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SELT is primarily used for proactive loop pre-qualification. By knowing in advance if a loop is capable of supporting ADSL2+, loop conditions can be fixed prior to rolling a truck to the customer premise.
DELT is primarily used for reactive tests on a loop after a modem has been deployed—either to help troubleshoot a line or to capture a baseline of loop characteristics at the time of installation.
Loop Testing with SELT & DELT
Integrated loop testing lowers your operational costs
The integration of loop test capability into ADSL2+ IP DSLAMs and BLCs, as well as ADSL2+ CPEs, is one of the many ways in which Zhone is helping to lower the operational costs of our customers -- the same basic underlying goal of all Zhone products and services: to provide the products, tools and services needed to lower the Operational Expenses (OPEX) of carriers, service providers, and PTTs.
SELT and DELT achieve this goal by reducing the time and money required to deploy new ADSL2+lines, as well as increasing the efficiency of post-install troubleshooting and maintenance. SELT and DELT are two very different yet inter-related features. SELT, or Single End Loop Test, is a feature present in Zhone ADSL2+ DSLAMs or BLC. SELT is, as its name suggests, a single-ended test—meaning that a copper loop is tested from the DSLAM or BLC only, without the need for any external test equipment in either the CO or at the remote end of the loop.
DELT, or Dual End Loop Test, is a feature that is present in both Zhone ADSL2+ DSLAMs and BLCs, but is also a feature of Zhone ADSL2+ CPEs. Because DELT is a dual-ended test, it requires equipment that supports the DELT feature at both ends of the copper loop. While this prevents DELT from being used on loops where no CPE has yet been deployed, DELT in turn offers a deeper set of loop tests, and can provide very valuable information on the condition of a copper loop.
Frequently Asked Questions
What does SELT mean and what does it do?
SELT stands for Single End Loop Test, and is used to PROACTIVELY test a copper loop when there is no equipment installed at the far end (i.e., there is no CPE installed at the customer's home). SELT allows for basic loop pre-qualification, saving time when deploying DSL to a new subscriber.
What can SELT determine?
SELT can currently determine the copper gauge, the length of the loop, the presence of noise and attenuation of the line, in essence the quality of the copper and its ability to deliver service.
Does SELT require an external test unit?
No, the benefit of SELT is that it is a feature of the ADSL2+ line card, and does not require any external test equipment. This can save significant equipment costs by minimizing or eliminating the need for expensive test equipment.
Does SELT require Zhone's CPE as well?
No, SELT does not require any CPE at all - it is a special feature of the ADSL2+ line card and is designed for use on copper lines where the modem has not yet been installed.
How can an ADSL2+ line card test a copper loop when there is nothing at the other end?
SELT uses a series of advanced features of the ADSL2+ chipset to generate and interpret line reflections.
What is DELT and what does it do?
DELT stands for Dual End Loop Test. Unlike SELT, which tests an un-terminated copper line from the ADSL2+ line card, DELT uses both the line card and a remotely deployed ADSL2+ CPE to perform REACTIVE loop tests in both directions. This allows for much a much finer degree of loop analysis than SELT alone.
What can DELT Determine?
DELT can determine the ADSL2+ data rate (up/down), loop attenuation (up/down), SNR (up/down), and (noise up/down).
If DELT is better, why use SELT?
DELT does provide more information than SELT, but DELT requires a compatible modem at the other end of the loop, meaning it can only be used after a CPE has been installed in the field making it an extremely powerful diagnostic tool. SELT does not require a CPE, which makes it a very unique pre-qualification tool.
Does DELT only work between Zhone ADSL2+ line cards and Zhone ADSL2+ CPE?
No, DELT is an industry specification that is supported by the ADSL2+ chipset vendors. Therefore, Zhone's ADSL2+ line cards can perform DELT tests with any ADSL2+ CPE that also supports DELT. Likewise, Zhone's ADSL2+ CPE can participate in DELT tests initiated from third-party DSLAMs or BLCs that support DELT. However, Zhone is an industry leader in deploying this technology. Please check with your equipment vendor to determine the test capability of third party devices.
Zhone's Single Line Multi-Service architecture (SLMS™), allows carriers to concurrently deliver voice, new premium data and video services over copper or fiber access lines.
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