Digital Subscriber Line technologies

Essay by m5wongUniversity, Bachelor'sA+, October 2004

download word file, 13 pages 3.0


In today's fast paced society, people are constantly searching for new ways to improve their speed of data transmission. DSL (Digital Subscriber Line) is an answer to the needs of our society. DSL is a means of providing users with high data transmission speeds with high levels of bandwidths all over the medium of the simple copper telephone wire. DSL and the development of various types of DSL has become an essential part of our information based economy. DSL comes with numerous advantages and disadvantages, therefore, before a business can make an informed decision on whether or not to implement a DSL solution, they must first evaluate all the various aspects of DSL technologies. The purpose of this paper is to outline some of the basic factors of DSL and explain its functionality and purpose in our information driven society.

What is DSL?

DSL (Digital Subscriber Line) is a new type of services that provides home and business users a fast internet connection as compared to modem dial up.

DSL uses the medium of the twisted copper pair wires from the telephone to receive and transmit data without having to tie up the household telephone line. This service allows for various high bandwidth applications such as audio and video streaming, online games, tele-conferencing etc. There are many different types of Digital Subscriber Lines, more generally they are known as ADSL and XDSL. The difference between the types of DSL are their different speeds of transmissions for downloading and uploading. The different technologies available other than ADSL are R-ADSL, ADSL Lite (also known as the new G-Lite Technology), HDSL, SDSL, and VDSL.

xDSL refers to all the different types of DSL currently available. The "x" denoting any of the letters that would come before the DSL. The term xDSL is the generally accepted abbreviation for all the various types of DSL on the market.

xDSL technology is enabling a consumer to utilise their existing telephone connection to have high speed internet access. It splits the connection into two, whereby any frequency less than 4kHz is reserved for voice and faxing, and anything greater than that is used for data transmission purposes.

How DSL Works

DSL works by utilising an existing POTS telephone line's unused capacity. This is because the twisted pair copper wire used for the local loop has a bandwidth of up to 1 megahertz, but the analog voice channel uses only the 0 to 4,000 hertz range (Peden, 2001, p.266). What DSL does is utilize the unused bandwidth that is not needed by normal voice conversations as digital channels, unlike traditional internet access via modems which have to convert digital data into analog for transmission through the phone line. (Yen, 2001, p.29) This allows DSL to be concurrently used with normal voice transmissions since DSL transmissions are occupying the upper frequencies. To prevent the DSL signals from interfering with regular voice transmissions, devices which block out the higher than 4Khz frequencies called low pass filters are installed on the phone lines that are not connected to the DSL modem (Franklin, 2003). DSL divides the bandwidth unused by analog voice transmissions into 2 channels, one for sending and the other for receiving (Yen, 2001, 30). How much bandwidth is allocated for sending/receiving is dependant on the version of DSL which the provider has chosen to implement.

However, these speeds for DSL vary based on distance from the end user to the CO. As the distance increases, the speeds fall. "The limit for ADSL service is 18,000 feet (5,460 meters), though for speed and quality of service reasons many ADSL providers place a lower limit on the distances for the service. At the extremes of the distance limits, ADSL customers may see speeds far below the promised maximums, while customers nearer the central office have faster connections and may see extremely high speeds in the future" (Franklin, 2003). At the central office of the DSL service provider, there is a piece of equipment called a DSLAM (DSL Access Multiplexer) which communicates with each of the end users' DSL modem. The DSLAM is what connects all of the end users in a particular geographic area around the CO to the internet through a single high speed connection (Franklin, 2003). The follow diagram illustrates this as well as how the rest of the connections are made at the end user side.

Applications of DSL Technology

There are a number of applications of DSL for home and business users which include, but are not limited to the following: E-commerce/On-line shopping, LAN Access from home, multimedia applications, hosting of web servers and distance learning.

E-commerce/On-line Shopping: DSL will speed up the process in which electronic transactions are done by limiting the time needed for pages to download.

Remote LAN: "With DSL, employees can access their corporate LAN from home and maintain productivity with faster response times than a dial-up connection." (Verizon, 2003). Essentially, activities, information, and resources can be acquired from the office in a fraction of the time it takes for other connection types.

Multimedia Applications: DSL's large bandwidth provides users quick download speeds of videos, music, games, and entertainment.

Hosting of Web Servers: Users can host web servers and have one less variable to worry about - available bandwidth. With DSL's available bandwidth, load speeds are always quick and this can be especially beneficial for web sites which have a large amount of multimedia content.

Distance Learning: Allows employees of a company and students of a school to take part in learning even though they may be separated physically. An example of this is telemedicine - wherein students learn certain medical procedures by viewing a live operation over the internet (Kuszler, 1999).

Data Transmissions: Sending and receiving data can be done much more proficiently by using a DSL connection due to the large bandwidth.


In North America, high-speed internet surfing and downloading is a standard in most homes and businesses it is becoming more of a necessity than a luxury. The two most common broadband uses are with either cable connections via the "already in place television coaxial cable" (Chartrand) or with DSL by using existing twisted copper phone lines. Although North America has a steadily growing population of DSL subscribers, the rest of the world is absolutely booming with new subscriptions. All across the globe users have chosen DSL technology to satisfy their business, entertainment, and social needs, thus making DSL "the world's most popular broadband technology" (The following chart shows a regional breakdown of DSL subscriptions around the world.

A Canadian perspective will be used in comparing DSL with competing technologies. The number of available DSL providers in Canada has grown in the past number of years. Currently there are over 30 ISPs that offer DSL in Canada (, 2003). These include companies such as: BestWeb Internet, Silicon Networks, and namely In terms of cable modem connections, Roger's is the most common provider as cable internet is usually provided by the local area cable provider.

Before a business decides which technology to use, they must first do a self analysis of how many computers they require to be connected via the DSL or cable line, what minimum transmissions speeds are required, and how much is the company willing to spend on a monthly/annual basis to deploy these services.

Using a DSL line versus cable connections can have its advantages and disadvantages. Bell Sympatico currently uses twisted copper wiring, therefore connection speeds vary based on the distance from the CO and size of the copper wiring. Roger's High Speed can also be a viable choice, but given that it uses the coaxial cable to provide a connection, it may be split a number of times thus reducing connection speeds, especially during peak times. Therefore in one location in a city, DSL may be a better choice than cable connections whereas in another part of the city, cable connections may have a faster connection speed than DSL based on the criteria mentioned earlier.

If more than one computer is to be hooked up in the business, Bell can have up to 6 computers connected to the network when using the Ultra High Speed connection, only charging a moderate $89.95. Roger's high speed also offers the ability for multiple computers to use their services in a company at the same time. It cost $10.00/mo to rent a maximum of 5 additional IP addresses (one IP address is required per computer station).

Future of DSL

DSL technology has been around for over a decade. The most popular type of DSL technology that brings high-speed Internet to residential areas is ADSL. ADSL has been available for five years and it has more than 35 million lines deployed worldwide. The most recent ADSL2+ technology can provide downstream rates of about 16 Mbps given that the user is no more than 3000 feet away from the connected CO. (Starr,2003,p29) The future of DSL lies on its ability to go faster and faster to feed the speed thirsty customers as their demands grow in an information-based economy.

Recently an even more powerful VDSL technology which offers even faster speeds than ADSL2+ is grabbing the attention of many DSL providers. It offers downstream data rates of up to 52 Mbps. That's more than three times what ADSL2+ can offer. (Tyson, 2003, p3) The only downside of VDSL is that it can only be offered through a short distance of copper wires.

VDSL technology has been in development for several years. It wasn't considered a plausible technology for mass commercialization, mainly due to its relatively short reach. But in recent years many phone companies are implementing FTTC (fibre to the curb) or FTTN (fibre to the neighbourhood) to increase bandwidth and reliability. (Starr,2003,p29) This also provides a great solution to VDSL's short reach. With fibre optic cables reaching right up to a junction box near your neighbourhood, the only copper in the network is the line running from the box to your home. That line is most like short enough to provide VDSL service. All you would need is a VDSL transceiver in your home and a VDSL gateway in the junction box the distance problem could be overcome. The gateway would convert all the signals from the VDSL transceiver to pulses of light to be carried through the fibre optic cable to the CO.

Of course this technology is still in its early stages of development, because most neighbourhoods are not covered by fibre wire yet. But with the coverage of fibre optics increasing you can be sure that VDSL will become a cheap and comprehensive business solution.

Another up and coming DSL technology is VoDSL (voice over DSL). VoDSL offers to provide multiple phone lines and internet over the existing copper wires through DSL technology. The total number of voice lines that could be offered depends on the compression and line speed.

VoDSL has a great future commercially as it provides a good comprehensive solution for small to medium companies by offering multiple voice lines and high speed data transfer all using available proven DSL technology. In crowded markets, where precious copper loops are in high demand the application of VoDSL technology could prove to be very profitable to the carriers. In fact a number of researches have shown that the anticipated services revenue for VoDSL is expected to be near the neighbourhood of US$13billion. (IEC, 2003, p5)

The DSL technology has endless limitations. It will continue to evolve and improve to meet the high demands of today's highly competitive telecommunications market. DSL's potential to reach mass populations around the world and its ability to compete with other high-bandwidth data transfer technologies means that DSL will have a bright and successful future.

Interview with a Sympatico Employee

To help further our understanding of DSL and DSL service in our region of Canada, as a group, we were able to contact a former Customer Service Representative for Bell Sympatico High Speed Service. Zack Riviera was an employed at Sympatico in 2002-2003 at their outbound calling centre. As a telephone representative, Mr. Riviera was at the frontlines Sympatico's operations with their customers. As a group, we felt that he would have some relevant insight as to not only how the company and products work and are sold, but information on the service and customer satisfaction as well.

Our group compiled a number of questions regarding Sympatico's internet and customer service. Attached below are the answers that Mr. Riviera was able to provide for us.

What types of DSL does Sympatico currently offer?

The current service that I was selling at our particular call centre was ADSL (Asymmetrical Digital Subscriber Line). In our call centre we dealt mainly with only personal home users, not businesses. This is because ADSL offers faster downloading time, and slower uploading capabilities, which, according to a lot of my interaction with the consumers, is what they are looking for in an ISP.

What are the major DSL competitors in our region of Ontario?

Bell Sympatico is the only DSL provider in our immediate area. Therefore, there aren't any other companies that they are competing with in regards to DSL specifically. The major competitors for Bell Sympatico would be more along the lines of other ISP companies. Companies such as Rogers Cable Internet or other dial up internet connections offer the most competition. However, due to the fact that dial-up is perceived to be a technology of the past by many users, Rogers is the main competitor with Bell.

Do competitors offer anything that Sympatico doesn't?

Well, Sympatico is simply a connection to the Internet. Therefore, all other ISP companies will offer the same service. The difference between the companies is just the speed and the price. Rogers does however, offer bundle packages to their consumers, which is something that Bell has yet to really take advantage of. Rogers offers bundles which include a cell phone and service, basic television cable and cable internet connection all for one set fixed price. Many consumers will call Sympatico and ask if we offer any bundles similar to Rogers, which we don't. It's an issue of convenience as well, because all of those things included in your bundle will all come charged on one bill as well. This convenience factor is something that consumers really appreciate.

What are the costs of having Sympatico in your home?

Sympatico offers three levels of service for different prices; the consumer chooses which level they want to buy depending on their personal needs. The three types of service that they offer are Sympatico Basic, Sympatico Regular and Sympatico Ultra. The Basic option costs approximately $25.00 and allows a maximum total of 10K per second. This is comparable to Rogers Light cable service which is approximately the same price and speed. Sympatico Regular retails for $44.95 a month and can reach optimal speeds of 1MB a second. The Ultra option costs $69.95 a month and can reach optimal speeds of 10K per second. But keep in mind; these are optimal speeds, which are not guaranteed for all hours of the day and at all times. DSL service speeds are often affected depending on the distance that you live away from the CO.

What are the major complaints that you have received from customers regarding your service?

The biggest complaint that I was receiving from consumers was regarding the downloading cap that Bell had implemented a few years back. The Basic option was capped at a 1 gig total for both uploading and downloading. The Regular service option was capped at 5 gigs, and the Ultra service was capped at 10 gigs per month. And as if this wasn't bad enough, many consumers were very angry at the way Bell handled their downloading implementation. Bell claimed to have informed all of their customers of this new cap via their Sympatico email accounts. However, many consumers claimed to have either not received that email, or say that they never check that account anyway, therefore they were not properly informed of this new cap. Many customers were also angry because the penalty that Bell enforced was to fine the customers $30.00 for going over their cap amounts. Needless to say, this infuriated many consumers which wanted to switch their service instantly and Bell has had a hard time trying to win back the customers that they lost to Rogers through the implementation of the downloading cap. As of last that I heard, Bell has removed the downloading cap from their service.

How often, or does Sympatico service ever go down?

Due to the fact that DSL is run over the telephone lines, having any service down time is extremely rare. Even through power outages the phone lines continue to work. Through the time that I was working for Sympatico, I did not encounter any customers who had any complaints about service being down. In fact, that was one of Sympatico's selling pitches, we often tried to sell the product to the consumer on the angle that telephone wires are more stable; therefore, they will receive significantly less down time as compared to cable internet providers.

Seeing as DSL is not available in all regions, what does Sympatico do if they receive a request for service from a consumer who lives out of area?

If having DSL is not possible, Sympatico also offers dial-up connections. Dial-connections come in three different plans: $10.00 for 10 hours a month, $19.95 for 100 hours a month, or $22.95 for unlimited hours of the internet every month.

Now that you are no longer an employee of Sympatico, and you are looking at the competing internet providers as a consumer, would you recommend Sympatico DSL service over cable service?

In all honesty, no, I don't believe that I would recommend DSL over cable. In my honest opinion, I don't feel that DSL is any better than cable and I don't feel that you are getting any particularly good deal when purchasing from Bell. I think it just depends on your needs. If you happen to live close to a CO, your DSL connection will be faster, therefore, it may be more worthwhile to purchase that. If you live in a neighbourhood that has many cable internet consumers, therefore bogging down your connection speed, then DSL may be right for you. My personal choice would be swayed by convenience, and I feel that Rogers is currently offering a more convenient product with their bundles. Convenience is a card that Rogers is really playing well, and Bell has yet to catch on to it.


In today's information age, people are presented with numerous choices when deciding upon which data transmission solution they wish to implement, whether in a business or personal setting. DSL has proven to be a forerunner in the quest for a faster connection, however, the choice to implement said technology, should not be made without proper consideration of both its limitations as well as its advantages. As shown in our paper, DSL has been able to adapt to the ever changing telecommunications environment. In order to stay competitive, DSL and its technologies will continue to evolve to meet the growing needs of people and businesses.