via testing for TCL and ELTCTL is an excellent indicator of whether or not a cable will provide adequate AXT performance to support 10GBASE-T. Testing for TCL and ELTCTL is a much easier parameter to test for than AXT as it can be accomplished alongside standard field testing for other required in-channel performance parameters (i.e., NEXT, PSNEXT, insertion loss, return loss). In fact, TIA recognizes the strong correlation between balance and noise with TSB-1197, which explains the interaction between balance and mode conversion parameters within a channel and alien crosstalk between channels.

Conclusion

No one can dispute the fact that noise immunity and therefore good AXT performance can be achieved without good balance. With many existing category 6A systems having never been tested for alien crosstalk, and few manufacturers requiring AXT testing, there is no way to know if these installed cables have adequate balance performance to support 10GBASE-T. Testing for TCL and ELTCTL therefore offers significant advantages for both installers and end users.

Whether or not the TCL parameter is eventually required by the standards remains to be seen. While not currently a requirement for compliance with ANSI/TIA-56-C.2, the ability to easily test for TCL and ELTCTL using the DSX CableAnalyzer makes it possible to now verify balance and support for higher speed applications like 10GBASE-T through regular field testing. It’s one of the easiest, most effective ways to ensure that your network performance doesn’t hang in the balance.

What About Balance on Shielded Cabling?

While LAN cabling is predominately unshielded, shielded cabling is often deployed as a means to provide noise immunity in many environments and touted as enabling better performance for high-speed applications. Many argue that alien crosstalk is not a concern with shielded cabling. However, the shield needs to remain continuous throughout the entire channel to ensure good alien crosstalk performance for high speed applications. Balance on shielded cabling tends to be less controlled than unshielded cabling, because the introduction of the screen can reduce coupling of external noise sources to the signal pairs in the cable. While TCL and ELTCTL parameters become less important with shielded cabling, the integrity of the screen itself is critical to the performance of shielded cabling.

An excellent method of ensuring shield integrity is to utilize the shield integrity option on the DSX CableAnalyzer. Shield continuity historically is a direct current (DC) measurement with no distance to fault available. In the data center environment where both ends of the cable reside in racks that are grounded to the building and hence have a common ground, using a DC measurement will show that the shield is connected even when it isn’t. The DSX CableAnalyzer is the first field tester to report distance to shield integrity issues using a patented alternating current (AC) measurement technique, indicating a break in a shield regardless of common ground and pinpointing the exact location of the break.

Testing for TCL and ELTCTL is Fast and Easy with DSX

TCL and ELTCTL is not a field test requirement because until the DSX CableAnalyzer came along, no field test equipment could perform a TCL field test. While the parameter may eventually be required in field testing per industry standards and other test equipment vendors will also eventually offer TCL field measurements, most field testers on the market are normally capable of differential mode measurements only. The DSX CableAnalyzer is capable of both differential mode and common mode, measurements, hence its ability to measure TCL and ELTCTL.

TCL and ELTCTL can be easily added to standard category 5e, 6, 6A or Class D, E or EA testing by selecting the test limit under the folder in DSX called Balance Measurements and looking for the test limit with a suffix of (+TCL) as shown below:

The suffix of (+TCL) indicates a standard ANSI/TIA or ISO/IEC test with the addition of TCL and ELTCTL measurements. ANSI/TIA- 568-C.2 and ISO/IEC 11801:2010 only provide test limits for channel measurements at this time. If you select a permanent link test limit, the TCL and ELTCTL measurements will be performed, but no PASS/FAIL criteria will be applied. Industrial Ethernet standards TIA 1005 with the different E1, E2 and E3 environmental TCL and ELTCTL limits are also provided. Testing for TCL and ELTCTL adds only about 6.6 seconds to the typical DSX AUTOTEST time—a very short amount of time compared to AXT testing and time well spent to verify balance.

 

Source: Fluke Networks  www.flukenetworks.com

 

 

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OptiFiber® Pro OTDR with SmartLoop™ Bi-Directional Averaging

Test fiber right and fast. SmartLoop™ tests two fibers in both directions, and averages the measurements as required by TIA-568.3-D in seconds – without taking the OTDR to the far end. You get accurate, compliant certification in a fraction of the time.

OptiFiber® Pro OTDR

Built for the Enterprise

OptiFiber Pro is the first OTDR built from the ground up for enterprise fiber optic cabling testing. OptiFiber Pro is focused on reducing costs while enhancing productivity and improving network reliability.

  • First OTDR with a smartphone user-interface
  • Industry’s shortest event and attenuation dead zones
  • Accelerate fiber certification with the fastest set-up and trace times
  • SmartLoop™ technology enables the testing of two fibers in a single test eliminating the need to travel to the far end of the connection to perform tests.
  • Versiv™ modular design supports copper certification, fiber optic loss, OTDR testing and fiber end-face inspection
  • Instantaneous bi-directional averaging results included at no charge
  • Improve resource utilization with custom configurations for projects and users
  • Simplify use with “DataCenter OTDR™” mode and EventMap™ view
  • Compatible with Linkware™ Live. Linkware Live enables to easily track job progress, get real-time access to test results to quickly fix problems in the field, and easily transfer and consolidate test results from the tester to LinkWare™ PC Cable Test Management Software.

Source: Fluke Networks www.flukenetworks.com

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Hackers take over a Tesla’s brakes from 12 miles away.

A Chinese hacking collective has released a video purporting to show the first remote hack of a Tesla vehicle, just a day after Elon Musk’s company announced a rollout of new safety features for its Autopilot software.

The hack was carried out by Keen Security Lab and shows the team controlling the brakes from 12 miles away and operating the door, dashboard screen, trunk, sunroof, lights, windshield wipers, wing mirror and chair – the latter being for any nefarious hacker wanting to make a passenger slightly more comfortable, against their will.

The entire series of hacks was carried out using a laptop, either from across a car park, in the passenger seat, or at a location out of view. But key to the hackers’ claim is the fact they were never plugged into the vehicle as has been the case with previously publicized exploits.

The video appears to portray a pretty damning picture of Tesla vulnerabilities, particularly since the team claims its techniques will work on other Tesla models and not just the S P85 and S 75D used in the demonstration. Plus the hacks were carried out in both parking and driving modes.

However, a Tesla spokesperson said that the set of circumstances necessary to enable the Keen hacks were extremely narrow, by the car company’s own estimation at least.

“The issue demonstrated is only triggered when the web browser is used, and also required the car to be physically near to and connected to a malicious Wi-Fi hotspot,” said the spokesperson.

“Our realistic estimate is that the risk to our customers was very low, but this did not stop us from responding quickly.”

Backing this statement up, there is an odd exchange in the video when the Keen driver is asked by his would-be hackers and colleagues to search for a nearby charging station before setting off.

Most importantly, all the security issues demonstrated in the video were fixed by an “over-the-air” software update that was deployed within ten days of Tesla receiving the Keen report.The narrow set of parameters needed for the hack to be possible, combined with the fact it took the Keen team months of research to collectively discover the hacks, suggests there isn’t too much to worry about.

Nevertheless, seeing lab director Samuel Lvlurch forward in the driver’s seat when the brakes are activated remains a troubling visual reminder of just how dangerous these kinds of vulnerabilities obviously are – this is in spite of the fact the car in the Keen demonstration is travelling at low speeds for safety purposes.

The Keen team is made up of professional hackers. Together they won $557,500 of prize money at the Pwn2Own hack contest in 2015 for a series of exploits including a 30-second Adobe Flash hack.

And these are the kinds of groups Tesla actively seeks help from. “We engage with the security research community to test the security of our products so that we can fix potential vulnerabilities before they result in issues for our customers,” continued the spokesperson. “We commend the research team behind today’s demonstration and plan to reward them under our bug bounty program, which was set up to encourage this type of research.”

The Keen Security Lab, for its part, reminds all Tesla owners to make sure their firmware is up to date.

This is far from the first time a Tesla vehicle’s safety has been publicly critiqued.

Following the fatal crash in June involving a semi-autonomous Tesla S, a US-Chinese research team proved that a series of off-the-shelf tools could be used to confuse the vehicle’s autopilot sensors and effectively trick it into thinking an object was in front of it that did not exist, or that a real object was not in fact there.

With the memory of the fatal crash still fresh, Tesla announced September 19 it would roll out an updated version of its Autopilot software (8.0) on September 21. This will include more than 200 new safety features and see the car’s radar become a “primary control sensor.”

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Could This Be the End of Indoor Cellular Dead Spots?

How SpiderCloud Is Changing The Way We Do Indoor Cellular

Connectivity becomes more important every day, as cellular and WiFi-enabled devices become large facets of everyday life and business stops being tethered to a desk or desktop computer. As many advantages as the leaps forward in mobile technology have provided for both businesses and consumers, they have also drawn attention to the increasingly widespread problem that cellular coverage just isn’t keeping up with the demand. Dead zones aren’t just something out of The Walking Dead, they’re a large part of our indoor cellular experience.

Rural areas, sheltered locations and medium to large buildings can be dead zones for cellular coverage. This situation leads to the strange phenomenon of a metropolitan conference center becoming as cut off from the rest of the world as a remote outpost in Antarctica, via lack of cellular coverage. Large scale solutions to combat cellular dead zones can be expensive and difficult to justify for some smaller venues, but the faster mobile technology integrates itself into every aspect of life, the more dead zones become less of an annoyance and more of a serious problem.

SpiderCloud, a California-based startup, has a unique solution to the cellular dead zone problem. They are treating spotty cellular coverage not as one big problem, but as a series of smaller problems all strung together. Using small cells – a catch-all term for discrete, linkable short-range RF transmitters – SpiderCloud is creating an affordable, scalable cellular Distributed Antenna System designed for medium and large enterprises and venues; a system that is both much more affordable and much more effective than any other solution for providing complete cellular coverage to medium and large buildings.

On its own, a single one of SpiderCloud’s small cells isn’t particularly impressive. Each one has an in-building range that is only in the tens of meters, enough to provide coverage to a small-ish room, but useless over large distances. SpiderCloud’s small cells are not, however, designed to be used one at a time. Instead, the small cells are designed to be used in concert, with many small cells linking together to provide networked coverage over a large area. The system is almost infinitely scalable: while a small venue can make do with a small network, a large venue can continue adding small cells to provide powerful and evenly-distributed coverage over the entire venue. Signal strength and dead zones cease to be issues, as individual small cells can be added to the network to add coverage to specific areas in the venue, and the built-in redundancy of a network of small cells means that if a cell breaks or needs maintenance, the loss of coverage to the entire venue is absolutely minimal.

The infinite scalability factor is definitely one of the unique features of SpiderCloud’s Small Cell deployment model, but SpiderCloud has some other game changing features up their sleeve as well. One of SpiderCloud’s most characteristic features is it’s Self Organizing Network (SON). The intelligent SON feature means that their small cell Distributed Antenna Systems have the ability to self configure, self optimize and self heal; this centralized, single point integration means it’s capable of extremely rapid deployments because there is no manual configuration required.

Another reason, and probably the most important reason, SpiderCloud is standing out from other indoor cellular companies is because their technology is capable of using a building’s existing Ethernet infrastructure for connectivity and power. That’s right, add another switch to your IT rack and you’re off and running. No large orders of tens of thousands of feet of half-inch coax cable are required to serve as the horizontal backbone for their small cells, it’s all run on traditional twisted pair cabling (Cat5e or better). Not only does this translate into major time savings, but it also translates into major money savings as well. In fact, SpiderCloud technology boasts up to 10x the capacity of comparable Distributed Antenna Systems at less than half the price. It’s kind of a big deal.

SpiderCloud’s little-startup-that-could mentality is making waves and winning it valuable friends. In the US, SpiderCloud has partnered with Verizon Wireless for cellular coverage over its small cell systems, while in the UK and Europe SpiderCloud is working with Vodafone and other major mobile carriers. On the east coast, installations have begun in Philadelphia and New York, and venues in Boston are next in line to upgrade their wireless coverage with SpiderCloud’s small cell systems. With such effective technology, strong partnerships, and an IPO on the horizon, SpiderCloud could very well change the way medium to large venues handle cellular coverage almost single-handedly. And who’s the east coast telecommunications firm that’s certified in SpiderCloud Small Cell technology? None other than Telecom Infrastructure Corp.

If you’re interested in upgrading the indoor cellular coverage for your building or office space, then don’t wait, call Telecom today and ask about Distributed Antenna Systems and SpiderCloud.

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