Published on November 26, 2007
ADSL (asymmetric digital subscriber line): ADSL (asymmetric digital subscriber line) Provided by: I- Ming, Chen (501005) Advisor: Professor Ausif Mahmood Spring 2003 ADSL (asymmetric Digital Subscriber Line): ADSL (asymmetric Digital Subscriber Line) Digital - means a line able to carry data traffic in its original form, as opposed to analogue Subscriber Line* - the line connecting the individual subscriber (eg a household) to the local exchange Analogue - phone lines used for voice phone calls until today have been analogue lines and we have used MoDems (Modulator-Demodulator) to convert the digital output of the computer to analogue form for transmission and back into digital form ADSL (asymmetric digital subscriber line) : ADSL (asymmetric digital subscriber line) unused frequencies on copper telephone lines to transmit traffic typically at multi-megabit speeds allow voice and high-speed data to be sent simultaneously over the same line. service is 'always available' With ADSL you are wired for speed. Advantages: Advantages Usually provide the modem as part of the installation Internet Doesn’t need new wiring Connection open and still use the phone line for voice calls Regular modem(1.5 Mbps vs. 56 Kbps) Disadvantages: Disadvantages Better connection if closer to the provider’s Faster receiving than sending data Not available everywhere ADSL is high-speed connection that uses the same wires as a regular telephone line: ADSL is high-speed connection that uses the same wires as a regular telephone line ADSL Equipment : ADSL Equipment ADSL uses two pieces of equipment, one on the customer end and one at the Internet service provider, telephone company or other provider of ADSL services. At the customer's location there is an ADSL transceiver, which may also provide other services. ADSL service provider has an ADSL Access Multiplexer (DSLAM) to receive customer connections. How ADSL Work : How ADSL Work POTS (Plain old telephone service) - refers to standard telephone service. telephone services based on high-speed, digital communications lines, such as ISDN and FDDI, are not POTS. main distinctions between POTS and non-POTS services are speed and bandwidth. POTS is generally restricted to about 52 Kbps (52,000 bits per second). POTS network is also called the public switched telephone network (PSTN). The Simple ADSL Transceiver: The Simple ADSL Transceiver ADSL frees the end-user from the limitations of voice bandwidth, providing bandwidth measured in the hundreds of kHz and enabling communications at least 100 times faster than that available over pure POTS. allowing you to make phone calls or fax is transmitting or receiving. Let us examine a typical ADSL modem to see how it accomplishes this. A Typical ADSL Transceiver Block Diagram: A Typical ADSL Transceiver Block Diagram ADSL hardware equipments: ADSL hardware equipments DSLAM (Digital Subscriber Line Access Multiplexer) - DSL Access Multiplexer, a mechanism at a phone company's central location that links many customer DSL connections to a single high-speed ATM line. CPE (Customer Premise Equipment) - communications equipment that resides on the customer's premises. For example, DSL modem is Customer Premise Equipment (CPE). The role of the DSLAM: The role of the DSLAM The path of data along the DSL from its commercial or residential source, via the local loop, to the CO (Central Office). The local loop here terminates at the Main Distribution Frame (MDF), to be picked up by one of the CO's many DSL modems. If the form of DSL allows for the carrying of both analog and digital signals, a POTS splitter will separate out the signals. The analog signal will follow its time-honored path along the copper-wire infrastructure. For the digital signal, however, one step before the signal can be shot along to its destination. The roles of the ADSL modem: The roles of the ADSL modem bps - the device sending data to your computer is 2,400 bps, you must receive it at 2,400 bps. Data compression - Some modems perform data compression, which enables them to send data at faster rates. However, the modem at the receiving end must be able to decompress the data using the same compression technique. Flash memory - Some modems come with flash memory rather than conventional ROM, which means that the communications protocols can be easily updated if necessary. An ADSL Network: An ADSL Network Modulations Used in ADSL: Modulations Used in ADSL Modulation is the key of ADSL technology; it is a process in which one signal modifies properties of another. Several modulation technologies are used by various kinds of ADSL. Modulations Used in ADSL 2: Modulations Used in ADSL 2 Discrete Multitone Technology (DMT) Carrierless Amplitude Modulation (CAP) Multiple Virtual Line (MVL) QAM (quadrature amplitude modulation): QAM (quadrature amplitude modulation) A method of combining two amplitude-modulated (AM) signals into a single channel, thereby doubling the effective bandwidth. QAM is used with pulse amplitude modulation (PAM) in digital systems, especially in wireless applications. Discrete Multitone Technology (DMT): Discrete Multitone Technology (DMT) Discrete multitone (DMT) is a method of separating a Digital Subscriber Line (DSL) signal so that the usable frequency range is separated into 256 frequency bands (or channels) of 4.3125 kHz each. DMT uses the fast Fourier transform (FFT) algorithm for modulation and demodulation. Dividing the frequency spectrum into multiple channels allows DMT to work better when AM radio transmitters are present. Within each channel, modulation uses quadratude amplitude modulation (QAM). By varying the number of bits per symbol within a channel, the modem can be rate-adaptive. Carrierless Amplitude Modulation (CAP): Carrierless Amplitude Modulation (CAP) Carrierless Amplitude/Phase Modulation(CAP) is a design of Asymmetric Digital Subscriber Line transceiver developed by Bell Labs. CAP was the first ADSL design to be commercially deployed and, as of August 1996, was installed on more lines than any other. CAP is a variation of Quadrature Amplitude Modulation (QAM), the modulation used by most existing modems in 1997. With CAP, the three channels (POTS, downstream data and upstream data) are supported by splitting the frequency spectrum. Voice occupies the standard 0-4 KHz frequency band, followed by the upstream channel and the high-speed downstream channel. Standards and Interoperability: Standards and Interoperability Standards and Interoperability are the most important of any successful communications technology. The American National Standards Institute (ANSI) has approved DMT as the standard modulation method for Asymmetric Digital Subscriber Loop (ADSL) in 1993. In contrast, CAP remains a single-source proprietary technology that not has been standardized. CAP is a proprietary single-source technology, so interoperability between different chipsets cannot be demonstrated or anticipated. Noise Immunity, and Impulses: Noise Immunity, and Impulses DMT transmitter can easily monitor the channel and then adapt its transmission to the characteristics of the phone line, and continuously updates (bit-swapping) to maintain the optimum. For every line, the DMT system transmits the "best" possible signal. A CAP system cannot modify its transmitter and so it needs to try to undo all the attenuation and notches in one fell swoop at the receiver - a tough challenge. CAP systems are often described in evaluations as not being as robust as DMT systems, or not as tolerant to bridge taps. Error Control: Error Control DMT uses error correction as a potent technique to improve performance and efficiency at low cost; CAP omits it, hurting both performance and inter-operability. The existing CAP chipset only supports error correction on the downstream and the upstream is completely unprotected; the proposed ad hoc report drops even that, so there is no standard defined error correction Performance: Performance DMT is adept at matching its transmission channels to the channel (by varying each of the 200+ tones independently), it is both more efficient in its use of bandwidth than CAP, and delivers higher performance under any realistic circumstance Internet Access : Internet Access DMT is designed for data access; it is a Internet access solution of choice. CAP was a kind solution for video-on-demand, it was initially unsuitable, required a drastic redesign and is still less suited. ADSL Modulation Summary: ADSL Modulation Summary DMT and CAP are two major modulation technologies for the ADSL, but DMT is the most widely used and appears to be becoming the industry standard DMT is adopted internationally by the American National Standards Institute (ANSI), European Telecommunications Standards Institute (ETSI) and the International Telecommunications Union (ITU). DMT has better performance that CAP. DMT is better solution than CAP. Transmission Impairments: Transmission Impairments Every network suffers from impairments; there are three types of transmission impairments Attenuation, Delay Distortion and Noise. Attenuation: Attenuation It is the strength of signal off with distance over any transmission medium. For guided media, this reduction in strength, or attenuation, is generally logarithmic and thus is typically expressed as a constant number of decibels per unit distances. For unguided media, Attenuation is a more complex function of distance and the makeup of the atmosphere. Delay Distortion: Delay Distortion It is a phenomenon peculiar to guided transmission media. The distortion is caused by the fact that the velocity of propagation of a signal through a guided medium varies with frequency. Delay Distortion is particularly critical for digital data. Noise: Noise It is that for any data transmission event, the received signal will consist of the transmitted signal, modified by the various distortions imposed by the transmission system, plus additional unwanted signals that are inserted somewhere between transmission and reception. Impulse Noise Thermal noise Crosstalk Intermodulation noise Thermal noise: Thermal noise results from thermal agitation of electrons in a conductor. Evenly distributed over the entire radio frequency spectrum: white noise. It is present in all electronic devices and transmission media and is a function of temperature In the FM broadcast band where there is no station, the hiss in the background is thethermal noise.Thermal noise cannot be eliminated. Intermodulation noise: Intermodulation noise results when signals of different frequencies share the same transmission medium. It produces signals at a frequency that is the sum or difference of the two original frequencies or multiples of those frequencies. Impulse noise: Impulse noise It is noncontinuous consisting of irregular pulses or noise spikes of shortduration and of relatively high amplitude. It is generated from lightning and faults and flaws in the communications system. Impulse noise is the primary source of error in digital data communication Crosstalk: Crosstalk It is the most important of the capacity limiting noise. It is caused by electromagnetic radiation of other phone lines in close proximity or may be from within the same cable. The crosstalk will decrease as the bandwidth increases. The closer the different wires get to each other the stronger the coupling increases. The crosstalk is typically worse between two pairs in the same binder than in the adjacent binders. The crosstalk transfer function will be different in each pair corresponding to the geometric differences of a binder group. Crosstalk may be minimized by using the twisted pair before twisting the pairs into binder groups. What's special about xDSL?: What's special about xDSL? cables connecting households to phone network are simple twisted pair copper wires.Modem speeds have gradually increased through the use of various compression and other techniques. DSL technology enables much higher speeds,speeds up to 2 Megabits per second - 30 or more times faster DSL has its own kind of "modems". technology allows the network to manage traffic rather than allocating complete end-to-end circuits, user perspective data connection is "always on". xDSL deployment to homes make easier for Internet connections can be sold on a fixed rate "per month" encouraging use of Internet, e-commerce, teleworking etc. Types of xDSL: Types of xDSL ADSL (Asymmetric Digital Subscriber Line) G.Lite or DSL Lite (known as DSL Lite, splitterless ADSL, and Universal ADSL) HDSL (High bit-rate DSL) RADSL (Rate-Adaptive DSL) SDSL (Symmetric DSL) UDSL (Unidirectional DSL) VDSL (Very high data rate DSL) x2/DSL ADSL (Asymmetric Digital Subscriber Line) : ADSL (Asymmetric Digital Subscriber Line) "asymmetric" two-way or duplex bandwidth is devoted to the downstream direction, sending data to the user. small portion of bandwidth is available for upstream or user-interaction messages. most Internet and multi-media need lots of downstream bandwidth 6.1 megabits per second of data can be sent downstream and up to 640 Kbps upstream. high downstream bandwidth means able to bring motion video, audio, and 3-D images to your computer or TV set. G.Lite or DSL Lite (DSL Lite, splitterless ADSL, and Universal ADSL) : G.Lite or DSL Lite (DSL Lite, splitterless ADSL, and Universal ADSL) essentially a slower ADSL that doesn't require splitting of the line at the user end but manages to split it for the user remotely at the telephone company. officially ITU-T standard G-992.2, provides a data rate from 1.544 Mbps to 6 Mpbs downstream and from 128 Kbps to 384 Kbps upstream. expected to become the most widely installed form of DSL. The different DSL technologies: The different DSL technologies HDSL and SDSL are used for symmetric services especially for businesses. ADSL useful for asymmetric service to residential services while VDSL provides the choices for asymmetric or symmetric for business or residential services. VDSL also updated standard for programmable symmetric data rates in the xDSL technologies. DSL technologies still evolving performance of functionality, levels of integration, and speed. A xDSL Summary Table: A xDSL Summary Table ADSL Network Design: ADSL Network Design Design an xDSL Network Design Architecture for the Network Locate residential users by plotting points on the grid Make Assumptions on the Traffic Specification ADSL Network Design Architecture 1: ADSL Network Design Architecture 1 we designed another layer Remote Unit between the CO and end subscribers. This Remote DSL solution is enable service providers to cost effectively extend asymmetric digital subscriber line (ADSL) services to new areas and introduce new high bandwidth premium services. Also provide a low deployment cost for small platforms and facilitate ADSL Network Design Architecture 2: ADSL Network Design Architecture 2 ADSL Network Design Architecture 3: ADSL Network Design Architecture 3 ADSL Network Design Central Office DSLAM Deployment : ADSL Network Design Central Office DSLAM Deployment Description and Assumptions Voice Traffic Specification 1: Description and Assumptions Voice Traffic Specification 1 Phone usage assumptions and measurement Voice Traffic: 0.08 E per subscriber International Calls: 5 % Local calls: 75 % Calls routed to Line Busy: 10 % Calls routed to No answer: 5 % Calls routed to Announcement: 5 % Based on the above usage measurement and assumption the number of voice traffic equipments on the Central office can be calculated Slide46: Description and Assumptions Voice Traffic Specification 2 We have following assumptions DSLAM capacity : 500 subscribers Bandwidth of 1 OC-3 line : 150 Mbps Bandwidth of 1 OC-12 line: 600 Mbps Using this data, we calculate and get result as follow. Effective Bandwidth: d = 1.2 m + 602/c (Ploss=10–9) Description and Assumptions Voice Traffic Specification 3: Description and Assumptions Voice Traffic Specification 3 The assumptions of Internet traffic, file usage, and email usage are shown as table: Network Equipment Specification Voice Equipment Cost : Network Equipment Specification Voice Equipment Cost Line Card Cost : $50 Digitone Receiver: $300 Ringing Circuit: $150 Busy Tone Circuit : $150 Announcement Circuit : $150 Trunk: $200 Switch Port: $50 Central Computer: $250 SLC 96: $100 per line Annual Cost for ADSL provider 1: Annual Cost for ADSL provider 1 DSLAM Chassis Cost: $2500 DSLAM Modem/subscriber: $80 Subscribers / chassis: 64 Number of chassis deployed: 3125 chassis (200K /64) Total number of ADSL ports deployed: 200,000 Total DSLAM Costs: $2500x3125 + $80x200,000 = $238,125,000 Service Aggregation Costs: $20 Annual Cost for ADSL provider 2 : Annual Cost for ADSL provider 2 Total Service Aggregation Cost with Overhead: $4,000,000 Annual Cost per OC3 line: $42,000 Annual Cost per OC12 line: $80,000 Annual Cost per DS1 line: $14,000 Subscribers/DSLAM: 500 Number of OC3s from DSLAM to Multiplexer: 5 Cost of Multiplexer: $1000 Cost of ATM Switch at CO (Cisco LightStream 1010-Supports 8 OC12 lines): $8,000 Monthly expense per customer = Total Annual Costs/(12*X) ADSL Variables and Fault Domains: ADSL Variables and Fault Domains ADSL Future: ADSL Future ADSL is competing with cable-modem, satellite Internet approximately 330,000 households use ADSL in 1999, compared to 1,350,000 households with cable modems. By 2003, IDC estimates cable modems risen to 8,980,000, while DSL risen to 9,300,000 households ADSL is limited (by U.S. Federal Communications Commission regulations) to a maximum of 1.5 megabits per second Current technology can provide a theoretical maximum of up to 7 megabits per second, research promises greater performance with protocols like G.Lite and VDSL ADSL Growth : December 2000 – March 2002 Worldwide DSL subscribers 207.8% Increase in ADSL worldwide ADSL Growth ADSL Residential Subscribers : ADSL Residential Subscribers ‘000 North America 4,267 Latin America 271 Western Europe 3,523 Eastern Europe 32 South and East Asia 374 Asia-Pacific 6,970 Middle East and Africa 37 Total 15473 March 2002 ADSL Business Subscribers : ADSL Business Subscribers ‘000 North America 1,242 Latin America 110 Western Europe 709 Eastern Europe 21 South and East Asia 125 Asia-Pacific 979 Middle East and Africa 11 Total 3,196 March 2002 Percentage Growth By Region : Percentage Growth By Region Region Subscribers (000s) % Growth 2001 2000 188% North America 5510 3397 62% South & East Asia 499 240 107% Asia-Pacific 7949 2986 166% Western Europe 4232 1062 298% Latin America 380 70.1 442% Eastern Europe 53 7.8 579% Middle East & Africa 48 6 700% Total Subscribers: Total Subscribers Conclusion : Conclusion The future looks bright for ADSL. While yesterday's obstacles and negative predictions fade away, many are watching ADSL with renewed interest. The "need for speed" is increasing, and the ADSL industry is working hard to make sure that broadband ADSL continues to be the global choice.