7/2/2016
`1. Kitz - ADSL Technology & DMT- Bit Allocation + Bit Swapping.::
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`
`
`This tutorial is aimed at those that wish to know more about the technology behind ADSL and howit is
`possible to transmit digital data over the telephone line between our home and the exchange.
`Unlike cable broadband which uses specially laid optical fibre to the premises and formspartof a
`larger network, ADSLutilises existing telephone cable to bring broadband to the home.
`
`How doesadsl work- on theline.
`Whatis modulation?
`Whatis DMT?
`How does DMT work?
`Whatfrequencies are used?
`VDSL2 tones in use.
`Tones which aren't in use.
`Whatare Tones,carriers, buckets, bins?
`Initialisation and Synchronisation
`Bit Loading
`Bit Allocation
`Bit Allocation Table
`Whatis Bit Swapping?
`Whatis Bit Error Rate (BER)?
`Bit Allocation and Power Cut Back
`Bit Allocation and Low SNR
`Bit Allocation and Long Lines
`What is Seamless Rate Adaption (SRA)?
`
`
`
`~ How does adsl work- 'on theline’.
`
`Telephone lines can be used to convey analogue signals and the copperpair has the ability to carry a
`range of frequencies. DSL makes use of the fact that voice signals for telephone devices are all under
`4kHz, and utilises the previously unused higher frequencies to transmit data.
`
`Anadsl splitter is used in the home to separate the telephony and adsl signals and to help
`
`ensure that telephony devices don't use any of the frequencies used by ADSL.
`
`e ADSL1 and ADSL2utilise frequencies up to 1.1 MHz
`e ADSL2+ utilises frequencies up to 2.2 MHz
`¢ VDSL2 utilises frequencies up to 17.664 MHz
`
`DSL uses a technology called Frequency Division Multiplexing (FDM) which meansit
`combines multiple frequency signals onto a single carrier wave over a shared medium
`suchas cable, wire or fibre.
`
`Several years ago it was not unusual to hear BT engineers refer to DSLAMsat the
`exchange as a "Mux" or Multiplexor - DSLAM stands for Digital Subscriber Line Access
`Multiplexer.
`
`
`
`Top |
`
`« Whatis Modulation?
`
`Because our computers use digital data a MODEM (MOdulator-DEModulator) is needed to
`code and decode between digital and analogue signals. The method of converting digital
`data into analogue signals which can be carried over the copper wire is known as
`Modulation.
`
`Our modem/routers and the DSLAM at the exchange are the hardware equipment that perform
`modulation.
`
`There are different methods of modulation, but the common standard used for ADSL is called DMT.
`Variations on the basic DMT modulation may be used depending uponthe adsl type, but the basic
`
`http:/www.kitz.co.uk/adsl/ads|_technology.htm
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`Dish
`Exhibit 1033, Page 1
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`Dish
`Exhibit 1033, Page 1
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`7/2/2016
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`
`1. Kitz - ADSL Technology & DMT- Bit Allocation + Bit Swapping.::
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`theory remains the same.
`
`G.992.1
`
`ADSL2
`
`|G.992.3
`
`DMTstandard for adsl1
`Improved modulation method with flexible framing and optimised use of RS
`
`|g.DMT.bis
`
`|coding gain within the frame structure. Enhanced channel overhead
`
`
`
`Type_[Standard
`
`configuration.
`Doubling channels available for use.
`992.5
`G.993.2|—_—[ Extensions: G.INP = G.998.4 Vectoring = G.993.5
`
`Top |
`
`« What is DMT?
`
`DMT(Discrete Multi Tone) is a method of converting digital data into tones or frequencies that can be
`carried over telephone wire. Called 'Multi-tone' because it splits the available frequencies into a defined
`number of smaller sub-channels or tones and 'Discrete' from the mathematical term meaning distinct
`ar cansarata
`
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`fLearn more
`
`Close message
`
`. VDSL2 (profile17a)has4096sub-channels
`DMT deploys many ''virtual modems" which are responsible for the control of each sub-channel. These
`virtual modems all work in tandem to carry the data bitstream.
`
`DMTis a modulation method for Frequency Division Multiplexing (FDM) which is when multiple signals
`are combined and carried over the same medium.
`
`Top ff
`
`~ How does DMT work?
`
`DMT makesuse ofthe available frequencies that can be transmitted on the telephoneline and splits
`them into 256/512 equal sized frequency bins of 4.3125 kHz each.
`
`Sub-channels (or carrier bins) are where data bits are transmitted to and from our modem. Each sub-
`channel within a specific frequency range will be responsible for either upstream or downstream data.
`
`PSTN
`
`Upstream
`
`ADSL Frequencies
`Downstream
`
`
`t—t—+4
`+—+
`>
`30064
`25
`138 142
`1104
`Hz kHz
`kHz
`kHz kHz
`kHz
`
`e Each carrier bin of 4.3125 kHz is the tone that you may see recorded on some routerstats or in
`DMTtool.
`e« You mayalso see sub-channels referred to as carriers, bins or buckets because this is what
`carries the data bits within each frequency range.
`e The full frequency range is split - regardless if you can make use of those frequencies or not.
`
`Not all channels are actually usable for the transmission of data. Some tones are not used such as the
`pilot tone, whilst some tones are reserved for voice or to prevent overlap of the different signal types.
`
`e« Some tones, particularly the higher frequency ones may not be notbe in use on longer lines due
`to the signal strength at that frequency being too weak.
`
`It may help you visualise how DMT worksif you imagine this scenario:
`Imagine an old 56k modem that worked on the voice band frequency of 0-4kHz.
`Now imaginelots of 'virtual' 56k modems each working on their own frequency each giving you 56kbps. As well
`as splitting the available frequencies, DMT is responsible for 'binding' all these 'virtual modems' together.
`ADSL(1&2) has a maximum available 223 downstream subchannels. 223 x 56kbps = 12Mbps.
`ADSL2+ doubles the amountof available frequencies (subchannels) and we get 24Mbps.
`
`DMTis the technology which divides the whole bandwidth on the telephone line into lots of sub-
`channels and then controlling these 'virtual modems' as one together in order to get higher speeds.
`
`
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`http:/www.kitz.co.uk/adsl/ads|_technology.htm
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`2/8
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`Dish
`Exhibit 1033, Page 2
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`Dish
`Exhibit 1033, Page 2
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`

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`7/2/2016
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`1. Kitz - ADSL Technology & DMT- Bit Allocation + Bit Swapping.::
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`Top ff
`
`« Whatfrequencies are used?
`
`Below is a chart showing the available frequencies and corresponding frequency tones for various adsl
`standards.
`
`ADSL
`Type
`
`ADSL
`Standard
`
`Speed
`Up to
`
`Maximum
`Frequency
`
`[Upstream /Upstream /Downstream |Downstream
`[Start
`Tones
`Start
`Tones
`
`Total
`BINs
`
`60-511
`
`The calculator on the right will help convert tones into the
`frequencythat it is centered at.
`
` DSL Frequency Bins & Tones
`Tone
`Bin
`Frequency
`an
`aan ie
`tae
`
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`
`Closemessaae|
`
`33-255
`142.3 kHz
`aDsL1__|G.992.1
`
`
`IADSL2—|G.992.3 12 Mbps [1.1 MHz 25 kHz 142.3 kHz 33-255
`
`
`
`ADSL2+ _|G.992.5
`
`AnnexM_|(incr25 kHz|6-56 [258 khzupstream) _|24 Mbps_[2.2 MHz
`
`
`
`
`
`
`VDSL2 BandPlans in the UK
`|
`one Set
`esate]team|owen
`Band|uo|FaneKromporantorammt
`
`jCabinet|
`
`[Huawei?)_—«iB2_~~—=«iB7i —=séik205—=st972 ~—=séeve2 «Bs —~«B59—=séi2i6 —*fsea
`
`pcBocm)|
`[|ecr6Bi82 —‘fii93—fi984_—se770~—«#B3SsB57 Ss—f1959
`
`Top |
`
`~ VDSL2 Tonesin use.
`
`|
`
`Convert
`
`|
`
`The following tones are in use for VDSL2 FTTC in the UK. The ECI and Huawei cabs haveslightly
`different band plans:
`
`|cFTN)Jo
`
`Top
`
`~ Tones which aren't in use.
`
`Certain sub carrier channels are not used. Some of these are laid down in the g.DMT standard, whilst
`some others may depend upon the DSLAM/MSAN manufacturer and varyslightly.
`Common tonesnotin use are:-
`
`DC(First Tone). Tone 0.
`e
`e Guard Band(Tones 1 to 5 < 25.875 kHz). Tone 1 POTs. Tones 2-5 prevents cross talk between POTs + adsl.
`e Guard Band (Tone 32 - 138kHz). Prevents cross talk between upstream and downstream data.
`¢ Nyquist frequency(Final frequency tone)
`e Upstream Pilot Tone. (Tone 16 - 69kHz)
`*« Downstream Pilot Tone. (Tone 64 - 276kHz).
`e Adaptive Pilot Tone. (Some adsi2+ systems select best channel conditions for pilot. Often tone 105, 110 etc)
`e« Annex_M Stop Band. (Tone 59 - 254kHz). ADSL2+ Annex_M only.
`¢ DSLAM Specific Tones (eg Tones 476 - 499 2053kHz-2156kHz on Be*/02 MSANsonly).
`
`Your router will also mark any sub-channels where the SNR is too low to carry data as unusable.
`
`Top |
`
`~ Tones, carriers, buckets, frequency bins
`
`Generally all of the above terms may be used interchangeably, but to recap and clarify a bit further:
`
`http:/www.kitz.co.uk/adsl/ads|_technology.htm
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`3/8
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`Dish
`Exhibit 1033, Page 3
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`Dish
`Exhibit 1033, Page 3
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`

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`7/2/2016
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`1. Kitz - ADSL Technology & DMT- Bit Allocation + Bit Swapping.::
`Frequency
`The whole available frequency bandis split into a
`distinct number of sub-channels.
`301875
`25.875
`kHz
`With adsl over POTs, the sub-channels form 3
`\
`\
`distinct separate channels:
`Bin / Bucket
`
`
`~ Voice
`
`containing
`|
`!
`omit
`ining
`1ov10110
`
`data bits
`;
`:
`
`Tone #
`
`~ Upstream
`~ Downstream
`
`6
`
`e Sub channels mayalso be referred to as carriers, bins or buckets - so called because they are
`used to carry data bits.
`e Each sub-channel has the same amount of bandwidth (4.3125 kHz) but transmits on different
`frequencies.
`e The tone relates to the frequency on whichthesignal is transmitted.
`e Each toneis centered on a specific frequency at whichit transmits.
`e¢ The amountof data bits that can be carried in the bin can vary depending uponthe quality of the
`signal at the particular frequency range for that particular bin.
`
`Top ff
`
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`sustain.
`
`exchange and sync speed is the rate at whichit is agreed that yourline can
`
`On the rate adaptive products before your router is said to be in sync it must
`go through a processcalled initialisation to set up the sync speed. Initialisation
`consists of four key stages:
`
`
`seers
`
`| < 3
`
`@
`448 kbps
`
`|
`
`¢ Handshake- Basically saying 'hello can you hear me' and giving details of which technology is
`to be used (adsl 1, adsl 2 etc) and which protocols are to be used.
`Depending upon the technology the number of available subchannels are determined as per the
`defined standard (G.992.1 G.992.3 etc) The DSLAM will define which sub-channels may be used -
`for example certain tones are deliberately not used.
`¢ Transceiver Training - Preliminary estimation of loop attenuation, test datastream, reporting of
`upstream power levels, power level adjustment (cut-back) if needed for spectral masks. Some
`sub-channels may have masks applied which limit the maximum power level at a particular
`frequency in order to reduce the risk of cross-talk.
`e Channel Analysis - The modem will respond and the condition of each sub-channel is analysed.
`Power levels are reported and SNR and attenuation is calculated. Depending upon the condition
`(Noise/power level) of each channel, this determines the amountof data bits that can be carried
`in each channel. See Bit Loading for more information about this stage.
`e Exchange - Setting the sync speed. The amount of overall bits that can be carried acrossall the
`sub-channels will determine your sync speed. (See Bit Allocation). The dslam will check that the
`modem can receive data at that speed ok and the router should respond and synchronisation is
`attained. If not the initialisation process is repeated until sync is achieved.
`
`Top ff
`
`~ Bit Loading
`
`The amountof bits that can be carried per channel depends upon the SNR at that particular frequency,
`lower SNR levels may need more power to transmit data and since each frequency is subject to an
`overall powerlimit, those frequencies are able to carry less bits than a channel with a better SNR.
`
`e
`e
`
`e The better the SNR at that frequencies in the sub-channel range, then the morebits that can be
`allocated to that particular carrier bin.
`If the signal is good then 15 bits (maximum) can be allocated to that tone.
`If the SNR is weak/weaker at a particular frequency range, then not as manybits can be carried
`by the tone.
`e Each 3dB of SNR equatesto 1 bit (of data),
`A minimum of 2 bits per bin is needed for the tone to be usable for ADSL1 (6dB)
`ADSL2 and ADSL 2+ supportsingle bit tones (3dB).
`If there's insufficient SNR in the channel, then the carrier bin is marked by the router as
`unusable.
`
`e
`
`Bits are encoded as a constellation QAM (Quadrature Amplitude Modulation) which transmit the data by
`modulating the amplitude of 2 carrier waves. Called Quadrature since the 2 waveforms are out of
`phase by 90 degrees.
`
`The higher frequencies tend to carry less bits purely because the SNR isn't as good for those channels.
`Higher frequencies are morelikely to be attenuated, therefore the SNR isn't as good and
`consequentially the carrier bins for those tones cant carry as many databits.
`
`http:/www.kitz.co.uk/adsl/ads|_technology.htm
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`4/8
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`Dish
`Exhibit 1033, Page 4
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`Dish
`Exhibit 1033, Page 4
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`

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`1. Kitz - ADSL Technology & DMT- Bit Allocation + Bit Swapping.::
`With rate adaptive dsl, its the SNR of the sub-channels which will determine your sync speed not the
`frequency of the tone. As long as the SNR at that particular frequency is good then modulation will
`load x no of bits to the bin regardless if its a high or low frequency.
`Lines which are more attenuated will see SNR decrease morerapidly at the higher frequencies hence
`less bit allocation overall and a lower sync speed.
`
`Top |
`
`DMT Bit Allocation
`
`
`
`
`
`
`Bits
`
`
`
`
`Tone
`192
`193
`194
`195
`196
`197
`
`Freq kHz) 826|832.3|836.6|840.9|645.2|849.5
`Skitz 2005
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`7/2/2016
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`Cookies help us deliver our services. By using our services, you agree to our use of cookies.
`
`fLearn more
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`Close message
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`As an example:
`
`Say you have a bin at tone 192 @ 828kHz that has an SNR of say 50dB, then that's more
`than enough SNRto allocate the full 15 bits to the carrier.
`Now say at tone 194 @ 836kHz, there's some noise broadcasting at that same frequency
`which takes the SNR down to 25dB, then only 5 bits may be able to be encoded on that
`channel.
`But frequency bands slightly further up may be fine and back up at 50dB SNR so 15 data
`bits are encoded onthattone.
`
`Bit Allocation is not actually quite as straight forward as in the above example and there's moretoit
`during the sync negotiation period which has to cover an allowance for errors as defined by the Bit
`Error Rate (BER) and involvesa fairly complicated process called Quadrature Amplitude Modulation
`(QAM) which is beyond the scope of this tutorial, and this is what determines the final sync speed.
`Somewherein that process is the required overhead for Interleaving and/or more correctly Error
`Correction, and of course the Target SNR which sets some sort of base line, but...
`
`e The QAMrate is said to be 4,000 symbols per second, therefore each 3dB of SNR available in the
`sub channel over the base line will give approx 4kbps of sync speed, subject to a maximum of
`60kbps (15 x 4kbps) per carrier.
`e Sync rate depends on the number of bits loaded. With adsl each 3db of SNR is worth anywhere
`between 400 to 1200kbps of speed.
`e VDSL uses higher frequencies and has more available tones for loading. A rough guideis :
`~ Sync speeds of around 20Mbps - each 3dB is worth 3Mbps
`~ Sync speeds of around 40Mbps - each 3dB is worth 6Mbps
`~ Sync speeds of 60Mbps or more - each 3dB is worth 11Mbps.
`
`Top ff
`
`~ Bit Allocation Table
`
`Once a line has sync'd a Bit Allocation Table (BAT) is defined which is what specifies how manybits are
`used/can be used within the sub-carrier channel.
`All modem routers will maintain a Bit Allocation Table and some routers allow you to view the Bit
`Allocation Table which may be useful for diagnostics.
`
`Top
`
`~ Bit Swapping
`
`Bit Swapping is a way of keeping the line more stable by constantly monitoring the frequency bins
`(carriers) in use and reusing them if possible.
`
`The bit swap process enables the connection to either change the
`number of bits assigned to each individual subchannel orif
`necessary increase the powerlevel (gain) whilst still maintaining
`the data flow.
`
`http:/www.kitz.co.uk/adsl/ads|_technology.htm
`
`Dish
`Exhibit 1033, Page 5
`
`Dish
`Exhibit 1033, Page 5
`
`

`

`1. Kitz - ADSL Technology & DMT- Bit Allocation + Bit Swapping.::
`
`If after sync the SNR within a specific tone falls too low to transmit Bit Swapping Process
`x no of bits, then bit swapping allows any ‘spare’ in other sub
`1. Bit Allocation
`channels to be used, whilst still maintaining the same number of
`total bits in the Bit Allocation Table.
`
`of 2 bits = 6dB of SNR to be usable for adsl1 or 3dB for adsl2/2+. 10 11 12 13 14 15 16 17 18 19
`
`
`
`There's a minimum amountof bits in a channel.. and if the bits fall
`too low (say if you had a quick noise burst at a certain frequency)
`then the router could mark that channel as unusable which may
`cause the line to lose connection. A carrier bin needs a minimum
`
`With bit swapping the router can swap the bits around and
`redistribute the bits to other channels by using any spare SNR at
`other frequencies or increasing the gain.
`
`Without bit-swapping, your connection would lose sync every time
`there was a noise burst that meant any sub-channel wasn't able to
`transmit its allocated numberofbits.
`
`Ton f
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`Tene
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`®Shhz 2008
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`2 &
`&4
`2
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`7/2/2016
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`~ Bit Error Rate (BER)
`
`The Bit Error Rate is calculated as the percentage of transmitted bits which contain errors. Many
`routers have the ability to conduct a Bit Error Rate Test (BERT). For the duration of the test the router
`will count the number of bits transmitted which is divided by the number of erroneousbits.
`
`The result may be displayed as a figure with 10 to a negative power for example 107” which is
`0.0000001 or 1e-7. To put it simply a BER of 10-®is one errored bit in every 1,000,000 bits
`transmitted.
`
`The standard allowance for Bit Error Rate in adsl is a BER of 10-7. The SNR margin is calculated as
`SNR minus an allowance for a 1077 BER.
`
`During a BERtest, if the router is measuring CRCs in the FAST path bit stream , then 1 CRCis the
`equivalent of 20 bit errors and 50 bits for interleaved path.
`
`Top |
`
`~ Bit Allocation and Power Cut Back
`
`Below is an example of a healthy line showing the Bit Allocation Table and SNR statistics from a router
`with the aid of DMT tool.
`
`i104 &
`
`Ei]
`
`72
`
`bo]
`
`104
`
`1 6152)
`
`(168
`
`O14 2G 22 Tone
`
`24
`
`« Notice how the shape of the Bit Allocation (blue lines) correlate to the SNR (greylines) in the
`lower table. The yellow lines show the SNR Margin.
`e Also note the smooth curves at on the upstream causing a inverted 'U' and also at the beginning
`of the downstream. This is likely due to spectral masks applied at the DSLAM which ensuresthat
`power levels are cut back to reduce thelikely hood of cross-talk on those frequencies.
`e Another interesting observation about this particular line, is that power levels have been cut back
`acrossall bins (From a max of 20dBm downto 11.9dBm).
`
`Cutting back on power reducesthe signal strength, which in turn reduces the SNR. The aboveline is
`very good with little noise, therefore without this cut back the above line would likely 'drown out’
`neighbouring lines at the DSLAM causing cross-talk for other lines.
`
`Note also howit can easily sync at the full 8128 kbps without having to assign the full 15 bits to any
`oneparticular tone.
`
`Top ff
`
`6/8
`
`Dish
`Exhibit 1033, Page 6
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`http://www.kitz.co.uk/adsl/adsl_technology.htm
`
`Dish
`Exhibit 1033, Page 6
`
`

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`7/2/2016
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`
`1. Kitz - ADSL Technology & DMT- Bit Allocation + Bit Swapping.::
`
`~ Bit Allocation Table and Low SNR
`
`Below is an example of a line that is more susceptible to noise.
`104
`420)
`136
`iF
`
`bi) 14 i GEG 2)
`
`hoonGe
`
`Ea)
`40
`H20
`
`2160-22 Tone
`
`e Despite having an attenuation of 30dB, the line was slightly under-performing at around 5.8
`mbps.
`Note the gaps and decline in SNR (yellow lines) at around tones 203 - 211.
`This is indicative of additional noise/interference in the frequency ranges 875kHz - 914kHz
`The decline in SNR at these frequencies has had a corresponding effect on the bit loading so that
`either side only 2 bits per bin have been able to load.
`
`Arter internal re-wiring and Cnanging TiiterS noise was reaquced on tne orrenaing Channels and tne Ine Is
`now able to syncat the full 8Mb.
`
`Top |
`
`~ Bit Allocation and Long Lines
`
`Below is a graph showing the bit loading on a long (59dB) line. Although the line is quite long it is able
`to sync at speeds up to around 2Mbps
`
` z
`
`24
`
`40
`
`56
`
`72
`
`Be
`
`14
`
`#120
`
`126
`
`«182
`
`«168
`
`6184
`
`200 62162 Tone
`
`e Long lines are naturally higher attenuated therefore SNR acrossall channels is lower.
`* Lower SNR meansless bits can be loaded per bin = lower sync speed
`¢ Notice natural tail off of SNR at the higher frequencies
`e Note where the SNR + SNR Margin at Tones 132-137 is too low to allocate any bits
`¢ A few tones at 140+ have just sufficient SNR (grey lines) to allocate 2 bits (blue lines).
`
`Whatis interesting about the above line is notice the corresponding high peak in the SNR Margin, with
`the lower bit loading at tone 74 and tone 101. This particular line had been up for a couple of days
`when the graph wasloaded. The yellow peaks indicate that that if a resync was performed 'now' then
`those bins would likely load more bits to gain a higher sync speed. This could be typical of a line that
`each evening receives a small amount of background noise' on those channels. On this particular line,
`the amountof additional bits available probably wont make that muchdifference, but the graph is a
`goodindication what to look for and showshow lines can vary over the course of the day.
`
`Top
`
`~ Seamless Rate Adaption (SRA)
`
`Seamless Rate Adaption (SRA) is a method which dynamically adapts your line rate /sync speed on the
`fly depending upon the current condition of your line without having to perform a full retrain or resync.
`
`Normally when your SNR Margin falls too low for your router to 'hear' the signal from the exchange
`your connection will drop and you lose synchronisation with the exchange. The router then has to re-
`negotiate a lower sync speed causing a small period of time without connectivity.
`
`With SRA,line conditions are constantly monitored and any increases/decreases in SNR result in an
`increase/decrease in the line connection speed without having to go through theinitialisation process.
`
`Line speed will always be at the highest possible rate depending upon your set target SNR, whichis
`particularly useful if you have had a low synchandline conditions later improve, as SRA will ensure
`that your line speed will increase in line with the better conditions.
`
`Both the router and DSLAM need to be able to support SRA.
`
`http://www.kitz.co.uk/adsl/adsl_technology.htm
`
`7/8
`
`Dish
`Exhibit 1033, Page 7
`
`Dish
`Exhibit 1033, Page 7
`
`

`

`7/2/2016
`
`1. Kitz - ADSL Technology & DMT- Bit Allocation + Bit Swapping.::
`
`Presently the only ISP in the UK that supports SRA is UKOnline on their ads] 2+ LLU exchanges.
`
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`http://www.kitz.co.uk/adsl/adsl_technology.htm
`
`8/8
`
`Dish
`Exhibit 1033, Page 8
`
`Dish
`Exhibit 1033, Page 8
`
`