Sep 17 2012
By Fred Hoot - Google+
Broadband Expert writers were ridiculed when they first wrote about DSL lines. The beginners guide on Getting your first DSL line received a lot of attention and laughter from the high-tech community as the idea of anyone choosing DSL was akin to using an abacus to solve calculus problems instead of a computer.
That being said, DSL is the most widely used high-speed Internet access medium in use today. Plain old DSL is relatively slow, but improved technologies such as ADSL, VDSL, ADSL2+ and VDSL2 make DSL service faster, more reliable and more desirable over regular DSL.
ADSL or Asymmetric Digital Subscriber Line is a higher speed of DSL service. ADSL equipment can provide download speeds of 8 Mbps to 10 Mbps as compared to a max of 3 Mbps for common variety of DSL services. ADSL is a vast improvement over regular DSL.
VDSL or Very high speed DSL can offer speeds of up to 52 Mbps. This 5X gain seems impressive, but there are even better DSL services available. VDSL2 typically provides of up to 100 Mbps. Yes, theoretically 300 Mbps is possible, but you would have to live right next to the CO (Central Office) with a direct line to achieve such a speed.
You can now take the DSL service and apply several different technologies to further increase the access speed for Internet use. Some of the most popular are bonding, Phantom DSL, Vectoring and Dynamic Spectrum Management.
Bonding is the combining of two or more circuits to provide a higher-speed Internet connection that is available with a single circuit. The concept is not all that new.
Back in 1997, FatPipe was one of the early companies that offered commercial products primarily for businesses that needed higher speeds than T1 or T3 circuits could provide. Their equipment was rarely used for the lower speed DSL applications.
You can also bond circuits yourself. Broadband Expert wrote about bonding two 150 Mbps FiOS circuits to create a 300 Mbps ultra-high speed Internet connection. You could order multiple DSL circuits and bond them yourself, however, for most people it’s best to let your ISP or telco do it for you.
CenturyLink will soon be offering bonded circuits with up to speeds of 100 Mbps. They are doing this by bonding two or more VDSL2 circuits together.
There is commercial equipment designed for telcos that can bond up to eight VDSL2 circuits together. Consumer-grade bonding equipment is available for two to four DSL lines.
Nokia Siemens Networks explored various ways of increasing the speeds of data over the existing copper lines. They saw that new fiber rollouts were exceedingly expensive and in some cases not feasible due to terrain.
In 2010 Nokia Siemens announced that had achieved speeds up to 825 Mbps over a 400 meter segment of copper cable and 750 Mbps over 500 meter copper transmission lines using Phantom DSL technology.
Nokia’s Phantom DSL technology creates another virtual DSL circuit over top of the existing DSL channel. This can result in a 50% to 75% increase in speeds over VDSL2.
Vectoring is a technology that reduces noise on a circuit. Copper transmission lines are highly susceptible to noise and cross-talk (signals from adjacent copper pairs). Vectoring applies an electronic treatment to the copper transmission lines that cancels out the noise.
This is similar to how jet engine noise is reduced. They inject another noise that cancels out the existing interference, effectively eliminating the electronic noise.
This noise cancellation allows the VDSL2 equipment to operate at optimal speeds, as it does not have to contend with the extraneous signals. To be the most effective, all copper pairs in a cable bundle have to have the vectoring technology applied.
The Alcatel Lucent Corporation developed this proprietary vectoring.
DSM (Dynamic Spectrum Management)
DSM was actually first devised in 1874 by Leon Walres to analyze the consumer goods marketplace. In other words, DSM is Supply and Demand for the DSL lines.
Basically, there is a set of limited data resources available, including bandwidth and power on DSL lines. In 2008, a presentation by Tom Luo at Stanford University discovered that two-thirds of an allocated spectrum is not in use at any specific point in time.
Boiled down, DSM basically re-allocates unused portions of the spectrum and uses those pieces to increase the DSL speed where it is needed. The formulas used are quite intense.
A description of Stanford’s DSM Project by Professor John Cioffi can help you understand what is done “behind the curtain” in Dynamic Spectrum Management.
DSL speed has been increasing. It seems when the maximum speed that could be achieved is reached, a new technology is developed to further increase the maximum possible throughput. No one knows what the real maximum speed attainable could be, so we will most likely see further developments in DSL growth.
Circle Fred on Google+
Follow Broadband Expert on Twitter
Circle Broadband Expert on Google+