DSL General Information

DSL (Also known as xDSL) is a group of technologies, that provide data transmission through the wires of your local phone company. Previously, DSL stood for digital subscriber loop, although many now have adopted the term digital subscriber line.

With a large variety of DSL services; theoretical downstream speeds can range from 256kbit/s, to 24Mbit/s (24,000 kbit/s), depending on various factors, such as line quality, type of DSL and distance from provider. The most popular version of DSL, ADSL. This is the DSL marketed for the home user due to its low price.
         




DSL Pros and Cons

Pros

• With a ADSL service, you're able to use your DSL service, and the phone line for regular voice calls, at the same time.
• The speed is much, faster than a standard 56k service.
• DSL doesn't necessarily require you drill more holes into your walls. It can often be used on the same phone line, you already have.
• The company that offers DSL service, usually provides the modem as part of the installation.
• It's fairly easy to install yourself.
• Cheaper than many other internet services, such as T1.
• Not sharing your network with your neighbors, unlike services such as cable.
  

Cons

• DSL connection speeds are dependent on how far you are from the provider's central office, the closer you are, the faster your connection is.
• With ADSL, your connection is faster for receiving data, rather than sending it. Although, the average internet user will receive more data than sent. Services such as SDSL, will offer much faster uploading (sending) speeds, but due to the price is generally targeted to small and medium sized businesses.
  
• The service is not always available everywhere. Most local phone companies will provide a DSL service, unfortunately some are unable.

History of Digital Subscriber Line

Digital subscriber line technology was developed by Joe Lechleider at Bellcore (later renamed Telcordia Technologies). The first type of DSL, ADSL (Asymmetric Digital Subscriber Line) was created in 1988, through placing digital signals above the baseband analog voice signal used to carry out phone conversations.

US phone companies will promote DSL to compete with cable internet service. The first DSL services were provided through a dry loop, but once the Federal Communications Commission (FCC) made it mandatory for incumbent local exchange carriers share their lines with competing providers such as Verizon, the shared line became very common. This system allows for a single pair to transmit information with a DSLAM, and analog voice (phone conversion), at the same time.

Earlier ADSL standards were able to deliver 8 Mbit/s to the user over roughly 2km of ethernet cables (unshielded twisted pair copper wire). With the newest ADSL standard (ADSL2+), it is possible to deliver up to 24 Mbit/s, based on the distance from the DSLAM (usually located at the providers offices). Many customers are unfortunate, and further away from the provider than 2KM, which will result in reduced data transfer rates.



DSL Technology

The subscriber line PSTN (public switched telephone network) was initially designed to transmit analog voice transmissions (telephone conversions) and signaling. Although since the concept information transmission as we know of it today wasn't known. The phone systems regular frequency of transmitting voice transmissions is between 300, and 3,400 Hz, which is known as the range that human speech is required for it to be clearly intelligible. This is more commonly referred to as voiceband.

Once the analog voice transmissions reach the central office (telephone exchange), speech is digitized into a 64 kbit/s data stream in the form of an 8 bit signal, through using a sampling rate of 8,000 Hz. Through the Nyquist–Shannon sampling theorem, all signals above 4,000 Hz will not be passed by the phone network.

Through the laws of the Shannon–Hartley theorem (the Shannon limit), there are limits to the speed of data transmission. In the earlier days of telephony, it was thought that a standard phone line couldn't be pushed beyond the low speed limits of data transmission (generally under 9,500 bps). During the 1950s, 4 MHz television signals were commonly transmitted through standard twisted pair telephone wire; suggesting that the Shannon limit would allow for the transmission of many Megabits per second. Although, there was a fault with said suggestion, the current twisted pair telephone wire had many impairments, thus limiting these rates, and making them far to impractical. During the 1980s new techniques where developed for that limit to be greatly exceeded.

The local loop that connections the telephone switch to subscribers, is able to route frequencies far beyond the plain old telephone service limit of 3.4 kHz. Depending on the distance, and strength of the local loop limits can reach up to tens of megahertz. DSL uses this unused bandwidth of the loop by forming 4312.5 Hz wide channels, beginning at 10 and 100 kHz, based on how the system was configured. Channels are constantly checked for usability, in a similar way an analog modem would with a plain old telephone service connection. Very similar to an analog modem, a DSL transceiver will frequently monitor the durability and quality of each channel, then add or remove them from service based on their quality.

ADSL service supports two modes for transmission, interleaved channel, and fast channel. Fast channel is primarily for streaming video, and audio, were latency is everything. Interleaved channel is primarily for file transfers, where transfer errors are unacceptable.

The success of DSL largely reflects on how elections in recent decades have improved, and become less expensive. Laying fiber optic and copper cable still remains very costly. During the early 1990s the cost of Digital signal microprocessors for DSL technologies was far to expensive for DSL to reach the popularity that it has today. Advancements in VLSI technology in the late 1990s have reduced the cost, to the point where phone companies could profit off this technology. The DSL service could be deployed over an existing cable line, rather than the much more expensive task of installing new, fiber-optic cable. With the competition in Internet access, the costs of ADSL have dropped drastically, thus making ADSL much more economical compared to a dial-up service. These are the major factors in the popularization of DSL technology today.

Every type of DSL employs a very complex DSP (Digital signal processing) algorithm procedure to eliminate the inherent limits of existing twisted pair cabling. During the 1990s the price of such a signal processing system would be far to expensive. Thanks to the VLSI technology, the price of installing DSL on a standard existing local loop from DSLAM to DSL modem is far less than it would cost to install a brand new fiber-optic cable over the same distance.

Many residential, and small-office DSL services reserve low frequencies for voiceband services(telephone conversions). Splitters are able to split the DSL and voiceband frequencies from one an another allowing you to use existing voice service, and operate a DSL connection. Thus, allowing standard telephone services, fax machines, and analog modems to share the same wires as DSL. Only one DSL connection is aloud to use the subscriber line. The most common way to connect multiple computers to a DSL service is through a router or hub that will establish a connection from the DSL modem to a Ethernet, Wi-Fi or Powerline network on the customer's residence. The amount of landlines in the US has dropped from 189,000,000 in 2000, to 172,000,000 in 2005, while the amount of cellphone subscribers has grown. It is expected with VoIP becoming largely popular that this number will dramatically decrease again.



Setting-up a DSL Connection

Often DSL companies will offer a do-it-yourself service or installation at a fee. Many people are turned away by the do-it-yourself package due to the lack of technical knowledge. Although it's easier than most think, a standard DSL self installation kit consists of full instructions to guide you through the process. Included in the package is, the appropriate cabling, DSL modem and adapter along with a CD that installs the needed software on your PC. It is important to make sure your computer contains a network card. Some DSL packages will include this, although installation of it requires some technical knowhow.

Once installed the modems start up process generally consists of:

• Self test to ensure the modem is running correctly.
• Checking the connection between the computer and modem, this is generally done through the Ethernet or USB port.
  

• The modem attempts to connect with the Digital subscriber line access multiplexer (DSLAM). Information can only be passed into the computer when the modem and DSLAM are synchronized. The process is relatively quick (usually a few seconds) but is very complex. During this process most modems will have a light labeled "DSL" or "LINK", which will indicate if the modem is synchronized yet or not.  During the connection process the light flashes; when connected, the light stays lit.

Types of DSL

Distance from the telephone exchange DSLAM system is more restrictive for the higher data transmission types of DSL.



Edited by Administrator - 07 Jul 2008 at 8:57pm

Jason, for setting up one computer that's pretty much it. You may need to install a network card if your computer doesn't currently have one and possibly install software given to you by your provider. For multiple computers you'll need to purchase a hub or router. 

how to uprgrade my connection....

how to use wireless??
how to set up wireless?

is broadband the same as broadband?