Digital Subscriber Line (DSL) - Term Paper Example

 Digital Subscriber Line (DSL) Abstract Technology is changing at an alarming change in today’s dynamic world. Electronic devices, more so computers, are getting outdated before they even get paid off. This rapid change in technology is also the same with the internet where there is an ever-growing demand for high speed internet. Initially, traditional modems were used for internet connection but after reaching their peak data rate, a new technology had to be developed in order to provide internet access at a higher speed. This technology, known as Digital Subscriber Line (DSL), makes use of standard copper telephone lines to supply secure and high speed internet access. Transmission of high speed data is facilitated by a new technology known as Discrete Multitone (DMT). Its connection speed ranges between 128 Kbps upstream to 1.44Mbps and 512 Kbps downstream. The DSL technology is a family consisting of VDSL, ADSL, HDSL and RADSL. ADSL is the most used technology of the three due to its high data rates and ability to allow users talk on the phone and use the internet simultaneously (Maznets, Online). The DSL technology is the subject of this report. The report discusses its general history, applications and its future in detail as well as its other features. General History Despite being termed as a new technology, the history of DSL dates back to 1800 when the first telephone was invented by Alexander Graham Bell. This invention was the first stage in the evolution process of DSL technology. However, the main theory behind DSL came to life in 1980 when Joseph Lech discovered that data can be transmitted via broadband signals. In 1984, the ISDN (Integrated Services Digital Network) specification was approved and it was the main motivation behind DSL technology (Syix, Online). ISDN was later reused as IDSL (ISDN Digital Subscriber Line). In 1988, ADSL was developed and its patent signed. ADSL (Asymmetric DSL) was of major significance as it allowed users to download data at speeds faster than their speed of upload. ADSL then began its transition from analog to digital when the demand for increased speeds increased. The technology has already debuted in the market in the form of ISDN. ISDN refers to digital phone connections that have been networked to facilitate the transfer of both voice and data. Through ISDN, more data can be transmitted around the world at much higher speeds. In the transition process, Discrete Multitone was developed by John Cioffi. A DMT ADSL signal is contained into 256 frequency channels. Cioffi’s version of DSL technology was proven to be better than all its competitors hence became an industry standard (Fierce Telecom, Online). In the 1990s, High Bit-Rate DSL (HDSL) was developed and had the same bandwidth in upload and download. It was used more frequently for data transmission between consumers and phone companies. As the DSL technology progressed over the years, it was expanded into a number of technologies (Bagad, 8). These include; (a) ADSL – A higher bandwidth DSL for downloading and uploading (b) RADSL (Rate adaptive DSL) – the speed of transfer of signals can be adjusted using a software (c) VDSL (Very high data rate DSL) – has a very high transfer speed but works best over short distances. Relationship with OSI Model Just as all other types of computer communication systems, transfer of data in a DSL network is defined in the OSI model. The Open Systems Interconnection (OSI) model was first introduced by the ISO in the late 1970s. It shows how communication can be facilitated between various systems without the need of a change to the logic of the underlying software and hardware. According to Forouzan (29), the OSI is a model for identifying and designing flexible, interoperable and robust network architecture. The OSI model divides the various tasks involved in the process of transfer of information into 7 sub groups. Each sub group is known as a layer and is described briefly below. 1. Physical Layer It coordinates the functions necessary in order to transmit a stream of bits over a physical medium. The layer also defines the functions and procedures that have to be performed by physical interfaces and devices in order for transmission to take place (Forouzan 33). 2. Data Link Layer It takes data frames from the network layer and provides for their transmission. 3. Network Layer Addresses data frames and ensures that they are sent to the correct destination by translating logical addresses and names to physical addresses. 4. Transport Layer Ensures that data delivery is done in an error free manner without any loss, corruption or duplication. 5. Session Layer It allows 2 applications to establish, connect and disconnect a connection. 6. Presentation Layer This layer determines the type of format used in data exchange among networked computers. 7. Application Layer It provides applications that have access to various network services (Forouzan 41). DSL technology operates at the bottom two layers, the Physical and Data link layers, of the OS model. The other layers from layer three depend on the type of applications and network protocols that are to be run. Physical Layer As discussed earlier, this layer defines the operating specifications, electrical and physical properties for the media and devices used in connection. The main purpose of this layer is to facilitate the physical connection of the media and how it is configured. In DSL technology, this layer mostly deals with the bits of data and the medium involved in moving the bits. In this case, the medium/hardware used for transfer of information is the copper lines. In DSL, the physical layer controls transmission of data on the phone lines and facilitates the end to end connection between the user’s home and the internet/telephone company. According to Forouzan (33), the physical layer also defines functions and procedures that the connecting devices and interfaces have to perform in order for transmission to take place. The following figure illustrates the position of the physical layer with respect to the medium of transmission and the data link layer. In DSL, the physical layer is made up of a stream of bits, with no interpretation, in the form of 0s or 1s. For the data to be transmitted, the bits require to be encoded into signals. The type of encoding necessary is defined by the physical layer (Forouzan 33). It also defines how long a bit lasts, synchronizes the sender and receiver clock and defines the direction of transmission between the two communicating devices. The direction of transmission may either be simplex (one device sends while the other receives), half duplex (both devices can send and receive but not simultaneously) or Full Duplex where the devices can send and receive data at the same time (Goleniewski, 162). Data Link Layer It is the second layer in the OSI model and it transforms the raw transmission from the physical layer to a reliable link. Its main responsibility is error detection and correction. It provides for the transmission of data messages taken from the network layer. In a DSL connection, the Data Link layer receives incoming messages at the receiving end and sends it for handling at the network layer. This layer then uses the Physical layer to error-free data delivery between the two communicating ends (Forouzan 34). It achieves this by packaging information received from the network layer into a frame that contains error detection information. At the receiving end, the data link layer reads the incoming frame and then uses the received frames as a basis for generating its own error detection information. After the entire frame has been received, it compares the value of the incoming frames to its error detection value. If the two frames match, the layer approves that the frame received is correct. In a DSL, the data link layer also has other responsibilities apart from error correction. Other functions of the data link layer are; Other functions of the data link layer include framing (dividing the received bits into manageable units (frames)), physical addressing (adds a header to the frames allowing them to be easily distributed to different systems on the network), flow control (it imposes a mechanism for controlling the rate of data flow to prevent the receiver from being overwhelmed) and access control (Through its protocols, it makes it possible to determine the device that has control over the communication link) (Forouzan 35). Application layer This layer facilitates access of the network by the user, whether human or software. It achieves this by providing a user interface and support for certain services such as email. This layer allows users to access, read and/or edit data from a remote host, manage files in a remote computer as well as to retrieve files from the remote computer and use them in the local computer. Generally, the main responsibility of this layer is to allow access to resources in a network through the use of programs (Archaya 196). Despite each application being different, some are very vital to an extent that they have become standardized. The following standards have been defined in the internet; (a) File transfer Protocol (FTP) Mainly deals with authentication. It is used in connecting to a remote machine and fetching or retrieving data. (b) Remote login Also known as telnet, this is a remote terminal protocol that enables a user on one site to establish a TCP connection to a different site (Archaya 196). Other standards include Mail (SMTP), News (NNTP) and Web (HTTP) (Hardy 432). Areas of Application of DSL Technology The DSL industry is expanding rapidly and the technology is clearing billions in total service revenue (Golden 14). This technology has had a profound effect on the communications industry. As a result of its success, the technology has been applied in various areas, to provide its users with its high speed voice and data connection. The following section discusses some of the main areas where this technology is applied. The most common area of application of this technology is residential homes and businesses. Using 2 copper telephone wires, telephone and internet companies can easily supply home and business users with high speed voice and internet services. DSL becomes appropriate for use in these places as it allows for users to access the internet and talk on the phone at the same time. This technology is also used in residential houses where the residents are supplied with television channels where they can watch unlimited movies from their homes. DSL has led to the development of Video on Demand, which provides the cable TV services that allow subscribers to access over 500 TV channels (Golden 14). Another major area of application of DSL technology is in telephony. Using the copper cables, DSL allows for exchange of information between people either near or far via the telephone. The copper lines can run for long distances hence providing telephone services to areas that were otherwise unreachable. The Future of DSL Technology Since its establishment in the early 1980s, DSL technology has evolved over time and has had a fundamental impact on the communications industry. The future of this technology looks very promising as it is still evolving and getting better by the day. More applications for high speed DSL are been developed, as the developers seek to satisfy the ever-increasing demand of high speed internet. Consumers around the world are in need of affordable high speed voice and internet connection for various purposes such as online learning, online gaming, music and movie downloads and internet shopping. With this ever increasing demand in the market, DSL will seek to meet these demands as it can easily supply the required services. In conclusion, it is safe to say that the future of DSL is promising, and this technology is here to stay. Works Cited Archaya, Vivek. TCP/IP Distributed System. New Delhi: Laxmi Publications. 2006 Print. Bagad, V.S. Telecommunications Switching Systems and Networks. New Jersey: Technical Publications. 2009 Print. Fierce Telecom. John Cioffi, The father of DSL Technology.4 October 2011. Web 29 November 2012 Forouzan, Behrouz. Data Communications and Networking. New York: McGraw Hill. 2007 Print. Goleniewski, Lilian. Telecommunication Essentials: The Complete Global Reference Source to Communications Fundamentals, Data Networking and the Internet, and Next-Generation Networks. Boston: Addison-Wesley Professional. 2006 Print. Golden, Philip. Implementations and Applications of DSL Technology. Florida: CRC Press INC. 2008 Print. Hardy, Daniel. Networks: Internet, Telephony, Multimedia. New York: McMillan Publishing. 2002 Print. Syix. History of DSL. 14 march 2001. Web. 29 November 2012. Maznets. ADSL Technology. n.d. Web 29 November 2012. Read More