Single-ended loop testing accelerates the construction and growth of DSL lines

As users flock to high-speed broadband lines, the DSL market is growing at a rapid pace; operators around the world are working hard to meet this demand, especially as they must think hard about how to provide and maintain DSL lines in the most cost-effective way.

In most cases, customer-installed DSL lines are the exception rather than the norm; expensive on-site installation services are common when DSL lines are offered to customers, but most carriers cannot verify the data rates that new DSL customers will receive without sending personnel out. If the market is to continue to grow and if carriers are to maximize profits, they must find new ways to install and service lines at a lower cost.

This is where single-ended loop testing ( SELT ) can come in handy. Just like the metallic loop tester used in the POTS world, single-ended loop testing is an automated testing technique that can test a DSL line from either end, such as the central office or the customer end, although the latter is less common. Double-ended loop testing is also a test method, but it requires a technician, usually an engineer from the operator, to personally go to the customer end of the line to install a DSL modem or some kind of test instrument; single-ended loop testing is completely different. The operator does not need to send a technician to the user's location, nor does it need to install any test equipment at the customer end. In addition, with the standardization of single-ended loop testing, not only can the installation process be more innovative, but the telecommunications operator can also have a more stable and objective basis for comparing the products provided by DSL equipment manufacturers.

Scientists at KPN Research said that operators currently need a method that allows them to efficiently make line inspections part of daily operations. The inspection method of connecting dedicated hardware to the line requires a high cost and is therefore not attractive. However, if the xDSL chip can provide performance parameters to the management system in a stable, consistent and efficient manner, the system can read the performance parameters of all established lines regularly (for example, once a month) and use these actual measured values ​​to build a database. When a potential new customer also requires DSL service, the operator can easily decide whether to provide him with service. "

Why single-ended loop testing?

From applying for a DSL line to installing it, operators are working hard to improve the way they communicate with customers throughout the process, with the goal of providing a perfect first impression and delivering the promised services to customers until the end of the process. Like any customer service relationship, improving the installation and activation process of DSL lines requires providing customers with real and useful information and then providing the best support for this information; unfortunately, DSL operators and telecom manufacturers do not necessarily have the appropriate information about the physical network, so their confidence is not so firm when making promises.

Many of these lines were installed decades ago and have undergone many changes over that long period of time, and the entire process may or may not be documented. Regardless of whether the documentation is complete or not, smart operators will want to actually test the lines to make sure they meet the requirements before writing a certain level of DSL service into their contracts with customers.

For example, many carriers base their DSL service pricing structure on the data rates they promise to customers. However, before they can ensure that new customers will get the service level (bit rate) they require, carriers must learn more about the line conditions at the customer's location, because the quality and performance level of the DSL line will be greatly affected by the customer's local line. The carriers want to know: the length of the line, whether it is a mixed-gauge line, whether there are bridges branching off the line, where these bridges are located, whether the line contains a load coil, and many other related parameters.

Without single-ended loop testing, the only alternative for operators is to send a technician to the user's site to perform a series of measurements; with single-ended loop testing, many operating parameters of the line can be directly derived.

How does single-ended loop testing work?

The DSL chipset included in the client modem or the central office DSLAM can actively perform line measurements, and the measurement items cover all the contents of the G.selt standard. The measured data will be passed to higher levels for analysis. The operator can use this information to judge the line quality according to the predetermined criteria. The single-ended loop test standard may include many measurement techniques, the following are just some of them:

• Time-domain reflectometry
• Frequency-domain reflectometry
• Loop impedance
• Loop capacitance
• Line noise power spectrum

In addition to developing standards for single-ended loop testing and the precise measurements it must perform, another alternative is to use G.selt files and only define the parameters that the modem passes to the higher logic layers. This allows manufacturers to protect their proprietary information, including sampling rates and filter response times of the modem or DSLAM analog front end. [page]

Figure 1 shows the layered structure of a single-ended loop test procedure, which allows the measurement or operating parameters to be completely unaffected by the higher levels in the architecture, but only passes the measured data to them, which is processed by the analysis engine and finally provided to the operator in a usable format. When developing single-ended loop test standards, the interfaces between the various logical layers can be specified in these standards, allowing manufacturers to freely develop new functions and design the analysis engines and user interfaces they need.

Why is there a need to develop a single-ended loop test standard?

The development of the G.selt standard will inevitably bring certain benefits to operators, because even if DSLAMs and DSL modems from different manufacturers are used, the loop test environment does not need to be changed, which makes it easier for operators to integrate DSL equipment from multiple manufacturers into a heterogeneous environment. In addition, any standard that adopts a hierarchical architecture can provide equipment manufacturers with the necessary flexibility, allowing manufacturers to only develop specific layers they intend to provide, use external equipment to implement a certain layer, or even combine or collapse multiple layers together. By specifying interfaces between each layer, manufacturers can develop their own unique analysis engines; in addition, the G.selt standard can also promote compatible and consistent testing technologies in the industry, making it easier for operators to switch from a certain manufacturer's DSLAM or DSL modem to another manufacturer's platform.

SBCTRI senior technical experts said that in order to maximize the benefits of single-ended loop testing, the measurement procedures must be standardized to ensure that any equipment manufacturer can obtain the same measurement results. KPNResearch experts also said that the interface between the chip and the management system must be standardized so that the external software system can read the data and use the data to build a database. In addition, standardization also makes the measurement method independent of technology. Manufacturers can collect the data obtained by the ADSL chip measuring a certain loop, and then use this data to determine whether another loop supports SDSL services.

Although single-ended loop testing has some advantages, the standard-setting process is difficult and takes a long time. The International Telecommunication Union (ITU) recently agreed to start the process of developing a standard for single-ended loop testing. The former editor of G.hs has also been appointed as the editor of G.selt. Any suggestions are welcome and will be used to define the detailed scope and direction of this standard.

The standardization and application of single-ended loop testing will drive the continued growth of the DSL market; in the long run, it can also meet the needs of the growing number of users, thereby helping operators to provide various services at a lower cost.

TLK2208BTLK2226Number
of channels 86Parallel
interfaceDDR-TBIRTBIR/RGMIISerialVMLVMLNumber
of
pins 289196PackageBGABGAPackage
size19
×19cm15×15cm
Total power consumption1.2W1W