Intoduction

PSTN Course 69572xDSL TechnologyIns. Jamal Kharousheh

Bara Jml Asim ShtayehGroup Members:Mohammad Abu-ObaidIntroduction Bandwidth bottleneck. No question, that's the biggest obstacle. - Bill Gates, Microsoft (from June 1996 Fortune interview)

Incredibly rapid boom of the Internet use and development of on-demand services ---> create solutions that would increase bandwidth, providing faster access to different networks and more efficient use of various applications.

We will talk about one solution, that is

x DSL technology

xDSLDIGITAL SUBSCRIBER LINE xDSL is amodem technology, enabling high-speed delivery of data, audio, and video in a digital form over the existing telephone infrastructure (copper twisted-pair phone lines called the local loop which connects the customer premises and the carriers central office). DSL technologies DSL technologies differ from each other in data rate, operating distance, ratio between downstream and upstream speeds, as well as concerning their applicationsThe basic idea behind all xDSL technologiesThere is a special modem attached to each end of the copper phone line, i.e. one modem at the customer premises and another one at the central office. The phone line is then exploited with the help of advanced modulating techniques. Furthermore, technological advances in digital signal processing, transformers, analog filters and A/D converters contribute to xDSL technologies.Protocols and configurationsBridged networksIn a bridged configuration, the group of subscriber computers effectively connect into a single subnet. used DHCP to provide network details such as the IP address to the subscriber equipment, with authentication via MAC address or an assigned host name

routed networks.use Point-to-Point Protocol (PPP) or Asynchronous Transfer Mode (ATM) (Point-to-Point Protocol over Ethernet (PPPoE) or Point-to-Point Protocol over ATM (PPPoA)), while authenticating with a user id and password and using Point-to-Point Protocol (PPP) mechanisms to provide network details.

Signaling and modulation Transmission methods vary by market, region, carrier, and equipment.

2B1Q: Two-binary, one-quaternary, used for IDSL and HDSL CAP: Carrierless Amplitude Phase Modulation - deprecated in 1996 for ADSL, used for HDSL TC-PAM: Trellis Coded Pulse Amplitude Modulation, used for HDSL2 and SHDSL DMT: Discrete multi-tone modulation, the most numerous kind, also known as OFDM (Orthogonal frequency-division multiplexing)Types of DSL technology Asymmetric Faster downstream rate vs. upstream Suitable for applications such as web-browsing, MP3 downloading, Video on demand (VoD) Symmetric downstream & upstream rates are equal Suitable for office type apps like Video conferencingTypes of symmetric xDSL Symmetric DSL (SDSL) High bit-rate DSL (HDSL) HDSL 2 Single-pair HDSL (SHDSL) ISDN DSL (ISDL) DSL over ISDNHDSL - High data rate Digital Subscriber Line

Fully standardized by ANSI (American National Standards Institute) and ETSI (European Technical Standards Institute).

HDSL requires two twisted pair lines to carry data at a rate of 1.544 Mbps both upstream and downstream. Another alternative of HDSL technology uses three twisted-pair copper lines to carry 2.048 Mbps. These data rates are provided as far as 12,000 feet (3.6 Km).

HDSL ApplicationsHDSL technology is mainly used by early adopters in a restricted area (such as student living in a campus area) as well as by private organizations, as it demands two or three twisted pair copper lines. Typical applications of HDSL include access to the following systems: PBX network, cellular antenna stations, digital loop carrier systems, inter-exchange POPs, Internet servers and private data networksSDSLSingle line Digital Subscriber LineSDSL has the ability of transferring data at the same speed as HDSL, but it requires only one twisted-pair copper wire. Additionally, POTS (Plain Old Telephone System) and digital data transfer can occur simultaneously on SDSL.

The operating distance of SDSL is only 10,000 feet (3Km).

SDSL ApplicationsTypical SDSL applications are the same than supported by HDSL. However, SDSL has one important advantage over HDSL: it is also suitable for residential users, as they usually have only a single telephone line.

Types of asymmetric xDSLAsymmetric DSL (ADSL)

Very High Bit-rate DSL (VDSL)

Rate-Adaptive DSL (RADSL)

ADSLAsymmetric Digital Subscriber LineADSLApprox. 90 -100 KByte/sec

Voice-Band-Modem V.90Approx. 5.7 KByte/sec!16What does ADSL meanAsymmetric: The data can flow faster in one direction than the other. Data transmission has Faster Downstream to the subscriber than upstream.Digital: No type of communication is transferred in an Analog method.All data is Purely Digital, and only at the end, modulated to be carried over the line. Subscriber Line: The data is carried over a Single Twisted Pair copper loop to the subscriber premises.17IntroductionADSL is a form of DSL, a data communications technology that enables Faster data transmission Over Copper telephone lines than a conventional Voice-band-Modem can provide.ADSL is capable of providing up to 50 Mbps, and supports voice, video and data.Applications that demand a Higher Data Rate DL than UL.With ADSL the Signal Coupling is reduced and a Higher Data Rate and a Longer Distance Can Be Achieved.ADSL is the #1 Broadband Choice in the World with over 60% market share.ADSL is now available in every region of the world.18ADSL standards :Standard name Common name Downstream rate Upstream rate ITU G.992.1 ADSL (G.DMT) 8 Mbit/s 1.0 Mbit/s ITU G.992.2 ADSL Lite (G.Lite) 1.5 Mbit/s 0.5 Mbit/s ITU G.992.3/4 ADSL2 12 Mbit/s 1.0 Mbit/s ITU G.992.3/4 Annex J ADSL2 12 Mbit/s 3.5 Mbit/s ITU G.992.3/4 Annex LRE-ADSL2 5 Mbit/s 0.8 Mbit/s ITU G.992.5 ADSL2+ 24 Mbit/s 1.0 Mbit/s ITU G.992.5 Annex LRE-ADSL2+ 24 Mbit/s 1.0 Mbit/s ITU G.992.5 Annex M ADSL2+ 28 Mbit/s 3.5 Mbit/s 19ISDNADSL

FTTx VDSL2ADSL2plus

Enhanced CopperHybrid Fibre/CopperPure Fibre

ADSL Speed ComparisonVoice band ModemFTTHCopperCopper20

ADSL Loop ArchitectureISPCentral OfficeSubscriber PremisesVoice Switch DSLADSL network components

(ATU-R): The ADSL modem at the customer premises.(ATU-C): The modem of the central office.(DSLAM): DSL access multiplexer.(BAS): Broadband Access Server.Splitter: an electronic low pass filter that separates the analogue voice or ISDN signal from ADSL data frequencies DSLAM. 21ADSL Subscriber RequirementsPhone-line activated by your phone company for ADSL.Filter to separate the phone signal from the Internet signal.ADSL modem.Subscription with an ISP supporting ADSL.

22Spectrum of local telephone lineDSL technologies use also other frequencies outside the voice band to modulate information on your local telephone line.ISDN provides you with a 160 kbps connection on your local line.ADSL provides you a high speed connection on your local line.

Voice-band-Modem V.90 technology is able to accelerate data downstream from the Internet to your computer at speeds of up to 56Kbps.The solution to this problem is ADSL, where we extend the used frequency band to about 1MHZ.Using ADSL downstream, data speeds up to 8,1 Mbps are possible.The maximum upstream speeds is limited to about 1/10 of the maximum downstream speed.The distance is however limited to 5,4 km.ADSL offers the opportunity to run multiple services at the same time: voice, surfing the web23ADSL SpectrumADSL uses frequencies on the local line up to 1,1MHz.These frequencies do NOT overlap with the POTS band and is so allowing simultaneous voice communication.

We introduce the concept of FDM (Frequency Division Multiplexing).Apart from the traditionally used frequencies over the UTP (300 - 3400 Hz), we start using higher frequencies for the ADSL upstream and downstream channel.As ADSL is an asymmetrical service with more capacity in the downstream direction, we need more frequencies in this direction.It will be explained that the highest frequencies result in problems. The capacity of transporting data decreases with the increase of the used frequencies. In other words it is a pity that the frequencies reserved for POTS cannot be used for ADSL. POTS frequencies cannot be used for ADSL since the Life Line concept is still valid. The latter means that one should be able to make a phone call in case of a power failure.VoDSL (making phone calls over the ADSL signal) does not support this Life Line concept.ADSL speeds would increase when ACTIVE filters (splitters) were used. Because of the Life Line concept only PASSIVE are allowed since the active splitters contain Op-Amps that need to be powered.The lower frequencies used by ADSL can disturb the audible spectrum and need to be filtered out towards the telephone set.With on-hook and off-hook situations of your telephone the line impedance changes which will have an impact on the ADSL modem communication.Voice & data are transported over the same copper wire simultaneously in both directions (full duplex).The ADSL signals travel between the Central Office (CO) and the ANT (ADSL Network Termination).A wide range of filters/splitters is available on the market today adapted to local situations. From country to country complex impedances can differ as also the physical presentation of the local line.24ADSL SpectrumThe spectrum used for ADSL is divided into 255 carriers. Each carrier is situated at n x 4,3125 kHz.For the upstream direction carriers 7 to 29 are used.For the downstream direction carriers 38 to 255 are used.On each carrier the SNR is measured and the QAM determined.Minimum QAM-4 : 2bits/symbolMaximum QAM-16384 : 14 bits/symbolSymbol period for each carrier : 250 s

25Discrete Multi Tone (DMT)

For ADSL, multiple carrier frequencies are modulated on the ADSL line using QAM (Quadrature Amplitude Modulation).QAM is a modulation technique where both amplitude and phase are modified.The amount of bits we can put on one symbol depends on the amount of amplitude and phase levels we distinguish.SNR is measured to determine the maximum achievable QAM.On each carrier the SNR is measured and the QAM determined.Minimum QAM-4 : 2bits/symbolMaximum QAM-16384 : 14 bits/symbolThe sum of all frequencies is put on the lineThis principle is called Discrete Multi Tone (DMT)26Voice/Data over DSL

In ADSL the voice is send in a separate part of the spectrum (FDM). The disadvantage is the need of a Pots Splitter and the fact that you have only one line.In the case of VoDSL the telephones (up to 16 ) are connected to the VoDSL modem and the voice is multiplexed on an ATM connection over ADSL. All 16 phones can be used at the same time for different calls.VoDSL modems these days implement 4 or 8 telephone ports.The limitation of 16 is due to the limitation of the upstream ADSL bitrate. In the case of SHDSL the number of phones could be increased up to 32.

In the way the voice and the data traffic are combined. This is voice / data convergence in the access network only.In most countries local regulations imply that the lifeline service must be available at all times. As our ADSL modem is locally powered a power outage will result in loss of our ADSL connection. This means that we will still need our POTS service even with VoDSL. At the moment R&D centers are looking at remote powering the ADSL modem so that ADSL would keep functioning and VoDSL is still possible. This will then make our POTS band dispensable meaning we would also be able to use those frequencies for xDSL communication.27ADSL Speed FactorsThe Distance from the local exchange.

The Type and Thickness of Wires used.

The Number and Type of Joins in the wire.

The Proximity of the wire to Other Wires carrying ADSL, ISDN and other non-voice signals.

The Proximity of the wires to Radio transmitters.

28ADSL RangeIn general, the maximum range for DSL without a repeater is 5.5 km. As distance decreases toward the telephone company office, the data rate increases.

For larger distances, you may be able to have DSL if your phone company has extended the local loop with optical fiber cable.Data RateWire gaugeWire sizeDistance1.5 or 2 Mbps24 AWG0.5 mm5.5 km1.5 or 2 Mbps26 AWG0.4 mm4.6 km6.1 Mbps24 AWG0.5 mm3.7 km1.5 or 2 Mbps26 AWG0.4 mm2.729Capacity of the Channel

The maximum attainable data speed depends on the signal to noise ratio (SNR).The higher the (allowable) signal strength, and the lower the amount of noise on the line, the higher the capacity.Unfortunately a lower noise level requires high quality lines which are expensive or not available.On the other hand the signal strength is limited (governmental constraints) in order to limit the amount of crosstalk.A decreasing signal to noise ratio will result in more bit errors (BER) on the line but with current technologies it is possible to detect AND correct these errors up to a certain level. It can be said that by introducing these error detection/correction mechanisms we can actually increase the capacity of the line for a certain SNR and BER.30Capacity Vs. Distance

The figure illustrates the distance dependency of the Shannon/Hartley capacity theorem.

Since the attenuation (signal loss) increases with distance (cable length) the maximum data speed drops with the distance.

Theoretically ADSL can reach a downstream capacity of apc. 15Mbps at 0km. Although in practice this is limited to 8,1Mbps31Atten. Vs. Freq.

The signal strength is not only distance dependent.It is also frequency dependent. This is due to the skin effect.

R =( x d)/SeffR = resistance () = resistivity (.m) d = distance, length of conductor (m)Seff = effective cross sectional area of conductor (m2)32

Attenuation due to distance Local exchangeUnshielded Twisted Pair 0,5 mm24 km : loss of 32dB at 150 kHz

Transmitted PulseReceived Pulse5 km : loss of 55dB at 150 kHz

The Importance of a TwistReduce : Crosstalk, RFI and EMI.

What means a loss of 32 dB at 150 kHz?Attenuation (dB) = 10 x log10 (P1/P2) P1/P2 = Inv log10 (Attenuation / 10) P1/P2 = Inv log10 (32 / 10) = 1585this means that our received pulse is 1585 times smaller !!What means a loss of 55 dB at 150 kHz?Attenuation (dB) = 10 x log10 (P1/P2) P1/P2 = Inv log10 (Attenuation / 10) P1/P2 = Inv log10 (55 / 10) = 316228this means that our received pulse is 316228 times smaller !!

33Speed Vs. Distance

Higher frequencies suffer more from attenuation than lower ones, since the skin effect has more impact on the higher frequencies.

That is why the upstream signal is less attenuated than the downstream channel.

34Crosstalk

A telephone cable contains up to several thousand separate wire pairs packed closely together. The electrical signals in a wire pair generates a small electromagnetic field, which surrounds the wire pair and induces an electrical signal into nearby wire pairs. The twisting of the wire pairs reduces this inductive coupling (also known as crosstalk), but some sigmal leakage remains.NEXT (near end crosstalk) is a major impairment for systems that share the same frequency band for upstream and downstream transmission. NEXT noise is seen by the receiver located at the same end of the cable as the transmitter that is the noise source. In other words NEXT means that the receiver of one twisted pair picks up noise transmitted (by the transmitter) another one.

Transmission systems can avoid NEXT by using different frequency bands for upstream and downstream transmission. FDM (Frequency Division Multiplexed) systems avoid NEXT from like systems (also known as self NEXT). FDM systems still must cope with NEXT from other type of systems that transmit in the same frequency band, and other phenomenon known as FEXT (far end crosstalk).FEXT is the noise detected by the receiver located at the far end of the cable from the transmitter that is the noise source. FEXT is less severe than NEXT because the FEXT noise is attenuated by traversing the full length of the cable.A major advantage of fibre optic transmission is the lack of any crosstalk.Conclusion: NEXT is worse than FEXT for systems sharing the same frequency band in the up and downstream direction. Alcatel ADSL uses FDM and thus avoids NEXT. Here FEXT becomes the critical impairment.When ADSL is mixed with other systems in the same cable then NEXT can occur because of overlapping frequency ranges! (see next slide)35When AoP (ADSL over POTS) and AoI (ADSL over ISDN ) reside in the same cable there is NEXT.Some frequencies of the downstream transmitter of an AoP line overlap with the receiver frequencies of an AoI line.Near End Crosstalk

ADSL over an ISDN line uses another spectrum than ADSL over a POTS line. When both systems are used within the same bundle of a cable Near End Crosstalk (NEXT) will occur.36Bridged Taps

In some countries it is common practice of splicing a branching connection (bridged tap) onto a cable. Thus a bridged tap is a length of wire pair that is connected to a loop at one end and is unterminated at the other end. Approximately 80% of loops in the US have bridged taps; sometimes several bridged taps exist on a loop. One reason for a bridged tap is that it permits all the pairs in a cable to be used or reused to serve any customer along the cable route.The reflection of signals from the unterminated bridged taps results in signal loss and distortion.When (subscriber #3) is asking for phone call service a main cable is put in the ground.Later on when (subscriber #2) and (subscriber #1) ask the same thing a lateral is drawn from the main cable.

Imagine (subscriber #2) decides left home and travel, thus he cuts the lateral. Since there is no longer a telephone connected to the lateral there is no nice power sdissipation anymore. This results in reflections; reflections that travel in both directions of the main cable.37VDSLVery High Bit-rate DSLVDSL is next generationDSLStandard G.993.1 by ITU VDSL transfers asymmetric data at rates much higher than ADSL, but over much shorter lines.Using the frequency band from 25 KHzto 12MHz.The maximum downstream speed of 51.84 Mbps can be reached only if the copper wire is max. 300 m long. With a distance of 1.3 Km, the data rate is 12.96 Mbps. The corresponding upstream rates are 2.3 Mbps and 1.6 Mbps respectively.

VDSL General Model

ONU: Optical Network Unit NT: Network Termination Duplexing methodsystems use four-band plan that start at 138 kHz and extends up to 12 MHz.Band from f0 to f1 (25 kHz and 138 kHz) optional band, could be up or down stream

Transmission power The transmitted Power Spectral Density shall be calculated as the following :

kl0: electrical length of lineThe LOSS function is an approximation of the loop attenuationReturn loss

RV (terminal equipment resistance) for VDSL band test shall be pure resistive 100 .

InterleavingInterleaving shall be used to protect the data against bursts of errors by spreading the errors over a number of codewords.It shall be possible to adjust the interleave depth via the management system to meet latency requirements.

Where & What can VDSL provideLarge BusinessesVideo conferencing and VoIPVideo on demandVDSL technology could also be deployed in High Definition TV (HDTV).VDSL is expected to be future residential access technology that supports similar applications than ADSL.

VDSL is still under development, and it is viewed that in the future VDSL might achieve the same data rates both downstream and upstream, but at a shorter distance.

There are no general standards for VDSL yet, but several standards organizations and forums are currently working on the standardization of VDSL.FTTH (Fiber To The Home) this is a solution for many obstacles such as long distances limitation, cross-talk, and power loss. VDSL What's Next? RADSL - Rate adaptive DSLRDSL is a rate adaptive xDSL technology, which means that it can work at different data rates depending on the length of the line and thus, it can overcome the distance limitations for xDSL to a certain extent.

RADSL ApplicationsRADSL allows speed adjustment according to the line quality. It enables carriers to serve users who reside a long way from the nearest central office. A remote user may not get the fastest speed because of the distance of the line, he will, however, get the best possible rate. Thus, RASDL can basically support all the same services supported by DSL, HDSL and ADSL depending on the line distance.Needs dedicated modems.

xDSL Alternatives Internet over Cable TV (CATV) :

CATVThis technology uses the Cable TV infrastructure

Cable and DSL are the two big rivals in the world of broadband. Cable isn't limited by distance like DSL , signal strengths don't weaken over long distances.Distance up to 50 KmDownstream: 40 Mbps / Upstream: 20 Mbps While DSL allows you to use the telephone and Internet simultaneously, cable lets users watch television and surf the Internet at the same time

Internet and digital telephone on one bill. Cable and DSL speeds are about the same.

The one disadvantage with cable is bandwidth -- connection speeds can slow down if too many people are using a cable service at the same time(bandwidth is shared among all subscribers)

CATVxDSL AlternativesWiMax

A new technology, known as WiMax or 802.16, looks to combine the benefits of broadband and wireless. WiMax will provide high-speed wireless Internet over very long distances and will most likely provide access to large areas such as cities. WiMax technology was available in most American cities in 2008 and until now it`s forbidden in Palestine .

Thank You For Your AttentionWe will be glad to answer any Question

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