ETSI TS 101 548 V1.1.1 (2014-09)

Access, Terminals, Transmission and Multiplexing (ATTM); European Requirements for Reverse Powering of Remote Access Equipment

DTS/ATTM-06100-1

General Information

• Status: Published
• Publication Date: 01-Sep-2014
• Technical Committee: ATTM TM6 - Wireline Access Network Systems
• Current Stage: 12 - Completion
• Due Date: 15-Dec-2014
• Completion Date: 02-Sep-2014

Standards Content (Sample)

TECHNICAL SPECIFICATION
Access, Terminals, Transmission and Multiplexing (ATTM);
European Requirements for Reverse Powering
of Remote Access Equipment
2 ETSI TS 101 548 V1.1.1 (2014-09)

Reference
DTS/ATTM-06100-1
Keywords
VDSL2
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3 ETSI TS 101 548 V1.1.1 (2014-09)
Contents
Intellectual Property Rights . 4
Foreword . 4
Modal verbs terminology . 4
Introduction . 4
1 Scope . 5
2 References . 5
2.1 Normative references . 5
2.2 Informative references . 5
3 Definitions, symbols and abbreviations . 6
3.1 Definitions . 6
3.2 Symbols . 6
3.3 Abbreviations . 6
4 Introduction to Reverse Power Feed . 8
4.1 Introduction . 8
5 Reverse Power Feed Architecture . 9
5.1 Introduction . 9
5.2 Reverse Power Feed and POTS Co-Existence . 9
5.2.1 Background . 9
5.2.2 POTS Adapters . 10
5.2.2.1 POTS Adapter - E (POTSA-E) . 10
5.2.2.2 POTS Adapter - C (POTSA-C) . 10
5.2.2.3 POTS Adapter - D (POTSA-D) . 10
5.3 Reverse Power Feed Architecture without POTS on the same pair (RPFA-NOP). 11
5.4 Reverse Power Feed Architecture with Baseband POTS from the Exchange (RPFA-EXP). 12
5.5 Reverse Power Feed Architecture with Baseband POTS from the Exchange Sharing the in-premises
Wiring (RPFA-EXPSW) . 14
5.6 Reverse Power Feed Architecture with Derived POTS (RPFA-DRP) . 15
5.7 Reverse Power Feed Architecture with Derived POTS Sharing the in-premises Wiring (RPFA-DRPSW) . 16
6 Reverse Power Feed Start-Up Protocol . 17
6.1 Introduction . 17
6.2 Communications-based Start-up (CBSU) Protocol . 18
6.3 CBSU Protocol Specific Transmission Parameters . 20
7 Reverse Power Feed Power Supply Characteristics . 21
7.1 RPF Range Options and Classes . 21
7.2 RPF Safety Requirements . 24
7.2.1 Background . 24
7.2.2 Unintended consequences . 25
7.3 Electrical reference model . 25
7.4 Zero touch DPU . 26
Annex A (informative): Reverse power backup systems . 27
A.1 Case 1 battery backup in the CPE . 27
A.2 Case 2 battery backup in the DPU and CPE . 27
Annex B (normative): General POTS requirements . 28
Annex C (informative): Bibliography . 29
History . 30

ETSI
4 ETSI TS 101 548 V1.1.1 (2014-09)
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).
Modal verbs terminology
In the present document "shall", "shall not", "should", "should not", "may", "may not", "need", "need not", "will",
"will not", "can" and "cannot" are to be interpreted as described in clause 3.2 of the ETSI Drafting Rules (Verbal forms
for the expression of provisions).
"must" and "must not" are NOT allowed in ETSI deliverables except when used in direct citation.
Introduction
As various Operators consider the deployment of fibre-fed remote nodes that contain xDSL DSLAM equipment, it is
necessary to consider the means of powering such remotely located equipment. One such method, known as "reverse
power feed", transmits the power from the customer premises to the fibre-fed remote node using the distribution-side
copper network. The present document defines a reverse power feed transmission standard which allows Operators to
source suitably compliant equipment for inclusion in their networks. The reverse power feed methodology can be used
to power a remote node hosting any metallic transmission system (e.g. FAST [i.6], VDSL2 [i.7], etc.).
ETSI
5 ETSI TS 101 548 V1.1.1 (2014-09)
1 Scope
The present document defines architectures for reverse powering of remote network nodes from multiple CPEs. The
architectures describe how to combine reverse power feed with POTS and data transmission. Options for combining
reverse powering with battery backup are also described. The present document identifies requirements for POTS
signalling translation when operated over reverse power feed. Start-up protocols are defined that will ensure safe
connection of reverse powered systems. Management requirements for reverse power feed and power combining within
the remote network node are specified.
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 ES 202 971: "Access and Terminals (AT); Public Switched Telephone Network (PSTN);
Harmonized specification of physical and electrical characteristics of a 2-wire analogue interface
for short line interface".
[2] CENELEC EN 60950-1: "Information Technology Equipment - Safety Part 1: General
requirements (IEC 60950-1:2005 + Cor.:2006 + A1:2009, modified)".
[3] ETSI ES 203 021: "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".
[4] Recommendation ITU-T G.994.1: "Handshake procedures for digital subscriber line transceivers".
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] IEEE 802.3: "LAN/MAN CSMA/CD (Ethernet) Access Method".
NOTE: Available at http://standards.ieee.org/getieee802/802.3.html.
[i.2] NICC ND 1645 (V1.1.2) (2011-06): "NGA Telephony; Architecture and requirements".
NOTE: Available at http://www.niccstandards.org.uk/files/current/ND1645v1.1.2.pdf?type=pdf.
[i.3] ETSI TS 101 952-1: "Access network xDSL splitters for European deployment; Part 1: generic
specification of xDSL over POTS splitters".
[i.4] Recommendation ITU-T G.993.2: "Very high speed digital subscriber line transceivers 2
(VDSL2)".
[i.5] Recommendation ITU-T G.993.2 Amendment 5: "Short reach VDSL2 with reduced power and
enhanced data rate".
ETSI
6 ETSI TS 101 548 V1.1.1 (2014-09)
[i.6] Recommendation ITU-T G.9700 (04/14): "Fast access to subscriber terminals (FAST) - Power
spectral density specification".
[i.7] ETSI TS 101 271 (V1.2.1): "Access, Terminals, Transmission and Multiplexing (ATTM);Access
transmission systems on metallic access cables; Very High Speed digital subscriber line system
(VDSL2) [Recommendation ITU-T G.993.2 modified]".
3 Definitions, symbols and abbreviations
3.1 Definitions
For the purposes of the present document, the following terms and definitions apply:
power splitter: device that performs a frequency splitting/combining function between the services being carried
(which can include POTS and xDSL based services) and the injected DC electrical power
service splitter: low pass filter that separates baseband POTS from xDSL frequencies
NOTE: The relevant specifications for the service splitter can be found in ETSI TS 101 952-1 [i.3].
3.2 Symbols
For the purposes of the present document, the following symbols apply:
R 2-wire analogue presented interface
U-R Reference point at CPE containing both DC power and service data
U-R2 Reference point at CPE containing the filtered service data
U-R2P Reference point at CPE containing the injected DC power
U-R2S Reference point at CPE containing the baseband POTS and the converted POTS signalling
U-O Reference point at DPU containing both DC power and service data
U-O2 Reference point at DPU containing the filtered service data
U-O2O Reference point at DPU containing the baseband POTS and the converted POTS signalling
U-O2P Reference point at DPU containing the extracted DC power
3.3 Abbreviations
For the purposes of the present document, the following abbreviations apply:
4PPoE 4-Pair Power over Ethernet
ACT Active
ATA Analogue Telephone Adapter
BAT Battery
CBSU Communications based Start-Up protocol
CO Central Office
CP Customer Premises
CPE Customer Premises Equipment
CPE ME CPE's Management Entity
DBPSK Differential Binary Phase Shift Keying
DC Direct Current
DN Distribution Network
DP Distribution Point
DPU Distribution Point Unit
DPU ME DPU's Management Entity
DSL Digital Subscriber Line
FTTdp Fibre To The distribution point
FTTP Fibre To The Premises
ETSI
7 ETSI TS 101 548 V1.1.1 (2014-09)
FTU FAST Transceiver Unit
NOTE: See Recommendation ITU-T G.9700 [i.6].
FTU-O FTU at the DPU
FTU-R FTU at the remote site
GPON Gigabit Passive Optical Network
HON Higher Order Node
LPF Low Pass Filter
LR Long Range
ME Management Entity
NMS Network Management System
NT Network Termination
NTE Network Termination Equipment
NTU Network Terminating Unit
OAM Operations And Maintenance
OLT Optical Line Termination
ONU Optical Network Unit
PD Powered Device
PDU Power Distribution Unit
PE Power Extraction
PHY Physical (layer)
PME-C CPE's Power Management Entity
PME-D DPU's Power Management Entity
PMT Power Management Transceiver
PoDL Power over Data Line
POTS Plain Old Telephony Service
PS Power Splitter
PSE Power Sourcing Equipment
PSU Power Supply Unit/Combiner
PWD PoWereD
RDY Ready
RFT Remote Feed Telecommunication
RPCE Reverse Power Control Entity
RPD Remote Powered Device
RPF Reverse Power Feed
RPFA-DRP Reverse Power Feed Architecture - Derived POTS
RPFA-DRPSW Reverse Power Feed Architecture - Derived POTS Sharing in-premises Wiring
RPFA-EXP Reverse Power Feed Architecture - Exchange POTS
RPFA-EXPSW Reverse Power Feed Architecture - Exchange POTS Sharing in-premises Wiring
RPFA-NOP Reverse Power Feed Architecture - No POTS
SELV Safety Extra Low Voltage
SG Service Gateway
SR Short Range
SS Service Splitter
SU Service Unit
TNV Telecommunication Network Voltage
VA Volt Ampere
VDSL Very high speed Digital Subscriber Line
VoIP Voice over Internet Protocol
VTU VDSL2 Transceiver Unit
NOTE: See Recommendation ITU-T G.993.2 [i.4].
VTU-O VTU at the ONU
VTU-R VTU at the remote site
xDSL Unspecified DSL variant
xTU-O FTU-O or VTU-O
xTU-R FTU-R or VTU-R
ETSI
8 ETSI TS 101 548 V1.1.1 (2014-09)
4 Introduction to Reverse Power Feed
4.1 Introduction
The basic architecture of a fibre-fed remote node with reverse power feed is shown below in Figure 1.

Figure 1: Generic Fibre-fed Remote Node Architecture with reverse power feed
Figure 1 shows power being injected at the NTE from a local power source (located within the home and/or building)
which traverses the local loop to power a fibre-fed remote node which can be located at either the distribution
point (DP) or cabinet using the same copper pair cable that is used to transmit the xDSL to/from the home/fibre-fed
remote node. A metallic POTS service is shown at the NTE. Voice services can also be implemented as a derived
service from the service gateway (SG).
An issue with regards to reverse powered fibre-fed nodes is that of who or what is responsible for the powering of
common circuitry contained within the node. It is easy to envisage that an individual user should be responsible for the
powering of the remote line terminating/driver electronics corresponding to his particular circuit. However, it is not so
easy to determine who or what is responsible for powering of say the ONU that terminates the fibre link.
There may be occasions where only a single user is providing power to the remote node but this may not be sufficient to
power all of the remote node electronics for proper operation. Also, there may be occasions where say a GPON feed
requests a response from the ONU (for ranging or management purposes) when no users are currently connected and
providing electrical power.
It is recognized that one single (i.e. generic) specification cannot consider all possible architectural variants, therefore
the present document has been organized as a series of architecture options and equipment shall adhere to one or more
of these options.
ETSI
9 ETSI TS 101 548 V1.1.1 (2014-09)
5 Reverse Power Feed Architecture
5.1 Introduction
There shall be compatibility with other architectures such as forwards powering of remote equipment from the CO or
the provision of local mains powering.
Service Providers may provide options for power back-up capability at the remote node and/or the customer premises. It
shall be possible to combine these power-feed options, for example when there is not enough power to operate a remote
node by reverse powering from a single customer alone. Under such circumstances it shall be possible to augment this
power with forwards power from the CO or local mains derived power.
Reverse powering shall have a power splitter (located at the customer premises and another at the remote node) to
enable power to be inserted at the customer end of a link and extracted at the remote node. The power splitter performs
a frequency splitting and combining function between the services being carried (which can include POTS and xDSL
based services) and the injected DC electrical power. The power splitter shall have an upper frequency limit for
powering of 300 Hz. In the case of POTS services being carried over the same metallic loop, and considering the
emergence of wideband POTS services for high quality voice, the cut-over frequency of the reverse power feed power
splitter should be in the order of 10 Hz or less.
Within the remote node, if it operates with multiple power-fed lines then there shall be a power extraction and combiner
unit. The purpose of this unit is to combine the multiple power feed input to produce a single power source output. A
fair power-sharing algorithm shall exist where the power load is fairly shared amongst the input power sources.
The technical specifications in the present document shall apply to each architecture described below as one of the five
options shown in Table 1.
Table 1: Architecture Options for Reverse Power Feed
Option Name Description
1 RPFA-NOP Reverse Power Feed Architecture - No POTS
2 RPFA-EXP Reverse Power Feed Architecture - Exchange POTS
3 RPFA-EXPSW Reverse Power Feed Architecture - Exchange POTS Sharing in-premises Wiring
4 RPFA-DRP Reverse Power Feed Architecture - Derived POTS
5 RPFA-DRPSW Reverse Power Feed Architecture - Derived POTS Sharing in-premises Wiring

5.2 Reverse Power Feed and POTS Co-Existence
5.2.1 Background
Table 1, option 2 to option 5 involve reverse power feed co-existing with POTS - whether this is exchange based POTS
(RPFA-EXP, RPFA-EXPSW) or derived POTS (RPFA-DRP, RPFA-DRPSW).
When a POTS service is present on the same wires as reverse power feed (option 2, option 3 and option 5) the POTS
DC signalling/low frequency signalling will be translated so that it uses another part of the baseband spectrum, but the
basic analogue voice signal remains essentially untouched. At the CPE, the signalling is restored and POTS is presented
as normal.
When POTS is provided by derived voice service (option 4 and option 5), low power (L2) modes may be used to
provide the voice service even when the entire payload is not required by other services. The CPE presentation may be
either an analogue presentation via an ATA or directly to a VoIP handset.
In order to achieve co-existence between reverse power feed and POTS various adaptors are required as described in
clause 5.2.2 for use in the reverse power feed reference models.
ETSI
10 ETSI TS 101 548 V1.1.1 (2014-09)
5.2.2 POTS Adapters
The following three different types of POTS adaptor are specified for use in the reverse power feed reference models:
1) POTS Adapter - E (POTSA-E)
2) POTS Adapter - C (POTSA-C)
3) POTS Adapter - D (POTSA-D)
Where reverse power feed and POTS signals traverse the same copper wires a signalling system shall be implemented
to allow the signalling at the POTS interface based on off-hook/on-hook DC impedance, and in those jurisdictions
requiring it, line reversal for Calling Number ID alerting to be communicated across the copper pair from the DPU to
the POTS terminals. This functionality can be provided by the various POTS adaptors described below.
5.2.2.1 POTS Adapter - E (POTSA-E)
POTS Adapter - E is the single adapter located at the DPU and this adapter shall perform the following functions:
1) Translate the downstream DC and low frequency POTS signalling into an in-band or out-of-band signalling
system.
2) Translate the signals from the upstream in-band or out-of-band signalling system into DC and low frequency
POTS signalling.
POTSA-E may provide a relay by-pass when un-powered (for life-line operation) or when signalled to provide direct
access to the exchange to allow operations such as line-test to be performed.
5.2.2.2 POTS Adapter - C (POTSA-C)
POTS Adapter - C is the single adapter located at the NT module and this adapter shall perform the following functions:
1) Translate the upstream DC and low frequency POTS signalling from the POTS Terminal into an in-band or
out-of-band signalling system.
2) Translate the downstream in-band or out-of-band signalling system into POTS signalling towards the POTS
Terminal.
3) Provide sufficient current limit and DC voltage to supply one or more phone devices.
4) Provide a pre-defined rate of change of current increase when a phone device goes off-hook to allow for the
detection of phone devices going off-hook that do not have the correct POTS adapter fitted.
POTSA-C may provide relay by-pass when un-powered (for lifeline operation) or when signalled to provide direct
access to the exchange to allow operations such as line-tests to be performed.
5.2.2.3 POTS Adapter - D (POTSA-D)
POTS Adapter - D is the adapter that can be attached to every phone device connected to the in-premises wiring on the
home network. This adapter operates in the presence of reverse powering. This adapter shall perform the following
function:
1) Translate the signals from the upstream DC and low frequency POTS signalling from the POTS Terminal
into an in-band or out-of-band signalling system.
2) Translate the signals from the downstream in-band or out-of-band signalling system into POTS signalling
towards the POTS Terminal.
3) Provide sufficient current limit and DC voltage to supply a single phone device.
4) Provide a pre-defined rate of change of current increase when a phone device goes off-hook to allow for the
detection of phone devices going off-hook that do not have the correct POTS adapter fitted.
ETSI
11 ETSI TS 101 548 V1.1.1 (2014-09)
5.3 Reverse Power Feed Architecture without POTS on the
same pair (RPFA-NOP)
The functional reference model of the reverse power feed architecture without POTS on the same pair (RPFA-NOP) is
shown in Figure 2. In this option, the reference model illustrates the RPF architecture with the broadband service only
and no underlying narrowband service, neither exchange-based POTS nor derived POTS.
The xTU-O is located inside the Distribution Point Unit (DPU) at the network side of the wire pair (U-O reference
point). The xTU-R is located inside the Network termination (NT) at the customer premises side of the wire pair (U-R
reference point). Each DPU is located at a distribution point and can contain one or more xTU-O transceivers (xTU-O-I,
I = 1…N), with each transceiver connected to an NT.
At the backhaul link termination, the PHY blocks represent the physical layer of the xTU-O module towards the access
network and of the NT towards the customer premises (CP). These blocks are shown for completeness of the data flow
but are out of scope of the present document. The L2+ blocks represent the Layer 2 and above functionalities contained
in the xTU-O module and the NT. These blocks are shown for completeness of the data flow but are out of scope of the
present document.
The traffic from all DPUs is aggregated by a backhaul transmission system operating over the Distribution Network
(DN) and Higher Order Node (HON) up to the V reference point. The type of transmission system is out of scope of the
present document.
The management of a DPU is performed by the network management system (NMS), passing management information
to the DPU's management entity (DPU ME) over a management communications channel that is provided over the
backhaul transmission system. The details of the management communications channel and most of the management
functionality required for the DPU are out of scope of the present document.
As there is a need for management transactions between the DPU and the CPE for controlling the start-up of reverse
powering to the DPU when mains power is applied to the CPE and for monitoring powering in normal operations,
power management transceivers are connected to the copper drop in the DPU (PMT-I, I = 1…N) and the customer
premises (PMT) to support a management protocol. The management information is exchanged between the PMT-I and
DPU ME through the power management entity PME-D. At the customer premises, the information flow takes place
between the PMT and CPE ME through the power management entity PME-C.
The power is inserted on the line (i.e. copper pair) by the Power Source Equipment (PSE) located in the customer
premises and extracted from the line by the Power Extractor (PE-I, I = 1…N) located in the DPU. Power is extracted
from each active port and combined in the Power Supply Unit (PSU) and coordinated over all lines by the Reverse
Power Control Entity (RPCE). The PE and PSU are separated from the broadband signal on the line (at reference point
U-O and U-R) by a power splitter (PS). Reverse power battery backup at the PDU and customer premises is illustrated
in block BAT.
ETSI
12 ETSI TS 101 548 V1.1.1 (2014-09)
DPU Customer Premises Equipment (CPE)
xTU-O module NT module
U-R
U-O
T/S
V
xTU-O-N d
d n
Copper
n
a
a
b
pair
b
d
xTU-O -1 PHY
d HON PHY L2+ xTU-R L2+
DN a
a o
PS -N
r
o
r
B
B
PS-1
PS
U-O2P
U-R2P
MT-N PE -N
PMT-1 PE-1
PMT PME-C
PSE
S
DPU
M PME-D RPCE PSU
CPE
N ME
BAT ME
BAT
Figure 2: RPFA-NOP Reference Model
Table 2: RPFA-NOP Reference Points
Reference Point Broadband Signals Reverse Power Analogue Voice Out of band POTS
Feed Signals Signalling
U-O2P No Yes No No
U-O /U-R Yes Yes No No
U-R2P No Yes No No
5.4 Reverse Power Feed Architecture with Baseband POTS
from the Exchange (RPFA-EXP)
The functional reference model of the reverse power feed architecture with baseband POTS from the exchange
(RPFA-EXP) is shown in Figure 3 and Figure 4.
This option includes two different variants. Figure 3 illustrates the case where a dedicated POTS port is used to connect
a single POTS device while the remaining customer premises equipment CPE (power splitter (PS), service splitter (SS),
power source equipment (PSE) and NT module) may be located anywhere on the in-premises wiring. The single POTS
adapter (POTSA-C) is also located at the same place as the rest of the CPE.
The second variant shown in Figure 4, illustrates the case where the CPE (power splitter (PS), service splitter (SS),
power insertion (PSE) and NT module) and the POTSA-C adapter are installed at the master-socket location while
multiple POTS devices are connected to the existed in-premises wiring.
In both cases it is expected that baseband voice is transmitted between the DPU and the customer premises and the
function of the POTS adapter in the DPU (POTSA-E) and POTS adapter in the customer premises (POTSA-C) is
concerned with the POTS signalling translation. Also in both cases, there is no requirement for an individual POTSA-D
to be attached to each individual phone device within the customer premises.
ETSI
13 ETSI TS 101 548 V1.1.1 (2014-09)
DPU
Customer Premises Equipment (CPE)
R
d
n
a
U-O2O U-R2S
b
S
POTSA
w POTSA
T
o
O
r -C
-E
P
r
a
N
SS
SS
xTU-O module
NT module
U-O
U-R T/S
U-R2
V xTU-O-N d
PS-N
d
n
Copper
n
a
a b
pair
b
d
xTU-O-1 PHY
d HON PHY L2+ PS-1 xTU-R L2+
DN PS a
a
o
r
o
r
B
B
U-O2
U-O2P
U-R2P
MT-N PE-N
PMT PME-C
PSE
PMT-1 PE-1
CPE
BAT ME
S
DPU
M PME-D RPCE PSU
N ME
BAT
Figure 3: RPFA-EXP Reference Model
DPU Customer Premises Equipment (CPE)
In-premises
R
d
n
wiring
a
U-O2O U-R2S
b S
POTSA
POTSA T
w
o O
r -C P
-E
r
a
N
S
T
O
SS SS
P
xTU-O module NT module
U-O
U-R T/S
U-R2
V
xTU-O-N d
PS-N
d
n
Copper
n a
a
b
pair
b
d
xTU-O-1 xTU-R L2+ PHY
d HON PHY L2+ PS-1
DN PS a
a o
o r
r
B
B
U-O2
U-O2P
U-R2P
MT-N PE-N
PMT PME-C
PSE
PMT-1 PE-1
CPE
BAT ME
S
DPU
M PME-D PSU
RPCE
N ME
BAT
Figure 4: RPFA-EXP Reference Model with multiple POTS
distributed over In-Premises Wiring
ETSI
14 ETSI TS 101 548 V1.1.1 (2014-09)
Table 3: RPFA-EXP Reference Points
Reverse Power Analog Voice Out of band POTS
Reference Point Broadband Signals
Feed Signals Signalling
U-O2 Yes No No No
U-O2O No No Yes Yes
U-O2P No Yes No No
U-O /U-R Yes Yes Yes Yes
U-R2P No Yes No No
U-R2S No Yes (see note) Yes Yes
U-R2 Yes No No No
NOTE: The POTSA-C adapter needs power for signalling conversion and will usually be locally powered if it is
collocated with the PSE, but it needs access to RPF to detect its presence and may optionally be powered by
RPF.
5.5 Reverse Power Feed Architecture with Baseband POTS
from the Exchange Sharing the in-premises Wiring
(RPFA-EXPSW)
The functional reference model of the reverse power feed architecture with baseband POTS from the exchange sharing
the in-premises wiring (RPFA-EXPSW) is shown in Figure 5. In this application, each POTS device connected to the
in-premises network is connected to an individual POTSA-D which provides POTS signalling translation. This
reference model is used when a traditional voice solution is utilized but an analogue POTS presentation is required over
the in-premises wiring including all extension wiring.
DPU
Customer Premises Equipment (CPE)
In-premises
R
wiring S
d POTSA
T
n
a
-D O
U-O2O
b P
w POTSA
o
r
-E
r
POTSA S
a
T
N
-D O
P
SS
SS
xTU-O module NT module
U-O U-R
U-R2 T/S
V
xTU-O-N d
PS-N
d
n
Copper
n a
a
b
pair
b
d
xTU-O-1 xTU-R L2+ PHY
d HON PHY L2+ PS-1
DN PS a
a
o
o r
r
B
B
U-O2
U-O2P U-R2P
MT-N PE-N
PMT PME-C
PSE
PMT-1 PE-1
CPE
BAT ME
S
DPU
M PME-D RPCE PSU
N ME
BAT
Figure 5: RPFA-EXPSW Reference Model
ETSI
15 ETSI TS 101 548 V1.1.1 (2014-09)
Table 4: RPFA-EXPSW Reference Points
Reverse Power Analog Voice Out of band POTS
Reference Point Broadband Signals
Feed Signals Signalling
U-O2 Yes No No No
U-O2O No No Yes Yes
U-O2P No Yes No No
U-O /U-R Yes Yes (see note) Yes Yes
U-R2P No Yes No No
U-R2 Yes No No No
NOTE: RPF provides power for signalling conversion.

It should be noted that the use cases for RPFA-EXP and RPFA-EXPSW may be combined so that POTSA-C and
POTSA-D may both be present.
5.6 Reverse Power Feed Architecture with Derived POTS
(RPFA-DRP)
The functional reference model of the reverse power feed architecture with derived POTS (RPFA-DRP) is shown in
Figure 6 and Figure 7.
Similar to the RPFA-EXP architecture defined in clause 5.4, this option includes two different variants. Figure 6
illustrates the case when the CPE (power splitter (PS), power source equipment (PSE) and NT module) may be located
anywhere on the in-premises wiring while a single analogue POTS interface is available on the dedicated line (i.e.
POTS service uses one wire pair while the DSL service uses another wire pair). The second variant is shown in Figure 7
illustrates the case where the CPE is installed at the master-socket location and multiple POTS interfaces are distributed
over the in-premises wiring. In this architecture, an analogue presentation of a VoIP service is provided at the CPE via
an Analogue Terminal Adapter (ATA). Other application models are possible, where the ATA is connected to a
cordless phone or a wireless phone device. The ATA can be integrated with the router in the same physical box NT1, or
with the NT module. Such a scheme is inherently simpler than the POTS solutions described in clause 5.4 because there
is no requirement for service splitter and POTS adapters. However, this solution proves to be the most difficult to
arrange for POTS failover during power outages at the CPE. Such a solution is dependent upon local battery power at
the CPE being able to also power the remote node (albeit the remote node may be operating in a low-power mode).
DPU Customer Premises Equipment (CPE)
R
NT1
POTS
ATA
xTU-O module NT module
T/S
U-O
U-O2 U-R
V
xTU-O-N
PS -N d
d
Copper n
n
a
a
b
pair
b
d
PHY L2+ xTU-O-1 xTU-R L2+ PHY
d HON DN PS-1
PS a
a
o
o r
r
B
B
U-O2P U-R2
U-R2P
MT-N PE-N
PMT PME-C
PSE
PMT-1 PE-1
CPE
BAT ME
S
DPU
M PME-D RPCE PSU
N ME
BAT
Figure 6: RPFA-DRP Reference Model with derived POTS and a single POTS port
ETSI
16 ETSI TS 101 548 V1.1.1 (2014-09)
DPU Customer Premises Equipment (CPE)
In-premises
R wiring
POTS
POTS
NT1
ATA
xTU-O module NT module
T/S
U-O
U-O2 U-R
U-R2
V xTU-O -N d
PS-N
d
n
n Copper
a
a
b
pair
b d
PHY
d HON PHY L2+ xTU-O-1 xTU-R L2+
DN PS-1 PS a
a o
o r
r
B
B
U-O2P
U-R2P
MT-N PE-N
PMT PME-C
PSE
PMT-1 PE-1
CPE
BAT
ME
S DPU
M PME-D PSU
RPCE
N ME
BAT
Figure 7: RPFA-DRP Reference Model with derived POTS distributed
over In-Premises Wiring
Table 5: RPFA-DRP Reference Points
Analogue Voice
Reference Point Broadband Signals Reverse Power Feed
Signals
U-O2 Yes No No
U-O2P No Yes No
U-O /U-R Yes Yes No
U-R2P No Yes No
U-R2 Yes No No
5.7 Reverse Power Feed Architecture with Derived POTS
Sharing the in-premises Wiring (RPFA-DRPSW)
The functional reference model of the reverse power feed architecture with derived POTS sharing the in-premises
wiring (RPFA-DRPSW) is shown in Figure 8. In this application, POTS is carried as a derived voice stream within the
broadband data. The voice stream is extracted via a router and then presented to a POTS adapter via an ATA. The
voiceband POTS signal is injected onto the in-premises wiring via the voice-frequency path through the service splitter
(SS). Because there is DC powering present on the in-premises wiring, it is not possible to include DC POTS signalling
and therefore a POTSA-D is required for every POTS device that is not collocated with the NT module.
ETSI
17 ETSI TS 101 548 V1.1.1 (2014-09)

Figure 8: RPFA-DRPSW Reference Model
Table 6: RPFA-DRPSW Reference Points
Broadband Analogue Voice Out Of Band POTS
Reference Point Reverse Power Feed
Signals Signals Signalling
U-O2 Yes No No No
U-O2P No Yes No No
U-O /U-R Yes Yes (see note 1) Yes Yes
U-R2P No Yes No No
U-R2S No Yes (see note 2) Yes Yes
U-R2 Yes No No No
NOTE 1: RPF provides power for signalling conversion.
NOTE 2: The POTSA-E adapter needs power for signalling conversion and is usually locally powered if it is collocated
with the PSE, but it needs access to RPF to detect its presence and may optionally be powered by RPF.

It should be noted that the use cases for RPFA-DRP and RPFA-EXPSW may be combined so that a POTS port and
POTSA-D may both be present.
6 Reverse Power Feed Start-Up Protocol
6.1 Introduction
As shown in clause 5, Reverse Power Feed can be applied either in conjunction with a baseband POTS service from a
CO, or with a derived POTS service, or without any POTS service.
ETSI
18 ETSI TS 101 548 V1.1.1 (2014-09)
In any scenario, a procedure shall be followed to guarantee proper interaction between the elements of the RPF system
(DPU - PSE - POTS adapters in the in-premises network). The procedure shall allow a proper start-up of RPF, and
should cover all further states of the RPF system (operation, shut down, error conditions). There are several possibilities
for implementing this, including a communications based start-up protocol and a metallic detection based start-up
protocol. A communications based start-up protocol is specified below.
NOTE: An example of a metallic detection based start-up protocol can be found in IEEE 802.3 [i.1].
If reverse powering is present on the in-premises network it is important to detect directly connected off-hook phones
and prevent them from becoming a safety hazard. If a directly connected off hook telephone is detected, a back off
mechanism shall be initiated for the reverse powering.
6.2 Communications-based Start-up (CBSU) Protocol
Exchanges of signalling messages supporting the CBSU protocol are defined in Table 7.
Table 7: Signalling messages for CBSU protocol
Message From > To Use
REQ
PSE > DPU PSE requests DPU to prepare for RPF
(Request)
RDY DPU indicates it has switched the line from bypass to RPF mode and is
DPU > PSE
(Ready) ready to receive RPF
PWD
DPU > PSE Keep-alive message sent by DPU
(Powered)
PSE > DPU (and
ACT Keep-alive message sent by PSE
dongles since on
(Active) Trigger for the dongles to become (and stay) active
same line)
The start-up protocol is described in the flow chart in Figure 9.
DPU (line N) PSE (line N) PA-D (1 to 4 per line) or single PA-C
Quiescent
Quiescent
(line not powered)
(no power injection)
Default connectivity line N:
POTS Discovery
Bypass mode (for lifeline)
Quiescent
(no power injection)
(Voice adaptor not active)
Listen for REQ
Detection of POTS off-hook
Yes
voltage on line
REQ REQ
Default connectivity =
Line Conditioned
No
pass-through mode
Connectivity line N:
(for lifeline)
REQ
CO Disconnection Discovery
switch from bypass to RPF mode
time-out
(no power injection)
Yes
Detection of any voltage on line
REQ
REQ
No
RDY RDY
RDY
if PSE only power source of DPU,
only when low power from PSE
Low Power Mode
Inactive
REQ (Voice adaptor not active)
Off-hook phone, or
REQ Low Power mode Check presence of RDY
RDY time-out
time-out Check no directly connected
Upon RDY, disconnect
Connectivity line N: RPF mode off-hook phone on line
pass-through connectivity
ACT Checks are OK
ACT
Reverse Powering Mode
ACT ACT
Reverse Powered mode
Active
(DSL active)
Apply RPF
PWD Check no directly connected
Error Error Pass-through connectivity
Connectivity line N: RPF mode Error
off-hook phone on line
disconnected
“Error” = one or multiple of:
“Error” = one or multiple of:
“Error” = one or multiple of:
No RPF on line N
Off-hook phone detected
No RPF (PSE down or not active)
Connectivity lost with PSE on line N
PSE switched off
Connectivity lost with DPU
Operator-controlled ceasing of RPF on line N
Connectivity lost with DPU
Figure 9: Flow-chart for CBSU protocol
ETSI
19 ETSI TS 101 548 V1.1.1 (2014-09)
A basic description of the flow chart for the case of Reverse Power Feed with POTS from the exchange
(RPFA-EXP or RPFA-EXPSW) is as follows:
1) The PSE first checks that there is no off-hook phone, then signals that it requests to apply RPF by sending
REQ message [POTS Discovery state], and waits for the absence of any voltage on the line [CO Disconnection
Discovery state]. This REQ message is the start of the handshaking between PSE and DPU.
2) In case of an on-going call the PSE should return to the Quiescent state and wait for an on-going call to end.
NOTE: The REQ message is only sent after the off-hook voltage disappears, so that an on-going call is not
interrupted.
3) The REQ message shall be detected by the DPU [Quiescent state], upon which the DPU interrupts the
connection of the line to the CO side (e.g. by switching a relay) [Line conditioned state]:
- In the [Quiescent] and [Line Conditioned] states (coloured in the figure), the DPU shall have some
(limited) bootstrap power to perform these actions. The POTS signal is still on the line. If there is no
local power source available at the DPU (such as a battery), in order to avoid conflict of DC power from
the PSE with DC power from the POTS, the DPU shall get some limited (parasitic) power from
...