Advertisement
Articles
Advertisement

Testing's Inherent Evolution

Sun, 06/30/2002 - 8:00pm
Duffy Hayes, Senior Editor


Alongside the development of today’s increasingly complex HFC networks,
the tools techs rely on for testing and measurement are evolving to include
digital technology, smaller form factors, and greater functionality
as operators migrate to advanced services.

For years, much of the technology used for testing and analysis of cable network performance went relatively unchanged. Headend operators had a select set of testing tools, which mainly served the purpose of troubleshooting video delivery systems in the RF realm, and their toolsets performed relatively simple tasks to ensure quality video delivery.

But today, the cable operator marketplace is in flux, and the future seemingly rests on operators' ability to move beyond simple video transmission. Future fortunes will be made in advanced services, and networks have undergone radical change to meet the perceived demand for high-speed data, video-on-demand, and other new interactive services that require a busier, faster, more complex HFC network.

So, it should come as no surprise that as network performance and reliability become increasingly essential with the introduction of advanced services, tools that maintain a raised level of performance are finding their way into operator headends and technician trucks.

New testing products from the industry's leading toolmakers are trending in similar directions. New testing tools are providing technicians more power, more functionality, and more portability in the field. Advances in chip form factors, and new all-digital signal analysis technologies are making for some incredibly small, yet imminently powerful tools for techs to bring into the field, into their trucks, and even worn on their belts. With network intelligence being distributed further and further out on the network, technicians are increasingly required to perform more complex measurements and analysis while in the field. And testing gear makers are introducing new products to meet that demand.

The other major trend affecting test and measurement in the cable world is dealing with new data traffic, as well as maintaining both the upstream and return paths of the network. The carriage of DOCSIS cable modem traffic presents new performance thresholds that techs must now maintain. And as operators move into more two-way interactive services, tools that maintain the once-neglected return path are in demand more than ever.

The people at test equipment provider Trilithic are trying to wrap their arms around each of these major trends with the introduction of a new modular HFC testing product–the 860DSP Multifunction HFC Analyzer–described by Trilithic Marketing Manager Jim Harris as "a platform that operates as an instrument." The portable tester, weighing in at just 4.5 pounds, provides the basic functionality of a high-performance signal level meter, but adds other measurement capabilities through custom options added to the platform via firmware upgrade. In a sense, the 860DSP alleviates the problem of having to design hardwired changes and introduce entirely new products in order to add new functionality.

"We're trying to rise above the notion that we're building a 'brick' that makes a certain measurement," Harris explains. "We're building something that potentially can contain anything that a technician wants to do that runs on batteries that he can hang from a shoulder strap. But the real issue was to address things we haven't thought of yet."

Harris really means it when he says "anything." For an additional $500, users can add the functionality of a high-performance spectrum analyzer, with a resolution range from 3 MHz down to 10 kHz. QAM analysis is another available option. The 860DSP also can emulate the two popular Trilithic return products–the general purpose SSR for return sweeping and ingress hunting, and the handheld RSVP emulator.

DSP, or digital signal processing, is the technology behind the development of the 860DSP, and was the catalyst to getting the product out of the drawing board phase and into reality, Harris says. For Trilithic, DSP was a way to quickly convert signals into data without spending a lot of money on RF hardware to get that signal turned into large blocks of data. In the 860, Trilithic digitizes the band in 8 MHz blocks, and strings them along like beads. Each "bead" in the string gets digitally crunched down to spans of 10 kHz from there.

8600SP
Trilithic’s 860DSP
Similar DSP technology is the brains of a new digital service activation meter from Acterna–the DSAM-2500. The full-service signal level meter is aimed at operators who are deploying new high-speed cable modem services. It adds DSP and DOCSIS/Euro-DOCSIS chipset technology to enable communication between the meter and a network's CMTS, and features a "ruggedized" package that can withstand torrential rain or a four-foot high drop.

In terms of functionality, software options to the DSAM-2500 can increase the meter's capacity, and other features include a one-button Auto Test feature that ensures digital, analog and DOCSIS tests are conducted the same way by all technicians, from grizzled veteran field techs down to novices new to the job. Test results can also be archived for later analysis, and the meter itself includes more than 100 pages of on-board context-sensitive help pages in four languages.

A recent addition to the line of service meters from Sunrise Telecom–the CM500IP Installer Profiler–also aims to provide techs (from expert to novice) the ability to qualify signal paths for new high-speed data services, though not in a DSP environment. It also communicates with a network CMTS via non-intrusive in-band signals, and adds one-button automated functionality called SMART (Selectable Measurement Automated Routine Tests).

Sniffer Shadow
ComSonics’ Sniffer Shadow
Sunrise's CM500IP also provides both analog and digital measurements, switching between analog and digital mode to measure QAM as well as common digital signal impairments. An additional Sub Band option provides an upstream spectrum display and the capability of measuring bursty TDMA upstream signals, ingress, noise and common path distortion. It also is small, rugged and battery-operated, like many of the new handheld digital meters hitting the market today.

Following the trend of giving technicians more portable, and yet more powerful tools for the field, come new products developed for use with the many handheld PCs out there. One product from Pangrac & Associates, called the Tech Assistant, aims to enable these types of handhelds for installers. The software platform provides a way for technicians to store a wide assortment of system information on their handheld PCs, including more than 1,000 miles of system maps. It also has embedded software to automatically calculate things like C/N specifications and return path loss, among others. Guides for troubleshooting and test instrument procedures are also included to enable handhelds with more auto capabilities than previously available to technicians. Pangrac is also working on coupling its Tech Communicator cable plant voice/data radio with the Tech Assistant, which will bring even more functionality to installer handhelds in the future.

SLM 1453
Sencore’s new SLM 1453
In terms of specific testing technologies for DOCSIS rollouts, Agilent Technologies has introduced a testing platform specific to analysis of both upstream and downstream DOCSIS signals. The new Agilent E7333A DOCSIS Protocol Analyzer (DPA) enables truly advanced visibility into DOCSIS protocol implementations, by first acquiring the DOCSIS network signal and then decoding MAC messages within a dynamic RF range. A triggering subsystem provides needed physical layer measurements, and has up to 16 MB of downstream and 8 MB of upstream acquisition memory. The new DPA currently supports DOCSIS 1.0 and 1.1 specifications, with planned support for Euro-DOCSIS in future iterations of the system.

Return path clean-up… Looking for leakage

As noted earlier, the nature of cable network traffic is changing as new advanced services are rolled out. As networks evolve, so too must the instrumentation that keeps networks operating at a new reliability threshold.

MTS300 MPEG Test System
The MTS300 MPEG Test System from Tektronix
As operators carry more data traffic (ostensibly under the DOCSIS protocol), the health of the once neglected return path becomes much more critical. Clean upstream plant means higher reliability, and as operators begin their migration to the DOCSIS 2.0 protocol, they'll be motivated to clean up both sides of their plant, and drop noise levels by at least 6 dB. By simply paying more attention to noise in the upstream channel, operators can potentially move twice the data traffic as they would over a dirty upstream channel.

Specifically, network technicians are increasingly testing for signal leakage more and more in their return paths; enabling fast two-way data services requires that network operators get a handle on the problems of ingress and signal leakage along the return path.

DSAM-2500
Acterna’s DSAM-2500
"The key to advanced services is, if you connect a potential customer without verifying what's coming out of that home, they can inject enough problems back in the return path to kill all of your other subscribers," explains Bret Harrison, customer services manager with testing provider ComSonics.

This is the idea behind a new near-field leakage detector from ComSonics, a premises tool for "sniffing" out signal leakage. Called the Sniffer Shadow, it offers unique dual-mode operation for both monitoring, and the consequent measuring, of RF leakage along the plant. The cell phone-sized detector works off of Lithium batteries, and in its "active sleep" Monitoring mode, can run detection tests for more than 100 hours. When leakage is detected, the technician flips up the LCD cover to reveal an integrated antenna to measure the leakage in microvolts per meter. Readings also feature "leakage validation," which tells whether the signal being measured is electrical noise or true RF leakage. This feature bypasses some of the transmitted "tagging" required by other leakage identification systems, and keeps monitoring and measurement functionality in one small, powerful unit.

A new digital signal level meter from Sencore– the new SLM1453–also addresses leakage in its new design. Sencore has added leakage monitoring and measurement to the meter's basic digital level functionality, and has made leakage detection a simple task for even the greenest field techs. The new SLM1453 also has two antennas: one to monitor and gauge the direction of the leakage, and a second dipole antenna for measurement tasks. Because it doesn't employ any sort of tagging method for signal tracking, the new Sencore meter can't distinguish between true RF leakage and other types of noise in the plant. However, it can work with other tagging systems by tuning in any frequencies set up for tagging by technicians. Battery life is a bit less than with the Sniffer; the Sencore meter operates for 14 hours when charged, but can operate off of a vehicle's battery for non-battery operation.

New platforms for leakage analysis are being looked at more closely as well. At Cable Leakage Technologies, its Wavetracker platform adds a geographical component to the hunt for signal leakage. By utilizing standard GPS technology, the dual-antenna Wavetracker not only listens for RF, but assigns a positioning fix via satellite every second. With the combined functionality, a technician can fully automate the process. Point files are collected to tell exactly what the amplitude of a signal is, on a certain street, at a certain time, in front of a certain house. Analysis software the company calls APLAS (Automatic Positional Leakage Analysis) looks at the leaks in a relative environment, peaks them out, assigns a street address and signal amplitude, assigns a repair and cost code, does pass-fail calculations, and then writes up a work order. APLAS even creates the required FCC CLI Form 320 from collected information, which for years was the only reason to measure cable leakage. Today, it's a more important measurement in achieving overall network health.

"Originally, (measuring for leakage) was a 'have-to' kind of thing. It was a mandate from the government," says Perry Havens, owner/operator of CLT. "Now it's a proactive issue with regard to customer service and signal integrity."

Tempo Research has included some leakage detection capabilities in its line of analyzers and fault locators. Specifically, Tempo's SignalScout RFM151 helps technicians do troubleshooting and maintenance anywhere in the network. It provides requisite signal level measurement tasks, and adds spectrum analysis, ingress and digital channel RF measurement as part of the package.

Another result of increased data carriage is a byproduct called "group delay," a situation similar to chromatic dispersion in the fiber optic world. When an operator sends digital data, there will be a certain level of linear distortion and a difference in delay when the frequencies get to their destination points at different times. The result is intersymbol interference, or ISI, which can wreak havoc on digital data.

To combat the problem, a small testing company called Holtzman Inc. has developed a system employing DSP to measure for the presence of group delay without having to take the plant out of service. A technician sets up a black box transmitter to a tap, fires a signal upstream, where it is captured by a digital oscilloscope, downloaded to a PC and then analyzed. It's a system operators heretofore have overlooked, but with more DOCSIS rollouts nationwide, group delay is creeping into lots of networks.

Cable leakage, intersymbol interference, group delay, ingress, noise…When will it all end? Unfortunately, never, but with the right sets of tools and measurement platforms, operators can get a needed grip on their afflicted networks. It's an easy way of getting ahead of the increasingly important customer service curve.

 

Raised consciousness for audio

In legacy cable networks, audio integrity was an issue in the back of operators' minds…way back.

The new LM100 Loudness Meter

But as cable content moves over to the digital tier, and more cable customers are hooking hi-fidelity home theater systems and Dolby 5.1 audio decoding products into their set-top systems, audio testing has grown more important than ever.

Channel loudness and loudness deviation from program to program are areas of keen concern. In legacy cable networks, operators either disregarded loudness variance, or attempted to measure it using arcane methods like relying on an overdeviation indicator.

DM100 Bitstream Analyzer
Dolby’s DM100 Bitstream Analyzer
Audio technology leader Dolby Laboratories has developed a product–the LM100 Loudness Meter–to help operators deal with some of these loudness issues. By utilizing a standardized measurement algorithm, the meter returns a numerical value (rather than a bouncing needle that must be interpreted) which can then be compared to the dialog normalization level sent along in the metadata of the AC3 audio stream.

"Up until now, the headend has had no way of objectively investigating (loudness complaints) because it was all hearsay," explains Jeff Riedmiller, a senior engineer for digital cable and satellite at Dolby. "With the LM100 being able to look at that digital AC3 bitstream, it can measure it and compare it to the incoming dialog value to see if they are valid."

In addition, the LM100 has a mechanism to time-stamp and date all of these measurements, creating a log that can be used to pinpoint the problem for unknowing programmers.

For basic audio bitstream analysis, Dolby offers the DM100 Bitstream Analyzer, a handheld tool for either the headend or field that does signal analysis, emulation, error logging and stream format investigation.

Video testing and new interactive services

The migration to the digital tier and greater reliance upon the MPEG compression standard means that the scope and complexity of video testing is evolving within an operator's network. Specifically, if operators are looking ahead to interactive TV services (which essentially mix video and two-way data), MPEG testing is more relevant than ever, as data streams must consistently be checked as they move through the distribution chain.

To meet these new MPEG demands, Tektronix is introducing a suite of advanced interactive test tools to its MTS300 MPEG Test System to help guide network operators through new MPEG testing complexities.

The first addition, a carousel analyzer, has a direct impact on new iTV services in that it can enable technicians to quickly analyze a protocol stack's many layers. That should go a long way in reducing some of the inherent complexity of today's new iTV platforms. Also new is an elementary stream analyzer, which tests the lower levels of an elementary stream within a transport multiplexer in order to verify encoder performance at the most basic levels. Finally, Tektronix has added an offline multiplexer to the test set, a tool that can produce multiple transport streams to methodically test performance, from broadcast facilities down to associated consumer devices.

Topics

Advertisement

Share This Story

X
You may login with either your assigned username or your e-mail address.
The password field is case sensitive.
Loading