Home Telecoms & NBN NBN Co plan to use DLM likened to 'putting lipstick on a pig'

NBN Co plan to use DLM likened to 'putting lipstick on a pig'

Plans by the company rolling out the national broadband network to implement dynamic line management on its fibre-to-the-node and fibre-to-the-basement connections in early 2018 have been termed as something akin to putting lipstick on a pig by the former chief executive of NBN Co, Mike Quigley.

The move has also earned criticism from RMIT network engineering professor Mark Gregory and the Labor Party's shadow communications spokesperson, Michelle Rowland.

NBN Co has outlined plans to use the technology which is meant to stabilise a connection but often results in much lower speeds.

Quigley said the company's plan to use DLM was not surprising. "For as long as they are trying to make the best of an old, unreliable and unpredictable copper transmission medium, they are going to be struggling to provide consistent and reliable high-speed broadband services to all NBN subscribers," he told iTWire in response to a query.

"DLM is another layer of complexity added to DSL technologies that tries, in part, to compensate for other enhancements, such as vectoring, which is deployed to increase speeds. Each time a layer of technology is added, the costs increase. It is hard not to end up chasing your tail when you attempt to compete with fibre using DSL/vectoring on old copper."

big pig

He said this was clear in Nokia's White paper "Dynamic line management combined with DSL innovations".

"They say: 'Service providers invest in vectored technologies so they can offer higher bandwidth. Vectoring cancels crosstalk, reducing the noise level, enhancing the SNR and allowing a higher bitrate. A side effect of noise cancellation is to make the link more sensitive to environmental noise and electromagnetic interference. The presence of repetitive impulse noise or patterns of varying alien noise become obvious, affecting the stability of the DSL and degrading its quality. Using CIRC and G.inp error compensation/retransmission mechanisms help to improve service quality by reducing or compensating for errors. However, transient loss of throughput can be introduced because of excessive retransmissions, affecting, for example, a video stream. Excessive amounts of correction or interleaving are usually also not desired because they can constantly affect the speed and add latency'."

The Nokia paper adds: "The combination of DLM and DSL innovations provides subscribers with proactive maintenance that makes the best use of each DSL and maintains high quality and reliability. Continuous assessment of service quality ensures that if reconfigurations do not provide the required service quality and reliability, the service provider will be notified, and can provide field intervention.”

And, Quigley said, "One can’t help but be reminded of that old expression about lipstick and a pig!"

Asked for his reaction to the NBN Co move, Gregory told iTWire that "dynamic line management monitors consumer VDSL2 connections for signs of instability and, if instability is identified, then the connection speed is reduced (e.g. by reducing the number of higher frequencies used) to restore the line stability."

He said DLM was independent of the transmission technology, in this case VDSL2, and sought to gracefully degrade a consumer connection, rather than have the line drop out due to the VDSL2 configured line being unable to handle the instantaneous errors caused by noise or other impairment.

"Dynamic line management is commonly used with xDSL connections today around the world and it is surprising that NBN Co has taken so long to introduce a dynamic line management system," Gregory said.

"The current lack of DLM highlights that NBN Co has been forced to act as a result of increasing criticism of the obsolete FttN that it is rolling out. The end result is yet another cost blow-out for NBN Co because of the decision to adopt the obsolete copper-based FttN."

Rowland said in a statement that many Australians were well aware of the experience of DLM from the "dreaded" days of the ADSL2 "stability profile".

"This occurs when a copper-based connection becomes so unreliable that speeds are slowed down through a signal profile change in order to stem Internet dropouts," she said. "Consumer forums in Australia have reported instances where ADSL speeds dropped from 21Mbps to 6.1Mbps after DLM was implemented on a copper line."

Rowland said it was very disappointing that some consumers and small businesses would be forced to choose between slow speeds or dropouts over the copper NBN. "This is the second-rate future (Prime Minister) Malcolm Turnbull is imposing on Australians through his flawed engineering decisions".

"Labor’s first-rate fibre NBN would have avoided these trade-offs by delivering faster and more reliable broadband," she added. "More than ever, the copper NBN has become a defining symbol for Malcolm Turnbull’s unstable and backwards-looking government."


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Sam Varghese

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A professional journalist with decades of experience, Sam for nine years used DOS and then Windows, which led him to start experimenting with GNU/Linux in 1998. Since then he has written widely about the use of both free and open source software, and the people behind the code. His personal blog is titled Irregular Expression.