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                                Other Flours of xDSL


There are number of different categories are available in DSL technology. Principle of transmission is called, DSL or Digital Subscriber Line. Though its digital, it can be provided to customers in different form and varies according to the country and the telecom provider. This is the reason, for small "x" to be in front of the DSL letterings. "x" could be any method used to transmit digital subscriber line to end users.

ADSL,VDSL,SDSL,HSDL,BDSL,ADSL2,VDSL2 are few examples, uses  DSL technology in many shapes to transmit data at different speeds to it's end users. As you can see, the first letter keeps on changing in each and every service category while the last three letters always the same and unchanged.

Each and every service category has it's own method of transmitting data and limitations. I will go through it briefly, to furnish you about different popular xDSL technologies available around the world. 

DSL stands for, Digital Subscriber Line.


Service Name Further Express Transmission   Media Max Data Rate (Approx) Service Limit (Approx) ITU Standard
      ADSL Asymmetric Digital  Subscriber Line   Copper Wire     8-10Mbps   18,000 feet    G.992.1

Asymmetric Digital

Subscriber Line2

  Copper Wire     12Mbps   20,000 feet    G.992.3

Asymmetric Digital

Subscriber Line 2 Plus

  Copper Wire    25Mbps   5,000 feet   G.992.5
    VDSL Very High Data Rate Digital Subscriber Line   Copper + Fiber



  1,000 feet

  4,000 feet

   VDSL2 Very High Data Rate Subscriber Line 2   Copper+ Fiber   100Mbps   250 feet   G.993.2
   SDSL Single Line Digital Subscriber Line  Copper Wire    6Mbps   10,000 feet  
   DSL Digital Subscriber Line Could be Copper or Fiber     Varies   Varies  

Now, here we can clearly see, shorter the distance higher the speed. As you can see, specially in VDSL, service distance is limited to 1000 feet in it's full service. In the sense, 52Mbps can only  cover the customers who live closer to the exchange within the parameter of 1000 feet. But, with the aid of fiber, service providers can reach customers lived beyond the limit of 1000 feet. This is how its been done.  In countries where VDSL is provided, fiber cables are used to reach closer to door step of the customer premises. VDSL is popular in developed countries where most  people lived in a very close proximity buildings and with dense population. High rise housing complexes, apartment buildings are primary target in providing VDSL and VDSL2 services. Usually fiber from the exchange will run up to the centre of the city, rather near to the dense building area with most people live ,and their onward it connected to copper wire and delivered to the customers. The system is called "FTTC" or "fiber to the curb" and some countries uses fiber all the way home and it's been called "FTTH". FTTH is not always possible because, unlike copper, its very costly to deploy and maintain. Likewise xDSL is invented to deliver fast data using inexpensive copper infrastructure. Therefore, fiber media is not a substitute for a copper wires. Providers are compelled to use copper loop at least for last segment of the network up to the customer premises to subsidize the coast involved in delivering of xDSL. Here we can understood that, VDSL connections are only available in countries where fiber networks are well deployed and deployed. This is how VDSL is delivered to the customers lived away from the maximum service limit of 1000 feet from the exchange. And one thing to remember, most of times VDSL is symmetrical. That means, your upload data speed and download data speeds are equal. But when the distances increase, it is not possible to provide symmetric data stream and it become asymmetrical. i.e 55mbps VDSL at 1000 feet is said to be symmetrical while 15Mbps at 4000 feet is asymmetrical. VDSL technology is still not available in Sri Lanka.