ETSI TS 101 952-4 V1.1.1 (2012-12)

Access, Terminals, Transmission and Multiplexing (ATTM); Access network xDSL splitters for European deployment; Part 4: Specification for dynamic distributed filters for xDSL over POTS

DTS/ATTM-06020

General Information

• Status: Published
• Publication Date: 10-Dec-2012
• Technical Committee: ATTM TM6 - Wireline Access Network Systems
• Current Stage: 12 - Completion
• Due Date: 21-Dec-2012
• Completion Date: 11-Dec-2012

Standards Content (Sample)

Technical Specification
Access, Terminals, Transmission and Multiplexing (ATTM);
Access network xDSL splitters for European deployment;
Part 4: Specification for dynamic distributed filters
for xDSL over POTS
2 ETSI TS 101 952-4 V1.1.1 (2012-12)

Reference
DTS/ATTM-06020
Keywords
2-WIRE, access, analogue, broadband, PSTN,
splitter, xDSL
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ETSI
3 ETSI TS 101 952-4 V1.1.1 (2012-12)
Contents
Intellectual Property Rights . 5
Foreword . 5
Introduction . 6
1 Scope . 7
2 References . 7
2.1 Normative references . 7
2.2 Informative references . 8
3 Definitions, symbols and abbreviations . 9
3.1 Definitions . 9
3.2 Symbols . 10
3.3 Abbreviations . 11
4 General functional description of xDSL over POTS distributed filters . 12
4.1 Functional diagram . 12
4.2 High pass filter . 13
5 Circuit definitions, testing conditions and methods . 13
5.1 DC and ringing testing conditions . 13
5.1.1 Polarity independence . 13
5.1.2 DC feeding conditions (on-hook/off-hook) . 13
5.1.3 DC feeding and loading bridges . 14
5.1.4 Ringing signal voltage . 15
5.2 AC Terminating impedances . 15
5.2.1 Z and Z . 15
refDSL DSL
5.2.2 Z and Z , off-hook impedances . 16
R SL
5.2.3 Z , xDSL band impedance . 16
RHF
5.2.4 Z , on-hook high impedance . 16
OnHI
5.2.5 Z , on-hook low impedance . 17
OnLI
5.2.6 Z , load impedance for ringing. 17
ring
5.2.7 Z , impedance of the metering device . 17
Meter
5.3 Absence of a high pass filter . 17
5.4 General transmission test setup . 18
5.4.1 General definition of the Insertion Loss (IL) measurement . 18
5.4.2 POTS signal loss: IL between LINE port and POTS port. 18
5.4.3 xDSL signal isolation: IL between LINE and POTS ports . 20
5.4.4 xDSL signal loss . 20
5.4.5 General definition of the Return Loss . 21
5.4.6 Return Loss test set-up at LINE port and POTS port . 22
5.5 Unbalance measurement . 23
5.5.1 General definition of Longitudinal Conversion Loss . 23
5.5.2 General definition of Longitudinal Conversion Transfer Loss . 23
5.5.3 LCL and LCTL test set-up . 23
5.6 Noise measurement . 25
5.6.1 Psophometric noise in the POTS Band . 25
5.6.2 Noise in the xDSL Band . 26
6 Distributed filter requirements . 26
6.1 Option A and Option B categories . 26
6.2 DC requirements . 27
6.2.1 DC Insulation resistance between A-wire and B-wire (R ) . 27
AtoB
6.2.2 DC voltage drop (DC ) . 27
DROP
6.2.3 DC signalling . 27
6.3 Ringing frequency requirements . 28
6.3.1 Ringing voltage drop at 25 Hz and 50 Hz (V ) . 28
RD
6.3.2 Impedance at 25 Hz and 50 Hz (Z ) . 28
InRing
ETSI
4 ETSI TS 101 952-4 V1.1.1 (2012-12)
6.3.3 Total harmonic distortion at 25 Hz and 50 Hz (THD ) . 28
Ring
6.4 POTS pass band loss requirements (on-hook) . 29
6.4.1 On-hook requirement for high impedance termination (IL ) . 29
PBOnH
6.4.2 On-hook requirement for low impedance termination (IL , IL ) . 29
MaxOnH VarOnH
6.5 POTS Pass band loss requirements (off-hook) (IL , IL ). 29
MaxOffH VarOffH
6.6 POTS Passband return loss requirements (off-hook) . 30
6.6.1 Return loss requirements at the POTS port (RL ) . 30
PP
6.6.1.1 Return Loss at the POTS port for Option A . 30
6.6.1.2 Return Loss at the POTS port for Option B . 31
6.6.2 Return Loss requirements at the LINE port Option A (RL ) . 32
LP
6.6.3 Return Loss requirements at the LINE port Option B (RL ) . 32
LP
6.7 Requirements relating to metering pulses at 12 kHz or 16 kHz (IL ) (optional) . 33
Meter
6.8 Unbalance about Earth (UaE , LCL, LCTL) . 33
PB
6.9 xDSL band requirements . 34
6.9.1 xDSL band on-hook isolation between LINE and POTS port (IL ) . 34
DBOnH
6.9.2 xDSL band off-hook isolation between LINE and POTS port (IL ) . 35
DBOffH
6.9.3 Transition band signal loss: IL between POTS port and LINE port (IL ) (optional) . 35
TBOffH
6.9.4 xDSL signal loss (Att ) . 35
DB
6.10 Noise . 36
6.10.1 POTS band audible noise level requirements (N ) . 36
PB
6.10.2 xDSL band noise level (N ) . 36
DB
6.11 Distortion . 36
6.11.1 POTS band intermodulation distortion (IMD ) (optional) . 36
PB
6.11.2 DSL band intermodulation distortion (IMD ) (optional) . 37
DB
6.12 Group delay distortion . 37
6.13 Requirements related to POTS transient effects . 38
Annex A (normative): Particular requirements for dynamic distributed filters. 39
A.1 Z and Z for specific xDSL over POTS variants . 39
DSL RefDSL
A.1.1 Generic definition of Z , using Z , C and L . 39
DSL RefDSL DSL DSL
A.1.2 Z for ADSL over POTS . 40
DSL
A.1.3 Z for European VDSL1 over POTS, with US0 starting at 25 kHz . 40
DSL
A.1.4 Z for VDSL2 over POTS with US0 . 40
DSL
A.2 Common requirements for dynamic distributed filters. 41
A.3 Specific requirements for dynamic filters for ADSL or VDSL1 over POTS variants . 43
A.4 Specific requirements for dynamic filters for VDSL2 over POTS variants . 44
Annex B (informative): Bibliography . 45
History . 46

ETSI
5 ETSI TS 101 952-4 V1.1.1 (2012-12)
Intellectual Property Rights
IPRs essential or potentially essential to the present document may have been declared to ETSI. The information
pertaining to these essential IPRs, if any, is publicly available for ETSI members and non-members, and can be found
in ETSI SR 000 314: "Intellectual Property Rights (IPRs); Essential, or potentially Essential, IPRs notified to ETSI in
respect of ETSI standards", which is available from the ETSI Secretariat. Latest updates are available on the ETSI Web
server (http://ipr.etsi.org).
Pursuant to the ETSI IPR Policy, no investigation, including IPR searches, has been carried out by ETSI. No guarantee
can be given as to the existence of other IPRs not referenced in ETSI SR 000 314 (or the updates on the ETSI Web
server) which are, or may be, or may become, essential to the present document.
Foreword
This Technical Specification (TS) has been produced by ETSI Technical Committee Access, Terminals, Transmission
and Multiplexing (ATTM).
The present document is part 4 of a multi-part deliverable covering Access network xDSL splitters for European
deployment, as identified below:
Part 1: "Generic specification of xDSL over POTS splitters";
Part 2: "Generic specification of xDSL over ISDN splitters and xDSL universal splitters";
Part 3: "Generic specification of static distributed filters for xDSL over POTS";
Part 4: "Specification for dynamic distributed filters for xDSL over POTS".
NOTE 1: Useful information on splitter tests also applicable to distributed filters may be found in
TR 101 953-1-1 [i.3] and TR 101 953-2-1 [i.4]. These documents are linked to the previous versions of
the splitter specifications. [i.3] and [i.4] e.g. describe the combination of the AC testing conditions of the
test set-ups with the DC conditions controlled via feeding and loading bridges. If there is a discrepancy
between the present document and the TR 101 953 series of documents [i.3] to [i.5], the present document
prevails.
NOTE 2: The use of distributed filters is not recommended for VDSL, but it is not excluded. For this reason
TS 101 952-3 [13] and the present document refer to distributed filters for xDSL and not just for ADSL.
NOTE 3: When multiple distributed filters are installed in parallel the quality of the POTS band signals tend to
degrade proportionally to the number of filters placed at the customer's premises. To minimise this
degradation effect, especially when more than 4 filters are used, dynamic filters as specified in the present
document can be used.
The present document is fully in line with initiative "eEurope 2002 - An Information Society For All", under "The
contribution of European standardization to the eEurope Initiative, A rolling Action Plan" especially under the key
objective of a cheaper, faster and secure Internet.
ETSI
6 ETSI TS 101 952-4 V1.1.1 (2012-12)
Introduction
The present document covers all xDSL system variants, such as ADSL1, ADSL2, ADSL2plus, VDSL1 and VDSL2. It
is only applicable to the Terminal Equipment (TE) (i.e. user) side of the line. There is no equivalent of the distributed
filter at the CO side. The CO side central splitter requirements for xDSL over POTS splitters are in TS 101 952-1 [11].
The present document is coherent with TS 101 952-3 [13], specifying static distributed filters, extending the
requirements and testing methods to the dynamic filters specification.
A number of limitations and remarks of the present document should be listed:
1) The present document covers dynamic distributed filters for all xDSL technologies. However, if distributed
filters are used in VDSL2 scenarios to achieve a faster and cheaper deployment of service, operators should
realize that this could prevent VDSL to attain its maximum theoretical transmission performances, and that
ERM/EMC problems of the VDSL installation could worsen.
2) Distributed filters have less stringent isolation requirements than central splitters. The non-linearity of some
telephone sets may then cause audible back-ground noise in the POTS band, disturbing the phone conversation
and potentially even reducing the DSL capacity, particularly when the phone is picked-up.
3) Besides testing static requirements according to the present document, there is a strong need to test the
transient behaviour of dynamic filters as it may significantly affect the data transmission performances of the
associated DSL link. To this purpose, the use of TR-127 [i.11] tests of the BB forum, or of an equivalent
dynamic test methodology, is recommended as an essential complement of instrumental tests to check that the
dynamic filters do not affect the ongoing xDSL transmission. In fact, dynamic tests may prove that a filter
works correctly in a worst case xDSL test environment, including POTS DC and ringing signals.
4) The use of Option A and B for defining Return Loss is kept in the present document in exactly the same way
as it is used for POTS splitters and static distributed filters.
ETSI
7 ETSI TS 101 952-4 V1.1.1 (2012-12)
1 Scope
The present document specifies the requirements and test methods for "xDSL over POTS" dynamic distributed filters.
The distributed filters are installed at the user side of the local loop in the customer premises.
• Unlike the splitters (sometimes called central splitters to distinguish them from distributed filters) described in
TS 101 952-1 [11] and TS 101 952-2 [12], the distributed filters do not contain a high pass part. Therefore,
only the low pass part is specified and tested.
• The central splitters mentioned above are used as a single device at each end of the line while distributed
filters are normally not used as a single device but as multiple parallel devices at the user side.
2 References
References are either specific (identified by date of publication and/or edition number or version number) or
non-specific. For specific references, only the cited version applies. For non-specific references, the latest version of the
reference document (including any amendments) applies.
Referenced documents which are not found to be publicly available in the expected location might be found at
http://docbox.etsi.org/Reference.
NOTE: While any hyperlinks included in this clause were valid at the time of publication, ETSI cannot guarantee
their long term validity.
2.1 Normative references
The following referenced documents are necessary for the application of the present document.
[1] ETSI TBR 038: "Public Switched Telephone Network (PSTN); Attachment requirements for a
terminal equipment incorporating an analogue handset function capable of supporting the justified
case service when connected to the analogue interface of the PSTN in Europe".
[2] ITU-T Recommendation O.42: "Equipment to measure non-linear distortion using the 4-tone
intermodulation method".
[3] ETSI ES 203 021-3: "Access and Terminals (AT); Harmonized basic attachment requirements for
Terminals for connection to analogue interfaces of the Telephone Networks; Update of the
technical contents of TBR 021, EN 301 437, TBR 015, TBR 017; Part 3: Basic Interworking with
the Public Telephone Networks".
NOTE: ETSI TBR 021 has been made historical.
[4] ITU-T Recommendation O.41: "Psophometer for use on telephone-type circuits".
[5] ITU-T Recommendation O.9: "Measuring arrangements to assess the degree of unbalance about
earth".
[6] ETSI ES 201 970: "Access and Terminals (AT); Public Switched Telephone Network (PSTN);
Harmonized specification of physical and electrical characteristics at a 2-wire analogue presented
Network Termination Point (NTP)".
[7] ETSI EN 300 659-1: "Access and Terminals (AT); Analogue access to the Public Switched
Telephone Network (PSTN); Subscriber line protocol over the local loop for display (and related)
services; Part 1: On-hook data transmission".
[8] ETSI ES 200 778-1: "Access and Terminals (AT); Analogue access to the Public Switched
Telephone Network (PSTN); Protocol over the local loop for display and related services;
Terminal equipment requirements; Part 1: On-hook data transmission".
ETSI
8 ETSI TS 101 952-4 V1.1.1 (2012-12)
[9] ETSI ES 201 729: "Public Switched Telephone Network (PSTN); 2-wire analogue voice band
switched interfaces; Timed break recall (register recall); Specific requirements for terminals".
[10] ETSI ES 201 187: "2-wire analogue voice band interfaces; Loop Disconnect (LD) dialling specific
requirements".
[11] ETSI TS 101 952-1: "Access network xDSL splitters for European deployment; Part 1: Generic
specification of xDSL over POTS splitters".
[12] ETSI TS 101 952-2: "Access, Terminals, Transmission and Multiplexing (ATTM); Access
network xDSL splitters for European deployment; Part 2: Generic specification of xDSL over
ISDN splitters and xDSL universal splitters".
[13] ETSI TS 101 952-3: "Access, Terminals, Transmission and Multiplexing (ATTM); Access
network xDSL splitters for European deployment; Part 3: Generic specification of static
distributed filters for xDSL over POTS".
2.2 Informative references
The following referenced documents are not necessary for the application of the present document but they assist the
user with regard to a particular subject area.
[i.1] ETSI TR 102 139: "Compatibility of POTS terminal equipment with xDSL systems".
[i.2] ETSI TR 101 728: "Access and Terminals (AT); Study for the specification of low pass filter
section of POTS/ADSL splitters".
[i.3] ETSI TR 101 953-1-1: "Access and Terminals (AT); Unified and Generic Testing Methods for
European Specific DSL splitters; Part 1: ADSL splitters for European deployment; Sub-part 1:
Specification of Testing methods for Low Pass part of ADSL/POTS splitters".
[i.4] ETSI TR 101 953-2-1: "Access network xDSL transmission filters; Part 2: VDSL splitters for
European deployment; Sub-part 1: Specification of Testing methods for low pass part of
VDSL/POTS splitters".
[i.5] ETSI TR 101 953-2-3: "Access network xDSL transmission filters; Part 2: VDSL splitters for
European deployment; Sub-part 3: Specification of Testing methods for VDSL/ISDN splitters".
[i.6] ITU-T Recommendation G.992.1: "Asymmetric Digital Subscriber Line (ADSL) transceivers".
[i.7] ITU-T Recommendation G.992.3: "Asymmetric Digital Subscriber Line transceivers 2 (ADSL2)".
[i.8] ITU-T Recommendation G.992.5: "Asymmetric Digital Subscriber Line (ADSL)
transceivers - xtended bandwidth ADSL2 (ADSL2plus)".
[i.9] ITU-T Recommendation G.993.1: "Very high speed Digital Subscriber Line transceivers
(VDSL)".
[i.10] ITU-T Recommendation G.993.2: "Very high speed Digital Subscriber Line
transceivers 2 (VDSL2)".
[i.11] Broadband Forum TR-127: "Dynamic Testing of Splitters and In-Line Filters with xDSL
Transceivers", Issue 1.
ETSI
9 ETSI TS 101 952-4 V1.1.1 (2012-12)
3 Definitions, symbols and abbreviations
3.1 Definitions
For the purposes of the present document, the following terms and definitions apply:
A-wire and B-wire: wires in the 2-wire local loop connection provided from the exchange to the NTP
active splitter or active distributed filter: splitter or filter containing some active components
balun: transformer, used to convert balanced into unbalanced signals or vice-versa
central splitter: splitter that is used to isolate xDSL frequencies from POTS frequencies at a single point (often called
NTP) at the customer's premises
NOTE: It is also called a master splitter occasionally.
distributed filter: low pass filter that is added in series with each of the parallel connected POTS TE
NOTE: Each of these parallel connected filters (in the in-house cabling) is known as a distributed filter. These
filters are also known as In-line filters or microfilters.
dynamic splitter or dynamic distributed filter: splitter or filter changing its transfer behaviour dynamically,
e.g. based on the state of the POTS connection
far end echo: voiceband telephony signal that is fed back to the talker in a telephony connection with a round trip delay
(i.e. the delay between talking and hearing the feedback), of greater than 5 ms, resulting in a distinguishable echo
master splitter: See central splitter.
Network Termination Point (NTP): demarcation point between the access pair and the in-house wiring, where often
the central splitter is placed
off-hook: state of the POTS equipment at either end of a loop connection when the NTP terminal equipment is in the
steady loop state
NOTE: See ES 203 021-3 [3]. In the case where multiple TEs are present at the customer end of the loop, then the
TE is considered to be off-hook from the perspective of testing the central splitter or the distributed filter
when one terminal is off-hook.
on-hook: state of the POTS equipment at either end of a POTS loop connection when the NTP terminal equipment is in
the quiescent state
NOTE: See ES 203 021-3 [3]. In the case where multiple TEs are present at the customer end of the loop, then the
TEs is considered to be on-hook from the perspective of testing the central splitter or the distributed filter
only when all terminals are on-hook.
passive splitter or passive distributed filter: splitter or filter containing exclusively passive components
sidetone: speech that is fed back to the talker in a telephony connection with a round trip delay (i.e. the delay between
talking and hearing the feedback), of less than approximately 5 ms, making it indistinguishable from the original
utterance
static distributed filter: distributed filter not intended to change its transfer function based on the state of the POTS
connection
NOTE: These filters are also known as single state distributed filters.
static splitter: splitter not intended to change its transfer function based on the state of the POTS connection
NOTE: These splitters are also known as single state splitters.
ETSI
10 ETSI TS 101 952-4 V1.1.1 (2012-12)
3.2 Symbols
For the purposes of the present document, the following symbols apply:
Att Attenuation in the xDSL Band (LINE port to xDSL port, or reversed)
DB
C The capacitor C part of the Z
DSL DSL
DC DC voltage drop across the filter
DROP
f Highest of the used frequencies in the xDSL Band
H
f Lowest of the used frequencies in the xDSL Band
L
f Intermediate frequency, at the edge between US or US0 and the DS band for xDSL
M1
f Maximum frequency above xDSL band for measurements
Max
IL Insertion Loss xDSL Band Off-Hook
DBOffH
IL Insertion Loss (Isolation) xDSL Band On-Hook
DBOnH
IL Maximal Insertion Loss Off-Hook (in the POTS band)
MaxOffH
IL Maximal Insertion Loss On-Hook (Low Impedance, in the POTS band)
MaxOnH
IL Insertion Loss for Metering (Off-Hook)
Meter
IL Insertion Loss POTS Pass Band On-Hook
PBOnH
IL Insertion Loss Transition Band, only measured in Off-Hook
TBOffH
IL Maximal Insertion Loss Variation Off-Hook (in the POTS band)
VarOffH
IL Maximal Insertion Loss Variation On-Hook (Low Impedance, in the POTS band)
VarOnH
LCL Longitudinal Conversion Loss
LCL LCL at the LINE port
LINEport
LCL LCL at the POTS port
POTSport
LCTL Longitudinal Conversion Transfer Loss
LCTL LCTL from POTS port to LINE port
POTStoLINE
L The inductance L part of the Z
DSL DSL
N Noise in the xDSL band
DB
N Noise in the POTS band (psophometric)
PB
R DC resistance between A and B wire
AtoB
R The resistive R part of the Z (R ≡ Z )
DSL DSL DSL RefDSL
R Variable DC feed resistor in figure 3
FEED
R Variable DC load resistor in figure 4
LOAD
RL Return Loss POTS Pass Band Off-Hook
PBOffH
S Switch to connect xDSL impedance Z to the test set-up
DSL DSL
S Switch to connect N-1 filters to the test set-up, in parallel with the main filter DUT
PAR
UaE Unbalance about Earth in the POTS Band
PB
V V Ring-Drop
RD
Z Generic name for the AC POTS impedance models
AC
Z Impedance model of the input filter of a particular xDSL
DSL
Z The input impedance of the splitter or filter at the ringing frequencies
InRing
Z Generic name of the load impedance, e.g. in the figures in clause 5.4.6 on RL test set-up
LOAD
Z Generic name of the POTS ON-hook impedance
ON
Z Impedance modelling POTS On-hook with High Impedance
OnHI
Z Impedance modelling POTS On-hook with Low Impedance
OnLI
Z European harmonized complex reference POTS impedance
R
Z Generic name of Reference POTS impedance in RL formula in clause 5.4.5
Ref
Z Nominal Reference Design Impedance of xDSL (Z ≡ R )
RefDSL RefDSL DSL
Z Complex POTS impedance, extending Z to higher frequencies, see TR 102 139 [i.1]
RHF R
Z Impedance modelling the load represented by ringer circuits
Ring
Z Impedance Z Short Loop, modelling a short line terminated on 600 Ω
SL
ETSI
11 ETSI TS 101 952-4 V1.1.1 (2012-12)
3.3 Abbreviations
For the purposes of the present document, the following abbreviations apply:
AC Alternating Current
ADSL Asymmetric Digital Subscriber Line
ADSL1 Asymmetric Digital Subscriber Line 1
NOTE: ADSL limited to 1,1 MHz; specified in ITU Recommendation G.992.1 [i.6].
ADSL2 Asymmetric Digital Subscriber Line 2
NOTE: Revised in ITU-T Recommendation G.992.3 [i.7].
ADSL2plus ADSL2 "Plus"
NOTE: ADSL extended to 2,2 MHz; specified in ITU-T Recommendation G.992.5 [i.8].
CLI Calling Line Identification
CO Central Office (≡ Local Exchange ≡ LE)
CRC Cycle Redundancy Check
DC Direct Current
DS Downstream, i.e. LE to TE side
DSL Digital Subscriber Line
DTMF Dual Tone Multi-Frequency
DUT Device Under Test
e.m.f. Electro-Magnetic Force
F.F.S. For Further Study
FSK Frequency Shift Keying
HPF High Pass Filter
IL Insertion Loss
ISDN Integrated Services Digital Network
IMD Inter Modulation Distortion
ITU International Telecommunication Union
LE Local Exchange (≡ Central Office ≡ CO)
NTP Network Termination Point
POTS Plain Old Telephone Service (used throughout instead of PSTN)
PSD Power Spectral Density
PSTN Public Switched Telephone Network (replaced throughout the text by POTS)
RL Return Loss
RMS Root Mean Square
SDSL Symmetric DSL
SLIC Subscriber Line Interface Circuit
TE Terminal Equipment (e.g. Telephone, Fax, voice band modem etc.)
THD Total Harmonic Distortion
UaE Unbalance about Earth
US Upstream, i.e. TE to LE side
US0 Upstream "0" band, the lowest VDSL upstream band
NOTE: Specified in ITU-T Recommendations [i.9] and [i.10].
VDSL Very high speed Digital Subscriber Line
VDSL1 Very high speed Digital Subscriber Line 1
NOTE: Specified in ITU-T Recommendation G.993.1 [i.9].
VDSL2 Very high speed Digital Subscriber Line 2
NOTE: Specified in ITU-T Recommendation G.993.2 [i.10].
xDSL ADSL or VDSL
NOTE: This abbreviation stands for all ADSL or VDSL variants and its use this way is strictly limited to the
present group of documents; e.g. HDSL, SDSL and SHDSL are not covered.
ETSI
12 ETSI TS 101 952-4 V1.1.1 (2012-12)
4 General functional description of xDSL over POTS
distributed filters
The main purpose of the xDSL over POTS splitters is to separate or combine the transmission of POTS signals and
xDSL signals, enabling the simultaneous transmission of both services on the same twisted pair. The distributed filter
approach is implemented at the user side of the connection and, while not isolating the user plant from xDSL signals, it
nevertheless protects the POTS terminal equipment from interference due to the ingress of xDSL signals. Equally, it
also protects the xDSL transmission from transients generated primarily during POTS signalling (dialling, ringing, ring
trip, etc.) and it is also intended to prevent interference to the xDSL service due to fluctuations in impedance and
linearity that occur when telephones change their operational state (e.g. from off-hook to on-hook).
Information on various implementations of xDSL over POTS splitters and filters is given in TR 101 728 [i.2]. In
principle, the insertion of a distributed filter in existing POTS lines shall only have a low impact on the performance of
the POTS service.
The differences between a distributed filter and a central splitter (the latter being specified in TS 101 952-1 [11]) are
defined more by the location and the performance of the filter rather than by its function. Central splitters are designed
to be located at a central position, at the demarcation point of the customer premise, and provide separation of POTS
and xDSL signals at a single location. Distributed filters on the other hand are placed in series with each piece of POTS
terminal equipment (or in series with a few pieces only). Thus distributed filters are two port devices, as seen in
figure 1 (central splitters have three ports). Hence, when voice grade equipment is protected by distributed filters the
xDSL signals are delivered over the entire customer premise wiring. Multiple filters are only used at the customer's
premises, as shown in figure 1, while there is always a single central splitter at the CO side of the line.
The distributed filters are intended to be a convenient solution that can be installed by the user. The performance of both
the POTS and xDSL services is often reduced by using distributed filters instead of a central splitter. The central splitter
almost always ensures a higher input impedance for the xDSL frequency band at the line port than the distributed filters
in parallel. Moreover, in the xDSL band the central splitter isolates the in-house wiring from the external line and the
xDSL system and will almost certainly reduce electromagnetic interference.
The quality of the POTS and the xDSL services may be negatively affected by the number of distributed filters
installed. The extent of this effect is proportional to the number of distributed filters installed and also depends from
their technical characteristics. Static distributed filters [13] are classified into three categories (basic, standard,
enhanced) depending on the maximum number of devices that can be connected in parallel without degrading
unacceptably the service quality (respectively 2, 3 and 4). Dynamic distributed filters are intended to allow the parallel
operation of up to 6 devices.
4.1 Functional diagram
The functional diagram for distributed filters is given in figure 1. The filters specified by the present document are
intended to be connected only in series with the POTS TE. The serial stacking of distributed filters (i.e. connecting one
distributed filter in series with another distributed filter) is not recommended.
ETSI
13 ETSI TS 101 952-4 V1.1.1 (2012-12)
TE SIDE
FILTER
X Line
LE SIDE TE SIDE
POTS LINE
LINE POTS
SPLITTER FILTER
port port
ports ports
xDSL
POTS linecard
port
TE SIDE
at the LE or
FILTER
at a Cabinet
xDSL
POTS Terminal Equipment
port
LE- side
TE -side
Local E xchange side
xDSL transceiver at a
Ter minal E quipment side ,
i. e. at a Central Office xDSL transceiver at the
Local Exchange or
customer premises
Remote xDSL Terminal i .e. at Customer Premises
or a Cabinet
NOTE: For a Local Exchange xDSL deployment, the length "X" in this figure will typically be far less than 1 km.
For a remote xDSL terminal deployment, the length "X" can be up to several kilometres.

Figure 1: Functional diagram of the DSL splitter configuration with distributed filters
4.2 High pass filter
The transfer function between the POTS port and LINE port (and vice-versa) of each TE side filter in figure 1 is that of
a low pass filter, as shown in figure 2. The LINE and the xDSL ports coincide for a distributed filter, i.e. there is no
optional highpass as is allowed for POTS central splitters, or no mandatory DC blocking capacitors, as is the case for
ISDN splitters, or universal splitters, as explained in TS 101 952-1 [11] and TS 101 952-2 [12]. For distributed filters
the xDSL transceiver contains the DC blocking function and an additional high pass functionality.

Figure 2: Structure of the xDSL distributed filter
5 Circuit definitions, testing conditions and methods
5.1 DC and ringing testing conditions
5.1.1 Polarity independence
The distributed filter shall conform to all the applicable requirements of the present document for both polarities of the
DC line feeding voltage.
5.1.2 DC feeding conditions (on-hook/off-hook)
The electrical requirements in the present document can be classified as follows (see also under definitions):
• On-hook requirements, when all POTS terminals are in the on-hook state.
• Off-hook requirements, when at least one POTS terminal is in the off-hook state.
• Transitional requirements, when one POTS terminal is in the transition from the on-hook to the off-hook state
or vice versa.
ETSI
14 ETSI TS 101 952-4 V1.1.1 (2012-12)
On-hook voice band electrical requirements shall be met with a DC feeding voltage of 24 V to 30 V, and using the
(voice band) impedance model Z , in a high impedance Z and low impedance Z variant as given in
ON OnHI OnLI
clauses 5.2.4 and 5.2.5 of the present document.
On-hook requirements are tested with a DC load of several MΩ and a negligible current. For high impedance IL tests
the DC loading bridge shall not be used to interface the filter output with the load.
However, it should be noted that in certain networks there may be on-hook signalling requiring a DC loop current in the
range of 0,4 mA to 2,5 mA flowing through the distributed filter. In this case the AC impedance model Z is used to
OnLI
terminate the LINE and POTS port of the distributed filter at voice frequencies and the loading bridge shall be used
and the R be tuned to achieve the desired DC current.
LOAD
NOTE: It is recognized that, in some networks, DC feeding currents in steady state up to 100 mA or higher can
occur. Similarly there are networks in which the maximum DC feeding current is limited, e.g. by the
SLIC. This might allow filter designs to be adapted to these specific conditions.
5.1.3 DC feeding and loading bridges
To inject a DC voltage and control the DC current separately from the AC impedances, a feeding circuit is used at the
LE side and a loading (or holding) circuit is used at the TE side. These circuits, which are called bridges throughout this
text, have an equivalent electrical circuit as shown in the figures 3 and 4. For balance C1 ≡ C2 and L1 ≡ L2.
Feeding Bridge
C1
Connected to
AC the LINE port
Z
C2
AC
port of the distributed
filter(s)
Voiceband signals and
(TE side)
L1 L2
impedances connected
at the AC port
DC port
V (tunable)
DC
R /2 (tunable) R / 2 (tunable)
FEED FEED
Figure 3: Feeding Bridge (connected to the LINE port of the distributed filter)

Loading Bridge
C1
Connected to
the POTS port AC
Z
AC
C2
of the distributed
port
filter (TE side)
Voiceband signals and
L2
L1
impedances connected
DC port
at the AC port
R
LOAD(tunable)
hook simulator
Figure 4: Loading Bridge (connected to the POTS port of the distributed filter)
The V (battery) voltage of the feeding bridge is tunable to achieve the required feeding conditions for each test.
DC
However its value shall be:
• V = 24 V to 30 V
DC
ETSI
15 ETSI TS 101 952-4 V1.1.1 (2012-12)
NOTE 1: This low voltage value is intended to assure that dynamic filters using the open circuit DC voltage as a
threshold criterium for assessing the POTS line state make the correct assumptions also in case of low
voltage feeding bridges, as still used in some networks.
Also R and R resistors are tunable for achieving the required feeding conditions for each test. The following
FEED LOAD
rules apply:
• For off-hook tests: R ≤ 150 Ω
LOAD
• For on-hook tests with low impedance termination the required DC current shall be obtained by increasing
R , without decreasing V or increasing R , with respect to their values set for executing the off-hook
LOAD DC FEED
tests
The properties of the feeding and loading bridges should be sufficiently good, to prevent that measurements of
distributed filter properties are affected by these bridges. In particular the following requirements apply to the direct
cascaded connection of the feeding bridge with the loading bridge, as measured between the AC ports of the feeding
bridge and of the loading bridge, to be verified for all the DC current conditions used in the filter tests.
Insertion loss (see clause 5.4.1, Z = Z = Z ): ≤ 0,1 dB (300 Hz to 4 k
...