1、 TECHNICAL REPORT ATIS-0600027 Guidance for the Use of Upstream Power Back Off Parameters for ITU-T Recommendation G.933.2 Annex A, Issue 2 ATIS is the leading technical planning and standards development organization committed to the rapid development of global, market-driven standards for the info
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5、 American National Standards Institute (ANSI). For more information, please visit . Notice of Disclaimer therefore this TR provides guidance in the following areas: Explanation of the technical meaning of these two parameters. Examples of the use of UPBO parameters a and b in a North American enviro
6、nment. Guidance on the configuration of these two parameters in North American implementations of VDSL2. Although this TR provides information on the configuration of these parameters, the guidance is of an explanatory nature. Specifically this Technical Report is not an ATIS Standard and values in
7、examples and the guidance in this Technical Report are not requirements for either default values or the field configuration for parameters a and b . The examples in this TR do not necessarily result in optimum values for either of these parameters in specific field situations and obtaining such opt
8、imum configuration for UPBO operation of VDSL2 may require field implementation specific information that is outside the scope of this TR. Issue 2 of this TR adds a discussion the UPBO a and b parameters for the US-3 band as utilized by the 30a VDSL2 profile. 1.2 Purpose This TR provides technical g
9、uidance to the Industry, that is network operators, and vendors of VDSL2 equipment and operations support software, on the meaning and usage of the VDSL2 UPBO a and b parameters for North American field implementations of VDSL2. Its purpose is to provide information on the technical meaning and guid
10、ance on the configuration of these two parameters. ATIS-0600027 2 1.3 Application This TR provides guidance to network operators and vendors on the proper usage of the G.993.2 UPBO parameters a and b . 2 References The following standards contain provisions, which through reference in this text cons
11、titute a basis of technical discussion in this ATIS Technical Report. At the time of publication, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this ATIS Technical Report are encouraged to investigate the possibility of applying the most
12、 recent editions of the standards indicated below: 1 G.993.2, Very High Speed Digital Subscriber Line Transceivers 2 (VDSL2), ITU-T, Geneva, February 2006, including Amendment 1, July 2007 and Amendment 2, February 2008.12 G.993.1 Very High Speed Digital Subscriber Line Transceivers, ITU-T, Geneva,
13、June 2004.13 ATIS-0600424.2004(R2009), - Interface Between Networks and Customer Installation, Very High Speed Digital Subscriber Line (VDSL) Metallic Interface (DMT Based),2. 4 G.997.1 Physical layer management for digital subscriber line (DSL) transceivers, ITU-T, Geneva, June 2006 including Amend
14、ment 1, December 2006 and Amendment 2, November 2006.13 Definitions, Acronyms, & Abbreviations 3.1 Definitions 3.1.1 Reference Length: The Reference Length (RL) for Upstream Power Back Off is the electrical length of a loop for which no Upstream Power Back Off will occur if the actual electrical len
15、gth of a particular loop is greater than the Reference Length. 3.1.2 Upstream Power Back Off: Upstream Power Back Off is the method defined in ITU-T Recommendations G.993.1 2 and G.993.2 1 for reducing the transmitted power in the upstream direction on shorter loops to reduce crosstalk into longer l
16、oops that are also transporting VDSL2 in the same cable/binder. 1This document is available from the International Telecommunications Union. 2This document is available from the Alliance for Telecommunications Industry Solutions, 1200 G Street N.W., Suite 500, Washington, DC 20005. ATIS-0600027 3 3.
17、2 Acronyms & Abbreviations ATIS Alliance for Telecommunications Industry Solutions AWG American Wire Gauge FEXT Far End Crosstalk ITU-T International Telecommunications Union Telecommunications Standards Sector PSD Power Spectral Density RL Reference Length TR Technical Report UPBO Upstream Power Ba
18、ck-Off VDSL2 Very High Speed Digital Subscriber Line 2 US0 The Upstream 0 band of the VDSL2 Recommendation US1 The Upstream 1 band of the VDSL2 Recommendation US2 The Upstream 2 band of the VDSL2 Recommendation US3 The Upstream 3 band of the VDSL2 Recommendations 4 Upstream Power Back Off Configurat
19、ion This Technical Report (TR) provides guidance on the configuration of the a and b values for UPBO for VDSL2 in North America. This TR provides guidance to the Industry in the following areas: Section 4.1 discusses the meaning of the UPBO parameters a and b for VDSL2 and the context in which they
20、are used by a North American Operator. As the values of a and b can be used to optimize UPBO with respect to the specifics of a Network Operators plant in particular locations, the TR provides guidance as to the meaning of the parameters and the general effects of changes in their values. However, s
21、pecific techniques for optimizing the values are not in the scope of this TR. Section 4.2 provides a discussion on optimum values for a and b . Section 4.3 Provides examples of the use of a and b on sample loops of various gauges. This TR emphasizes that in North America the values for a and b be co
22、nfigurable by the Network Operator, as is currently required in the ITU-T Recommendations, to enable optimization of UPBO. Note: The analysis that follows assumes the limit mask is flat for each upstream band, i.e. beyond the reference length used for an upstream band Ui, the PSD level will nominall
23、y be aiacross the entire band. ATIS-0600027 4 4.1 What are the UPBO a and b parameters In G.993.2 1 the PSD Mask for Upstream Power Back Off (UPBO), UPBOMASK, is defined in Section 7.2.1.3.2 of that recommendation by formulas which define the UPBOMASK as functions of f , frequency, in MHz, kl0, elec
24、trical length of the loop as defined in G.997.1 2, and two variables a and b . In the equations defining UPBOMASK in Section 7.2.1.3.2 of G.993.2 the term abf defines a reference PSD based on an assumed nominal transmit PSD and the loss on an assumed Reference Loop of a particular Reference Length.
25、The reference lengths assumed for the US1, US2 and US3 bands for a given network deployment will often, but not always, be different lengths for the respective upstream bands. The formulas that define UPBOMASK use a to set an assumed nominal transmit PSD and b to model a loop that corresponds to the
26、 Reference Length (RL) where the loss on the reference loop is modeled as being proportional to f such that bf approximates the loss of a loop of length RL. When a is set to the nominal transmit PSD3for a particular band the effect of the term abf on the formula for UPBOMASK is that no upstream powe
27、r back off is applied for loops whose electrical length, kl0, is greater than the RL that is determined by the setting ofb . ITU-T Recommendation G.997.1 4 defines the parameter UPBOPSD-pb to allow the Network Operator to configure a and b for each upstream band except US0.4Figure 1 illustrates the
28、relationship between various settings of b and reference lengths of 26 AWG loops at 1000ft, 1500ft, 2000ft, 2500ft5and 3000ft and insertion loss modeled across the VDSL2 US1 band6. In general the set of values a and bfor each upstream band are set to same values for all loops in a binder. As mention
29、ed above a is typically set to the Transmit Template PSD, which for the VDSL2 US1, US2, and US3 bands is the Limit PSD Mask 3.5dB. The value of a is configurable to allow the Network Operator to tune the behavior of UPBO when a PSD Mask is set in the upstream direction that modifies the Transmit Tem
30、plate PSD for a modem to one below the Transmit Template PSD. 3The default nominal transmit PSD in VDSL2 is (LimitMask for the band 3.5) dB. This PSD is flat for US Bands in Annex A of VDSL2.) 4As the formula abf has units of dBm / Hz in the definitions of a and b in the ITU-T Recommendations and in
31、 the guidance provided in this TR the values of a are in units of dBm / Hz and of b are in units of dB / Hz . 5It can be shown that the b value specified for the US1 band in T1.424 3 for the F noise model and the M2 template equates to a US1 RL of 2621 ft. A US2 RL of approximate 1700 ft provides ro
32、ughly the same attenuation across the US2 band. 6Section 4.3 provides examples of a and b settings for the US1, US2 and US3 bands for both 26 AWG and 24 AWG loops. ATIS-0600027 5 Figure 1 -Various Reference Lengths and Best Fit Values of b in the US 1 Band ,Increasing the reference length (RL), that
33、 is increasing b , in the UPBO formulas results in lowered upstream FEXT from shorter loops into the longer loops. However the reduced power also leads to reducing the maximum upstream bit rate available on the short loops to a rate at least equal to that which would be possible if the short loop le
34、ngth were equal in the length RL. Increasing the value of b thus reduces the upstream bandwidth achievable on all the loops shorter than the RL. 4.2 Issues on the Optimization of UPBO Determining the optimum setting of b for any particular implementation of VDSL2 involves evaluating the above trade
35、off in terms of both particular characteristics of the Network Operators loop plant and their specific VDSL2 customer service models and requirements. Because of this, determining optimum values of b (reference lengths) for the VDSL2 upstream bands is likely to be dependent on conditions specific to
36、 particular Network Operators environments, possibly varying among different metropolitan areas or even in some cases from access node to access node. It must be assumed if UPBO is to be configured in a North American field implementation that equipment supporting VDSL2 is compliant with the ITU-T R
37、ecommendations G.997.1 and G.993.2 with respect to the ability to set the values of a and b . That is the values of a and b must be configurable by the Network Operator if they are to utilize UPBO. ATIS-0600027 6 4.3 Examples of the a and b Settings for North American Loops The following tables prov
38、ide a list of b values and the corresponding Reference Length (RL) for example 26 AWG and 24 AWG loops in the US1, US2 and US3 VDSL2 bands. In all these tables a is set to a value of the Transmit Template PSD as defined in G.993.2 section 7.2.1 and Annex A1 which for the VDSL2 US1, US2 and US3 bands
39、 is the Limit PSD Mask 3.5dB. That is, US1 band: a 53dBm / Hz US2 band: a 54dBm / Hz US3 band: a=60dBm / Hz The examples in these tables provide guidance as to acceptable initial values for b in North America for the example loops listed below. However, as discussed in section 4.2, they are not nece
40、ssarily optimal values for any particular field implementation of VDSL2 and are not recommended default values for b in North America. Guidance for the US0 band is for further study.Table 1 - b vs Reference Length (RL) for 26 AWG Loops in the US1 Band Value of b in dB / Hz Reference Length (RL) in f
41、eet 24.25 3000 20.21 2500 16.17 2000 12.13 1500 8.08 1000 6.06 750 4.04 500 2.02 250 ATIS-0600027 7 Table 2- b vs Reference Length (RL) for 26 AWG Loops in the US2 Band Value of b in dB / Hz Reference Length (RL) in feet 20.57 2500 16.45 2000 12.34 1500 8.23 1000 6.17 750 4.11 500 2.06 250 Table 3-
42、b vs Reference Length (RL) for 26 AWG Loops in the US3 band Value of b in dB/ Hz Reference Length (RL) in feet 8.33 1000 6.25 750 4.17 500 2.08 250 ATIS-0600027 8 Table 4- b vs Reference Length (RL) for 24 AWG Loops in the US1 Band Value of b in dB / Hz Reference Length (RL) in feet 22.52 3500 19.30
43、 3000 16.09 2500 12.87 2000 9.65 1500 6.43 1000 4.82 750 3.22 500 1.61 Note: An implementation that estimates the electrical length kl0to be less than 1.8 for this loop and subsequently uses a value of 1.8 (per 7.2.1.3.2 of G.993.2) will result in UPBO effectively being disabled. 250 Table 5- b vs R
44、eference Length (RL) for 24 AWG Loops in the US2 Band Value of b in dB / Hz Reference Length (RL) in feet 22.76 3500 19.51 3000 16.26 2500 13.01 2000 9.76 1500 6.50 1000 4.88 750 3.25 500 1.63 - Note: An implementation that estimates the electrical length kl0to be less than 1.8 for this loop and sub
45、sequently uses a value of 1.8 (per 7.2.1.3.2 of G.993.2) will result in UPBO effectively being disabled. 250 ATIS-0600027 9 Table 6- b vs Reference Length (RL) for 24 AWG Loops in the US3 band Value of b in dB/ Hz Reference Length (RL) in feet 6.58 1000 4.94 750 3.29 500 1.65 - Note: An implementation that estimates the electrical length kl0to be less than 1.8 for this loop and subsequently uses a value of 1.8 (per 7.2.1.3.2 of G.993.2) will result in UPBO effectively being disabled. 250
