Dsl technology report

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Dsl technology report

  1. 1. BANSAL INSTITUTE OF ENGINEERING & TECHNOLOGY, LUCKNOW Seminar REPORT ON DIGITAL SUBSCRIBER LINE SUBMITTED TO: MR.PAWAN KUMAR SAINI H.O.D. (EC) SUBMITTED BY: ANANT PRATAP SINGH rd EC- 3 yr. ROLL NO. 1042231009
  2. 2. DSL TECHNOLOGY ACKNOWLEDGEMENT It is pleasure for me to present this seminar regarding the “DIGITAL SUBSCRIBER LINE (DSL)” Today, high-speed Internet access has become quite a necessity, not only in the advanced nations but also in many of the third world countries. I would like to thank everyone who helped to see this seminar to completion. In particular, I would like to thank my seminar incharge Mr. Ankur Shukla for their moral support and guidance to comlete my seminar on time. I am sincerely thankful to Mr. Pawan Kr. Saini(HOD EC.) for giving me suggestion to complete my seminar in a right way and at the time. I express my gratitude to all my friends and classmates for their support and help in the seminar. ANANT PRATAP SINGH E.C 3 YR. RD 2
  3. 3. DSL TECHNOLOGY S.NO. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. NAME OF TOPICS HISTORY OF DSL WHAT IS DSL? BASIC TECHNOLOGY(OPERATION) COMPARATIVE STUDY OF DSL FLAVORS WHAT IS CABLE INTERNET CONNECTION? TYPES OF DSL ADSL(Asymmetric Digtal Subscriber line) VDSL(Very high-bit rate Digital Subscriber line) RADSL(Rate-Adaptive Digital Subscriber line) HDSL(High bit/data rate Digital subscriber line) ISDN DSL(Integrated Service Digital Network) DSL DEVICE DSL VS CABLE APPLICATION ADVANTAGES DISADVANTAGE SUMMARY OF DSL CONCLUSION REFERENCE PAGENO. 4 5 6 7 7 8-9 8 8 8 8 8 8 10-11 11 12 13 14 15 16 LISTS OF FIGURES S.NO 1. 2. 3. 4. 5. 6. FIGURE NAME BASIC DSL NETWORK BASIC TECHNOLOGY(OPERATION) COMPARATIVE STUDY OF DSL FLAVORS BASIC CABLE NETWORK WORKING OF A SIMPLIFIED ADSL GENERAL MODEM FOR DSL DEVICE 3 PAGE NO. 5 6 7 7 8 10
  4. 4. DSL TECHNOLOGY HISTORY OF DSL MODEM (Modulator-Demodulator) used for communication between any two computers through a PSTN line uses Modulation and Demodulation techniques for Digital-Analog and Analog-Digital conversion, respectively. In 1969, AT&T revised the tariffs to allow customer-provided devices (modems) to beConnected to PSTN lines for transferring data, with the following conditions: Restriction inoutput power and energy levels Connection to the PSTN (Public Switched Telephone Network) thru the telephone companyprovided protective devices (Data Access Arrangement). All the network-control signaling ( Dialling , Busy signals, etc.) performed with the Telephone company -provided equipment at the connection point.Under these conditions, modem technology had to come up with the following new Techniques in order to achieve higher data rates (from 19.2 Kbps thru 56 Kbps): Error Correction Ec Cancellation ho Modem data rates are calculated using Claude Shannon‟s formula: C = B * log2 (1+ S/N) where ,C = Channel Capacity (2400 to 2800 Hz) B = Bandwidth (24000 bps) S/N = Signal-to-Noise Ratio (24 to 30 dBs) The limitations in achieving higher data rates thru these voice band lines are mainly due to the core network and not the bandwidth availability of the copper wire of the telephone network. Filters at the core of the network limit the voice-grade bandwidth to approximately 3.3 KHz. In the absence of these filters, the copper wires can up to a few frequenciesMHz.It is precisely this aspect that is made use of in the DSL technology, which came into existence in the late 1980s. 4
  5. 5. DSL TECHNOLOGY WHAT IS DSL? Digital Subscriber Line (DSL) is a technology that provides digital data transmission over the existing wires of local telephone network. DSL service is delivered simultaneously with regular telephone on the same telephone line. This is possible because DSL uses a higher frequency. These frequency bands are subsequently separated by filtering. Fig1: Basic DSL network Digital Subscriber Line (DSL) is a broadband high-speed Internet technology that brings highbandwidth information to home and offices over ordinary copper telephone lines. It assumes that digital data does not require changing into analog form and back to digital form. Digital data is transmitted directly to the computer, as is, exploiting the maximum bandwidth and the wide range of unused frequencies available in the existing copper wire of telephone networks for high-speed broadband communication. Moreover, the signal can also be separated, if one chooses, so that some of the bandwidth is used to transmit an analog signal for simultaneously using the telephone line for voice. Following are some of the key features of DSL: Distance sensitive technology. Internet connection is always ON . Simultaneous use of the phone line for voice as well as data traffic. Internet Connection is highly reliable and secure . High Speed (Mbps) vis-à-vis a regular modem (56 Kbps max). 5
  6. 6. DSL TECHNOLOGY Basic technology(Operation) Telephones are connected to the telephone exchange via a local loop, which is a physical pair of wires. Prior to the digital age, the use of the local loop for anything other than the transmission of speech, encompassing an audio frequency range of 300 to 3400 Hertz (voiceband or commercial bandwidth) was not considered. However, as long distance trunks were gradually converted from analog to digital operation, the idea of being able to pass data through the local loop (by utilizing frequencies above the voice band) took hold, ultimately leading to DSL. The local loop connecting the telephone exchange to most subscribers has the capability of carrying frequencies well beyond the 3.4 kHz upper limit of POTS. Depending on the length and quality of the loop, the upper limit can be tens of megahertz. DSL takes advantage of this unused bandwidth of the local loop by creating 4312.5 Hz wide channels starting between 10 and 100 kHz, depending on how the system is configured. Allocation of channels continues at higher and higher frequencies (up to 1.1 MHz for ADSL) until new channels are deemed unusable. Because DSL operates above the 3.4 kHz voice limit, it cannot pass through a load coil. Load coils are, in essence, filters that block out any non-voice frequency. They are commonly set at regular intervals in lines placed only for POTS service. A DSL signal cannot pass through a properly installed and working load coil, while voice service cannot be maintained past a certain distance without such coils. Therefore, some areas that are within range for DSL service are disqualified from eligibility because of load coil placement. Fig2: Basic Technology(Operation) 6
  7. 7. DSL TECHNOLOGY Comparative Study of DSL Flavors XDSL Series ADSL ADSL2 ADSL2+ RADSL VDSL HDSL IDSL Type Asymmetric Asymmetric Asymmetric Asymmetric Asymmetric/Symmetric Symmetric Symmetric Down Speed 6-8Mbps 12 Mbps 27 Mbps 640-2200Kbps 13-52 Mbps 2.3 Mbps 144 Kbps Up Speed 640Kbps 1Mbps 1Mbps 27-1088Kbps 1.5-2.3Mbps 2.3Mbps 144Kbps Distance 12000-18000ft. 6000ft. 3000ft. 18000ft. 4500ft. 12000ft. Morethan 2000ft. Fig3: Comparative study of different DSL flavors What Is a Cable Internet Connection? Cable internet connection is an internet connection designed to operate over existing cable TV lines. Cable Internet access requires a Cable Modem (CM) at the customer's premises and a Cable Modem Termination System (CMTS) at a cable operator facility. The two are connected via coaxial cable because the coaxial cable used by cable TV provides much greater bandwidth than telephone lines. Cable Internet systems can typically operate where the distance between the modem and the termination system is up to 100 miles (160 km). Fig4:Basic Cable network 7
  8. 8. DSL TECHNOLOGY TYPES OF DSL  ADSL(Asymmetric Digital Subscriber Line)  VDSL(Very high-bit-rate Digital Subscriber Line)  SDSL(Symmetric Digital Subscriber Line )  RADSL(Rate Adaptive Digital Subscriber Line)  HDSL(High bit/data rate Digital Subscriber Line)  ISDN DSL(Integrated Service Digital Network) Asymmetric Digital Subscriber Line (ADSL): Most home and small business users typically use ADSL. The transfer of data from the internet to PC is much faster than the transfer from PC to internet. Downstream speeds for ADSL range from 1.59 Mbps, while upstream speeds are up to 1.5 Mbps, for a distance of 18,000 feet from the service providers premises. Fig5: Working of a simplified ADSL 8
  9. 9. DSL TECHNOLOGY Very high-bit-rate Digital Subscriber Line(VDSL): Provides high speed internet connection but works only over a short distance. Symmetric Digital Subscriber Line (SDSL): Does not allows to use the phone at the same time. But internet speed of sending and receiving data is same. Rate Adaptive Digital Subscriber Line (RADSL): This service is a variation of ADSL but the modem can adjust the internet speed . High bit/data rate Digital Subscriber Line(HDSL): HDSL was the first DSL technology that used a higher frequency spectrum of copper, twisted pair cables. Integrated service digital network(ISDN DSL): Symmetric data rates of up to 144 kbps using existing phone lines. Capable of using the same modem or terminal adaptor used for ISDN and is always available. 9
  10. 10. DSL TECHNOLOGY DSL DEVICES DSL is actually not a physical line, but a modem pair. One DSL modem is located at the customer premises (Customer Premise Equipment or CPE) and another DSL Access Multiplexer (DSLAM) is at the Central Office (CO). These two modems create a Digital Subscriber Line or DSL. DSL modems transmit data at the rate of up to 160 Kbps over copper lines, up to 18000 feet.DSL Modem or DSL Transceiver, as it is also referred to as, is connected to the customer‟s computer via USB or a 10-Base T connection. DSLAM at the Central Office or the Access Provider is the one that actually makes the DSL happen . It accepts connections from various customers and aggregates them into a single high capacity connection to the Internet. In addition, the DSLAM also does IP routing and Dynamic IP address assignment. Fig6: GENERAL MODEM FOR DSL DEVICE 10
  11. 11. DSL TECHNOLOGY DSL V/S CABLE Both DSL and Cable Modem technologies offer high-speed Internet access. Even though they are similar in many respects, the two technologies differ on some fundamental aspects such as speed, availability , bandwidth, security, reliability and quality of service. Availability: DSL was first designed in the 1970„s whereas Cable„s HFC was designed in the 80s and 90s. Roughly 80 to 85 percent of America's 68 million cable TV subscribers (say, 55 million or so) can get high-speed access, says Instat-MDR analyst Mike Paxton. DSL access is a little spottier, though Instat‟s Ernie Bergstrom puts the number above 50 million. In terms of worldwide broadband market share, currently DSL has higher market share compared to Cable but in coming years picture may change. Speeds: The topic of "which is better and faster" has been a highly debated topic, and still there doesn't appear to be a clear winner. DSL offers users a choice of speeds ranging from 144 Kbps to 1.5Mbps. Cable modem download speeds are typically up to 2 times faster than 1.5Mbps DSL, but the reason there is no clear speed winner is because cable technology is based on shared bandwidth, with many factors influencing a user„s download speed. With shared bandwidth the speed fluctuates depending on the number of subscribers on the network. With DSL, the connection is kind of dedicated and not shared, and user gets more or less an invariable speed. This is one reason why cable broadband providers don't often publish speed information. In more rural areas with fewer subscribers, users bound to have faster download speeds than a user in a metropolitan center. Because cable modem speeds fluctuate, it is difficult to gauge an exact download speed. On the upload stream, however, cable and DSL are closely matched for speed. Both DSL and cable Internet speeds are largely dependent on the service provider and either the distance away from the switching station a user is or how many users are in an immediate area. Bandwidth: 11
  12. 12. DSL TECHNOLOGY Cable modem technology delivers “shared” bandwidth within the neighbourhood, while DSL delivers“dedicated” bandwidth. DSL typically is provided in the range from 128 kbps to 1.544 Mbps, varying as the equipment. Security: DSL can be considered to be more secure of the two, more due to a perceived weakness in the cable modem. All cable modem customers in a region belong to the same LAN, thus opening avenues for file sharing and other menaces of a typical network neighbourhood. This calls for security firewalls, strict authentication and packet filtering mechanisms to be built into cable modem standard specifications. Reliability: Both DSL and Cable provide an “always on connection” capability, thereby giving a “Static IP address” to the session; and in turn, providing a fixed target to network attackers. As a result, many DSL and cable customers have to purchase a DSL Router or a Cable Router, that enhances the functionality of a basic modem with security features such as packet filtering and network address translation. Customers can choose from a variety of precautions offered by the broadband router, to suit their applications. Despite tall claims by vendors about out-weighing the benefits of one another, both DSL and Cable modem providers are working towards winning customers and expanding their customer base. Drastically cutting costs, providing more value-added services, improvising on the security features and constantly withstanding competitive pressures from vendors of the other forms of technology, both forms of broadband technology are here to stay for some more time. 12
  13. 13. DSL TECHNOLOGY APPLICATIONS Interactive Video – movies on demand , video on demand , video conferencing. High-speed Data communication – Internet access , Telecommuting , Remote LAN access ,specialized network access. ADVANTAGES DSL service is always ON and we can still use the phone for voice calls. Broadband speed is much faster than dial up service. Fixed monthly billing, regardless of time usage. Digital data is directly transmitted to computer as digital data which uses much wider bandwidth for transmitting. DISADVANTAGES DSL has one significant downside: As you move away from the central office , the connection becomes slower. This results is distortion of signal. 13
  14. 14. DSL TECHNOLOGY Summary Of DSL The growth in demand for access to the Internet by business and residential end users has been increasing for a number of years. The content available on the Internet and the applications required to access it have also developed to meet end user demand and become ever more complex and sophisticated and have, in turn, driven demand for greater delivered bandwidths to maximize operational performance. Forecasts for growth in bandwidth requirements are based upon a number of factors, future demand for services such as “Triple Play” using standard and high definition IP Television is often cited as a driver for the provision of ever increasing bandwidths although there is considerable debate over the dynamics of this market. This paper assumes that the demand for higher bandwidths will continue to increase, and examines the capabilities and limitations and the current and future roles that Digital Subscriber Loop (DSL) technologies have in delivering ever higher bandwidths to end users to meet demand for access to developing services. 14
  15. 15. DSL TECHNOLOGY Conclusion The development of Digital Subscriber Loop technologies has enabled the delivery of high bandwidth broadband services to end users connected to the copper access network. However, the intrinsic limitations of the copper cables impose a finite limit on the maximum bandwidth that can be delivered to end users. Given that forecasts for bandwidth demand indicate a continuous increase, DSL technologies seem to offer - at best - an interim solution to the problem of providing genuinely fast broadband services. Although end user demand for standard and high density IP Television is often hailed as a major driver for the provision of high-bandwidth networks, the continuing slow take-up of IPTV offerings in the UK would seem to make it unlikely that this sector will be sufficient to drive a significant increase in bandwidth in the UK. Instead, it is the ever-greater requirements for bandwidth to access more sophisticated content and to efficiently run the applications needed to exploit them which is likely to make the ubiquitous provision of high-bandwidth services a necessity, for both business and domestic users across a range of urban, rural and suburban environments. As requirements for universal Internet access combined with greater bandwidth increase, and the associated problems with providing high bandwidths over legacy copper access networks threaten to expand the phenomenon of the digital divide to include not just remote rural areas but populous suburbs as well, so increased attention will need to be devoted to the underlying issues of broadband access. As already discussed, one obvious solution lies in the construction of Next Generation Access networks using both hybrid copper/fibre networks and all-fibre networks to deliver bandwidths of 50 Mbps and above to large numbers of end users. Negative aspects, however, include the substantial levels of investment by network operators or public/private partnerships required to make this a reality, and the degree of disruption inherent in laying new infrastructure by trenching in existing built environments. Solutions to the latter exist in the possibility of running fibre circuits through sewers, or in carrying them on overhead rights-of-way, but both suffer from drawbacks in terms of the vulnerability to damage of the circuits and the potential difficulty 15
  16. 16. DSL TECHNOLOGY REFERENCES International Telecommunication Union (ITU). G.992.1 (G.dmt), G.992.2 (G.lite) standards information. http://www.itu.int American National Standards Institute (ANSI). ANSI TI.413 -1998, ADSL Metallic Interface. http://www.ansi.org Universal ADSL Working Group. G.lite standards information. http://uawg.org Standards Committee T1 -Telecommunications. XDSL standards and relevant documents from T1E1.4 Working group. http://www.t1.org Europ Telecommunications Standards Institute (ETSI). ADSL, VDSL and SDSL ean standards. http://www.etsi.org Internet Engineering Task Force (IETF). ADSL MIB working group. http://www.ietf.org, http://www.ietf.org/html-charters/adslmib-charter.html 16

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