WIXLIB

DQS: DSL Quality Management Techniques and NomenclatureTR-197 Issue 2[13] TR-176ADSL2Plus Configuration Parameters for IPTVBBF2008[14] TR-188DSL Quality SuiteBBF2010[15] TR-198DQS: DQM systems functional architecture andrequirementsBBF2010[16] TR-202ADSL2/ADSL2plus Low-Power Mode GuidelinesBBF2010[17] MR-204Energy Efficiency, Dematerialization and the Roleof the Broadband ForumBBF2009[18] Deliverable Position paper on Dynamic SpectrumTF2.2Management (DSM) and Dynamic Line-CodeManagement (DLCM)IST-MUSEproject2005[19] Deliverable Static and Dynamic Spectral ManagementB2.1Analysis - Issue 2IST-MUSEproject2006[20] Deliverable Migration guidelines for DSL from operator’sB2.3viewIST-MUSEproject2005[21] ATIS-PP0600007Dynamic Spectrum ManagementATISCOAST2007[22] NICC ND1513Report on Dynamic Spectrum Management (DSM) NICCMethods in the UK Access Network2010[23] ANSIT1.417Spectrum Management For Loop TransmissionSystems, American National Standard ForTelecommunicationsANSI2003[24] NICC ND1602Specification of the Access Network FrequencyPlan applicable to transmission systemsconnected to the BT Access NetworkNICC2011[25] ATIS0600027Guidance for the Use of Upstream Power BackOff Parameters for ITU-T RecommendationG.993.2 Annex A, Issue 2ATISCOAST20102.3AbbreviationsThis Technical Report uses the following abbreviations:ADSLAMANCOCPEDELTDLCMAsymmetric Digital Subscriber LineAmplitude ModulationAccess NodeCentral OfficeCustomer Premises EquipmentDual Ended Line TestDynamic Line Code ManagementDecember 2014 The Broadband Forum. All rights reservedPage 9 of 76

DQS: DSL Quality Management Techniques and NRFISDTVSELTSHDSLSHINESNRSNRMSRASSMTR-197 Issue 2Dynamic Line ManagementDiscrete Multi-ToneDSL Quality ManagementDSL Quality SuiteDigital Subscriber LineDynamic Spectrum ManagementFrequency Division MultiplexingForward Error CorrectionFar End CrosstalkAmateur radioHigh bit rate Digital Subscriber LineHigh Definition TelevisionInter Arrival TimeImpulse Noise ProtectionImpulse Noise Protection EquivalentInternet Protocol TelevisionLoss Of MarginLong waveMetallic Line TestMedium waveNear End CrosstalkOperations Support SystemProlonged Electrical Impulse NoisePower Spectral DensityQuality of ExperienceQuality of ServiceRepetitive Electrical Impulse NoiseRadio Frequency InterferenceStandard Definition TelevisionSingle Ended Line TestSymmetric High-speed Digital Subscriber LineSingle High-level Impulse NoiseSignal-to-Noise RatioSignal-to-Noise Ratio MarginSeamless Rate AdaptationStatic Spectrum ManagementDecember 2014 The Broadband Forum. All rights reservedPage 10 of 76

DQS: DSL Quality Management Techniques and NomenclatureSWTDDTDMAVDSLVNTR-197 Issue 2Short waveTime Division DuplexingTime Division Multiple AccessVery high-rate Digital Subscriber LineVirtual NoiseDecember 2014 The Broadband Forum. All rights reservedPage 11 of 76

DQS: DSL Quality Management Techniques and Nomenclature3TR-197 Issue 2Technical Report Impact3.1Energy EfficiencyThe scope of TR-197 covers improvements in energy efficiency.3.2IPV6TR-197 has no impact on IPv6.3.3SecurityTR-197 has no impact on security.3.4PrivacyTR-197 has no impact on privacy.December 2014 The Broadband Forum. All rights reservedPage 12 of 76

DQS: DSL Quality Management Techniques and Nomenclature4TR-197 Issue 2IntroductionDSL Quality Management (DQM), per its definition in TR-188 “DSL Quality Suite” [14], aimsto improve the stability, quality and performance of DSL lines. An additional benefit withrespect to these objectives is the ability to improve energy efficiency. Generally speaking, this isachieved by means of “DSL line management techniques” that will be referred to as DQMtechniques in the remainder of this document. A DQM technique modifies (groups of)parameters to achieve certain effects on the line.The essence of a DQM technique is its method, i.e. the concatenation of processes“data collection – analysis/diagnosis – changes on the line(s)” to achieve the goal(s) of thetechnique (e.g. stability increase, quality improvement, service/performance upgrade, etc.).Hence, implicitly a DQM technique is associated with monitoring the line itself and - dependingon each case - it is typically focused on specific parameters associated to the nature of thetechnique.Typically DQM technique categories focus on a given stability/performance “area” of DSLtransmission strictly influenced by a group of parameters configured in the line profile. In otherwords the usual objective of finding the appropriate trade-off between reducing noise influenceand maintaining good bitrates leads to the “tuning” of the DSL line code or the signal spectrum.This introduces two main categories of DQM techniques: Dynamic Line Code Management(DLCM) and Dynamic Spectrum Management (DSM). New transceiver functionalities such asVirtual Noise and Retransmission may be exploited to build up new techniques and in certaincases the combined use of basic techniques leads to structured ones that better fit troublesomeline conditions experienced in real networks. Furthermore line testing techniques such as SELT,DELT and MELT can be utilized to further enhance troubleshooting capabilities and they canalso be used to trigger other DQM methods.Enhancing the energy efficiency of DSL broadband access networks has become increasinglyimportant as part of the emerging trend towards green Information and CommunicationTechnology (ICT). DQM techniques may help improve energy efficiency. Many DSL linestransmit excessive power and are often underutilized. There is a fundamental trade-off betweenperformance, stability, and energy usage. In general, improving one of these three axes meansthat at least one of the others may degrades, although this degradation could be imperceptible insome cases. A DQM system can manage multiple DSL lines to manage the trade-offs betweenthese parameters. Reducing power appropriately on a given line may not decrease the data rate orline stability (depending on the service rate and performance specification) of that line, and itmay sometimes even result in increased data rates or stability for neighbouring lines due tocrosstalk reduction.This Technical Report develops a categorization and description of the building blocks of DQMtechniques and provides guidance for their use in a stand-alone or combined manner. This isdone coherently with the architectural specification of DQM systems provided in TR-198 [15].This Technical Report provides a taxonomy of DQM techniques. It is solely informative andcontains no normative requirements or recommendations regarding the advisability of use of anyDecember 2014 The Broadband Forum. All rights reservedPage 13 of 76

DQS: DSL Quality Management Techniques and NomenclatureTR-197 Issue 2particular technique. Furthermore, specification of the design, implementation or performancecapabilities of any DQM algorithm or technique is outside the scope of this Technical Report.December 2014 The Broadband Forum. All rights reservedPage 14 of 76

DQS: DSL Quality Management Techniques and Nomenclature5TR-197 Issue 2DSL Quality Impairments and Indicators5.1Crosstalk NoiseCrosstalk is one of the major limiting factors on the performance of DSL systems if propermanagement and/or mitigation techniques are not used. It occurs when the electromagneticcoupling between different transmission lines causes interference between the signals. In simplewords this means that the signal from one line is “leaking” into a second line where it is seen asnoise and thus decreases the SNR of the transmission on that line.Twisted pairs are typically grouped into cable binders. Within a binder the lines are located veryclose to each other and the closer they are the higher the coupling and thus the crosstalk will be.The effect of crosstalk can however be decreased by using different twist lengths on differentpairs to reduce the symmetry and thereby reducing the coupling between them. Different binderscan also be twisted around each other so that no two binders are adjacent for long runs, tominimize the crosstalk. The twisting is however not perfectly random and a line is typicallyadjacent to some of the lines in the cable for longer distances than to some other lines in thesame cable. Also, the conductors are not perfectly identical and so there is at least some smallcapacitive unbalance between pairs. This means that typically one line in a cable may experiencemore crosstalk than other lines in the same cable. The level of crosstalk is hence highlydependent on the type and quality of the cable and it will vary from pair to pair and withfrequency.There are two different types of crosstalk, Near End crosstalk (NEXT) and Far End crosstalk(FEXT). NEXT is the crosstalk from a transmitter to a receiver that is located in the same end ofa transmission line. This can cause a severe impairment since the signal sent from the remotetransmitter has been attenuated along the transmission line before reaching the local receiverwhile the leaking signal just was sent out from another local transmitter and thus has not beenattenuated as much. FEXT is the crosstalk leaking into another transceiver on the opposite end ofthe subscriber loop. This means that the induced crosstalk has to travel along the line and boththe signal and the crosstalk will be attenuated by the loop. The different paths of the NEXT andthe FEXT crosstalk are shown in Figure 1.December 2014 The Broadband Forum. All rights reservedPage 15 of 76

DQS: DSL Quality Management Techniques and NomenclatureTR-197 Issue 2FEXT is shown in blue and NEXT in redCO TransmitterSystem1CPE ReceiverSystem 1CO ReceiverSystem 1CPE TransmitterSystem 1CO TransmitterSystem2CPE ReceiverSystem 2CO ReceiverSystem 2CPE TransmitterSystem 2Figure 1: The different paths of crosstalkIn some deployment scenarios the twisted pairs inside a cable binder are used for different typesof DSL services. The crosstalk disturber can therefore originate from transmission lines runningany kind of DSL service e.g. HDSL, SHDSL, ADSL or VDSL. The crosstalk that originatesfrom a signal of the same service as the disturbed signal is often referred to as self crosstalkwhile crosstalk between different types of services are called foreign or alien crosstalk. SelfNEXT can be avoided by using a frequency division multiplexed (FDM) system where differentfrequency bands are used for upstream and downstream tones. By avoiding overlappingfrequency bands there is no NEXT in the receive bands and thus no impact on SNR. Thistechnique is for example commonly used in ADSL/ADSL2/ADSL2plus and VDSL2. This wayof avoiding NEXT is however not possible for alien crosstalk since different kinds of servicesuses different bandwidth and the spectra of many types of services overlap.5.1.1 Stationary CrosstalkIf the transmission system conditions for a line are constant and the number of disturbers isfixed, then the crosstalk seen by that line will also stay constant. This is called stationarycrosstalk. Stationary crosstalk will decrease the SNR and thus the performance of DSL if it is notmitigated properly. It will then also limit the reach of a service requiring a specific bit rate.However, stationary crosstalk does not decrease the DSL stability.5.1.2 Short-Term Stationary CrosstalkSome types of DSL transmitters operate in transmission modes in which an “ON” condition (inwhich the transmitter generates a signal) alternates with an “OFF” condition (in which thetransmitter is silent or generates only a pilot tone). Examples of such transmitters include TDDor TDMA systems, and burst transmission systems that use quiescent modes

Broadband Forum Technical Reports in the DSL Quality Suite, TR-197 describes the published techniques and DSL capabilities and introduces the nomenclature used. Issue 2 of TR-197 includes new material on the use and impact of energy saving techniques in the context of DQM.