EXHIBIT 9

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International Telecommunication Union

ITU-T G.984.1

TELECOMMUNICATION 

STANDARDIZATION SECTOR 

OF ITU

(03/2008) 

SERIES G: TRANSMISSION SYSTEMS AND MEDIA, 

DIGITAL SYSTEMS AND NETWORKS 

Digital sections and digital line system – Optical line 

systems for local and access networks 

Gigabit-capable passive optical networks 

(GPON): General characteristics 

Recommendation ITU-T G.984.1 

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ITU-T G-SERIES RECOMMENDATIONS 

TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS 

INTERNATIONAL TELEPHONE CONNECTIONS AND CIRCUITS G.100–G.199 

GENERAL CHARACTERISTICS COMMON TO ALL ANALOGUE CARRIERTRANSMISSION SYSTEMS G.200–G.299 

INDIVIDUAL CHARACTERISTICS OF INTERNATIONAL CARRIER TELEPHONE 

SYSTEMS ON METALLIC LINES 

G.300–G.399 

GENERAL CHARACTERISTICS OF INTERNATIONAL CARRIER TELEPHONE SYSTEMS 

ON RADIO-RELAY OR SATELLITE LINKS AND INTERCONNECTION WITH METALLIC 

LINES 

G.400–G.449 

COORDINATION OF RADIOTELEPHONY AND LINE TELEPHONY G.450–G.499 

TRANSMISSION MEDIA AND OPTICAL SYSTEMS CHARACTERISTICS G.600–G.699 

DIGITAL TERMINAL EQUIPMENTS G.700–G.799 

DIGITAL NETWORKS G.800–G.899 

DIGITAL SECTIONS AND DIGITAL LINE SYSTEM G.900–G.999 

General G.900–G.909 

Parameters for optical fibre cable systems G.910–G.919 

Digital sections at hierarchical bit rates based on a bit rate of 2048 kbit/s G.920–G.929 

Digital line transmission systems on cable at non-hierarchical bit rates G.930–G.939 

Digital line systems provided by FDM transmission bearers G.940–G.949 

Digital line systems G.950–G.959 

Digital section and digital transmission systems for customer access to ISDN G.960–G.969 

Optical fibre submarine cable systems G.970–G.979 

Optical line systems for local and access networks G.980–G.989 

Access networks G.990–G.999 

QUALITY OF SERVICE AND PERFORMANCE – GENERIC AND USER-RELATED 

ASPECTS 

G.1000–G.1999 

TRANSMISSION MEDIA CHARACTERISTICS G.6000–G.6999 

DATA OVER TRANSPORT – GENERIC ASPECTS G.7000–G.7999 

PACKET OVER TRANSPORT ASPECTS G.8000–G.8999 

ACCESS NETWORKS G.9000–G.9999 

For further details, please refer to the list of ITU-T Recommendations.

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 Rec. ITU-T G.984.1 (03/2008) i 

Recommendation ITU-T G.984.1 

Gigabit-capable passive optical networks (GPON): General characteristics 

Summary 

Recommendation ITU-T G.984.1 describes a flexible optical fibre access network capable of 

supporting the bandwidth requirements of business and residential services and covers systems with 

nominal line rates of 2.4 Gbit/s in the downstream direction and 1.2 Gbit/s and 2.4 Gbit/s in the 

upstream direction. Both symmetrical and asymmetrical (upstream/downstream) gigabit-capable 

passive optical network (GPON) systems are described. This Recommendation proposes the general 

characteristics for GPON based on operators' service requirements. 

Source 

Recommendation ITU-T G.984.1 was approved on 29 March 2008 by ITU-T Study Group 15 

(2005-2008) under Recommendation ITU-T A.8 procedure. 

 

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ii Rec. ITU-T G.984.1 (03/2008) 

FOREWORD 

The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of 

telecommunications, information and communication technologies (ICTs). The ITU Telecommunication 

Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying technical, 

operating and tariff questions and issuing Recommendations on them with a view to standardizing 

telecommunications on a worldwide basis. 

The World Telecommunication Standardization Assembly (WTSA), which meets every four years, 

establishes the topics for study by the ITU-T study groups which, in turn, produce Recommendations on 

these topics. 

The approval of ITU-T Recommendations is covered by the procedure laid down in WTSA Resolution 1. 

In some areas of information technology which fall within ITU-T's purview, the necessary standards are 

prepared on a collaborative basis with ISO and IEC. 

NOTE 

In this Recommendation, the expression "Administration" is used for conciseness to indicate both a 

telecommunication administration and a recognized operating agency. 

Compliance with this Recommendation is voluntary. However, the Recommendation may contain certain 

mandatory provisions (to ensure e.g. interoperability or applicability) and compliance with the 

Recommendation is achieved when all of these mandatory provisions are met. The words "shall" or some 

other obligatory language such as "must" and the negative equivalents are used to express requirements. The 

use of such words does not suggest that compliance with the Recommendation is required of any party. 

INTELLECTUAL PROPERTY RIGHTS

ITU draws attention to the possibility that the practice or implementation of this Recommendation may 

involve the use of a claimed Intellectual Property Right. ITU takes no position concerning the evidence, 

validity or applicability of claimed Intellectual Property Rights, whether asserted by ITU members or others 

outside of the Recommendation development process. 

As of the date of approval of this Recommendation, ITU had not received notice of intellectual property, 

protected by patents, which may be required to implement this Recommendation. However, implementers 

are cautioned that this may not represent the latest information and are therefore strongly urged to consult the 

TSB patent database at http://www.itu.int/ITU-T/ipr/. 

© ITU 2009 

All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the 

prior written permission of ITU. 

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 Rec. ITU-T G.984.1 (03/2008) iii 

CONTENTS 

Page 

1 Scope ............................................................................................................................ 1 

2 References..................................................................................................................... 1 

3 Definitions .................................................................................................................... 2 

3.1 Terms defined elsewhere................................................................................ 2 

3.2 Terms defined in this Recommendation......................................................... 2 

4 Abbreviations and acronyms ........................................................................................ 3 

5 Architecture of the optical access network................................................................... 4 

5.1 Network architecture ...................................................................................... 4 

5.2 Reference configuration ................................................................................. 5 

6 Services, user-network interface and service node interface........................................ 6 

6.1 Services........................................................................................................... 6 

6.2 User-network interface (UNI) and service node interface (SNI) ................... 7 

7 Bit rate .......................................................................................................................... 7 

8 Logical reach ................................................................................................................ 7 

9 Physical reach ............................................................................................................... 7 

10 Differential fibre distance............................................................................................. 7 

11 Maximum mean signal transfer delay........................................................................... 7 

12 Split ratio ...................................................................................................................... 7 

13 Service overlay ............................................................................................................. 8 

14 Protection on the PON section...................................................................................... 8 

14.1 Possible switching types................................................................................. 8 

14.2 Possible duplex GPON configurations and characteristics ............................ 9 

14.3 Requirements.................................................................................................. 10 

14.4 Required information fields for OAM frame ................................................. 11 

15 Security......................................................................................................................... 11 

Appendix I – Examples of GPON services, architectures and service protocol stacks........... 12 

I.1 Services, UNIs and SNIs ................................................................................ 12 

I.2 Typical system architectures .......................................................................... 14 

I.3 Service protocol stacks................................................................................... 16 

Appendix II – External access network backup....................................................................... 27 

Appendix III – Dual-parenting resilience ................................................................................ 30 

Bibliography............................................................................................................................. 32 

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 Rec. ITU-T G.984.1 (03/2008) 1 

Recommendation ITU-T G.984.1 

Gigabit-capable passive optical networks (GPON): General characteristics 

1 Scope 

This Recommendation addresses the general characteristics of gigabit-capable passive optical 

network (GPON) systems in order to guide and motivate the physical layer and the transmission 

convergence layer specifications. The general characteristics include examples of services, 

user-network interfaces (UNIs) and service node interfaces (SNIs) that are requested by network 

operators. Also, this Recommendation shows the principle deployment configuration. 

As much as possible, this Recommendation maintains characteristics from [ITU-T G.982] and 

ITU-T G.983.x-series Recommendations. This is to promote backward-compatibility with existing 

optical distribution networks (ODNs) that complies with those Recommendations. 

GPON systems are characterized, in general, by an optical line termination (OLT) system and an 

optical network unit (ONU) or optical network termination (ONT) with a passive optical 

distribution network (ODN) interconnecting them. There is, in general, a one-to-many relationship 

between the OLT and the ONU/ONTs, respectively. 

2 References 

The following ITU-T Recommendations and other references contain provisions which, through 

reference in this text, constitute provisions of this Recommendation. At the time of publication, the 

editions indicated were valid. All Recommendations and other references are subject to revision; 

users of this Recommendation are therefore encouraged to investigate the possibility of applying the 

most recent edition of the Recommendations and other references listed below. A list of the 

currently valid ITU-T Recommendations is regularly published. The reference to a document within 

this Recommendation does not give it, as a stand-alone document, the status of a Recommendation. 

[ITU-T G.652] Recommendation ITU-T G.652 (2003), Characteristics of a single-mode 

optical fibre cable. 

[ITU-T G.808.1] Recommendation ITU-T G.808.1 (2006), Generic protection switching – 

Linear trail and subnetwork protection. 

[ITU-T G.902] Recommendation ITU-T G.902 (1995), Framework Recommendation on 

functional access networks (AN) – Architecture and functions, access types, 

management and service node aspects. 

[ITU-T G.982] Recommendation ITU-T G.982 (1996), Optical access networks to support 

services up to the ISDN primary rate or equivalent bit rates. 

[ITU-T G.983.1] Recommendation ITU-T G.983.1 (1998), Broadband optical access systems 

based on Passive Optical Networks (PON). 

[ITU-T G.983.2] Recommendation ITU-T G.983.2 (2002), ONT management and control 

interface specification for B-PON. 

[ITU-T G.983.3] Recommendation ITU-T G.983.3 (2001), A broadband optical access system 

with increased service capability by wavelength allocation. 

[ITU-T G.984.2] Recommendation ITU-T G.984.2 (2003), Gigabit-capable Passive Optical 

Networks (GPON): Physical Media Dependent (PMD) layer specification. 

[ITU-T G.984.3] Recommendation ITU-T G.984.3 (2008), Gigabit-capable Passive Optical 

Networks (GPON): Transmission convergence layer specification. 

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2 Rec. ITU-T G.984.1 (03/2008) 

[ITU-T G.984.4] Recommendation ITU-T G.984.4 (2008), Gigabit-capable Passive Optical 

Networks (GPON): ONT management and control interface specification. 

[ITU-T G.984.5] Recommendation ITU-T G.984.5 (2007), Gigabit-capable Passive Optical 

Networks (GPON): Enhancement band. 

[ITU-T I.112] Recommendation ITU-T I.112 (1993), Vocabulary of terms for ISDNs. 

3 Definitions 

This Recommendation makes frequent use of the terms defined in [ITU-T G.983.1] and 

[ITU-T G.983.3]; some terms have been added. For convenience, the main definitions related to the 

GPON service requirements are reported in this clause. 

3.1 Terms defined elsewhere 

This Recommendation uses the following terms defined elsewhere: 

3.1.1 service node interface (SNI): [ITU-T G.902] 

3.1.2 user-network interface (UNI): [ITU-T I.112] 

3.2 Terms defined in this Recommendation 

This Recommendation defines the following terms: 

3.2.1 adaptation function (AF): AF is additional equipment and/or function to change an 

ONT/ONU subscriber-side interface into the UNI. Functions of AF depend on the ONT/ONU 

subscriber-side interface and UNI interface. AF is also used to change an OLT network interface 

into the SNI interface that is required by an operator. 

3.2.2 differential fibre distance: An OLT is connected to several ONU/ONTs. The differential 

fibre distance is the difference in the distance between the nearest and furthest ONU/ONT from the 

OLT.

3.2.3 logical reach: Logical reach is defined as the maximum distance that can be achieved for a 

particular transmission system, regardless of the optical budget. 

3.2.4 mean signal transfer delay: The mean signal transfer delay is the average of the upstream 

and downstream delay values between reference points; this value is determined by measuring 

round-trip delay and then dividing by 2. 

3.2.5 optical access network (OAN): The OAN is the set of access links sharing the same 

network-side interfaces and supported by optical access transmission systems. The OAN may 

include a number of ODNs connected to the same OLT. 

3.2.6 optical distribution network (ODN): In the PON context, a tree of optical fibres in the 

access network, supplemented with power or wavelength splitters, filters or other passive optical 

devices. 

3.2.7 optical line termination (OLT): A device that terminates the common (root) endpoint of 

an ODN, implements a PON protocol, such as that defined by [ITU-T G.984], and adapts PON 

PDUs for uplink communications over the provider service interface. The OLT provides 

management and maintenance functions for the subtended ODN and ONUs. 

3.2.8 optical network termination (ONT): A single subscriber device that terminates any one of 

the distributed (leaf) endpoints of an ODN, implements a PON protocol, and adapts PON PDUs to 

subscriber service interfaces. An ONT is a special case of an ONU. 

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 Rec. ITU-T G.984.1 (03/2008) 3 

3.2.9 optical network unit (ONU): A generic term denoting a device that terminates any one of 

the distributed (leaf) endpoints of an ODN, implements a PON protocol, and adapts PON PDUs to 

subscriber service interfaces. In some contexts, an ONU implies a multiple-subscriber device. 

3.2.10 physical reach: Physical reach is defined as the maximum physical distance that can be 

achieved for a particular transmission system. 

3.2.11 service: Service is defined as a network service required by operators. Service is described 

by a name that is clearly recognized by everyone, regardless of whether it is a frame structure name 

or a general name. 

4 Abbreviations and acronyms 

This Recommendation uses the following abbreviations and acronyms: 

AF Adaptation Function 

BRI Basic Rate Interface 

DSL Digital Subscriber Line 

FTTB Fibre to the Building 

FTTC Fibre to the Curb 

FTTCab Fibre to the Cabinet 

FTTH Fibre to the Home 

ISDN Integrated Services Digital Network 

LT Line Terminal 

MDU Multi-Dwelling Unit 

NT Network Termination 

OAM Operation, Administration and Maintenance 

OAN Optical Access Network 

ODN Optical Distribution Network 

OLT Optical Line Termination 

ONT Optical Network Termination 

ONU Optical Network Unit 

OpS Operations System 

PDH Plesiochronous Digital Hierarchy 

PON Passive Optical Network 

POTS Plain Old Telephone Service 

PRI Primary Rate Interface 

PSTN Public Switched Telephone Network 

SDH Synchronous Digital Hierarchy 

SN Serial Number 

SNI Service Node Interface 

TC Transmission Convergence 

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4 Rec. ITU-T G.984.1 (03/2008) 

UNI User-Network Interface 

VOD Video On Demand 

WDM Wavelength Division Multiplexing 

5 Architecture of the optical access network 

5.1 Network architecture 

The optical section of a local access network system can be either active or passive and its 

architecture can be either point-to-point or point-to-multipoint. Figure 1 shows the architectures 

considered, which range from fibre to the home (FTTH), through fibre to the building/curb 

(FTTB/C) to fibre to the cabinet (FTTCab). The optical access network (OAN) is common to all 

architectures shown in Figure 1, hence the commonality of this system has the potential to generate 

large worldwide volumes. 

G.984.1_F1

Fibre

Fibre

Fibre

Copper

Copper

Home Access network

network

UNI SNI

ONU Optical Network Unit

ONT Optical Network Termination

OLT Optical Line Termination

NT Network Termination

FTTCab

FTTH

O

N

T

N

T

N

T

O

N

U

O

N

U

O

L

T

FTTB/C

Figure 1 – Network architecture 

The differences of the FTTB, FTTC, FTTCab and FTTH network options are mainly due the 

different services supported, so they can be treated the same in this Recommendation. 

5.1.1 FTTB scenario 

The FTTB scenario is divided into two scenarios, one for multi-dwelling units (MDUs) and the 

other for businesses. Each scenario has the following service categories. 

5.1.1.1 FTTB for MDU 

• Asymmetric broadband services (e.g., digital broadcast services, VOD, file download, etc.). 

• Symmetric broadband services (e.g., content broadcast, e-mail, file exchange, distance 

learning, telemedicine, online-gaming, etc.). 

• POTS and ISDN. The access network must be able to provide, in a flexible way, 

narrow-band telephone services with appropriate timing for the introduction. 

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 Rec. ITU-T G.984.1 (03/2008) 5 

5.1.1.2 FTTB for business 

• Symmetric broadband services (e.g., group software, content broadcast, e-mail, file 

exchange, etc.). 

• POTS and ISDN. The access network must be able to provide, in a flexible way, 

narrow-band telephone services with the appropriate timing for the introduction. 

• Private line services. The access network must be able to provide, in a flexible way, private 

line services at several rates. 

5.1.2 FTTC and FTTCab scenario 

Within this scenario, the following service categories have been considered: 

• Asymmetric broadband services (e.g., digital broadcast services, VOD, file download, 

online-gaming, etc.). 

• Symmetric broadband services (e.g., content broadcast, e-mail, file exchange, distance 

learning, telemedicine, etc.). 

• POTS and ISDN. The access network must be able to provide, in a flexible way, 

narrow-band telephone services with the appropriate timing for the introduction. 

• xDSL backhaul. 

5.1.3 FTTH scenario 

Within this scenario, the following service categories have been considered: 

• Asymmetric broadband services (e.g., digital broadcast services, VOD, file download, etc.). 

• Symmetric broadband services (e.g., content broadcast, e-mail, file exchange, distance 

learning, telemedicine, online-gaming, etc.). 

• POTS and ISDN. The access network must be able to provide, in a flexible way, 

narrow-band telephone services with the appropriate timing for the introduction. 

5.2 Reference configuration 

The reference configuration is shown in Figure 2. 

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6 Rec. ITU-T G.984.1 (03/2008) 

G.984.1_F2

Q

UNI R/S S/R SNI

V reference point T Reference point

Access Network System Management Functions 

Optical Splitter

OLT

WDM

NE

WDM

AF

NE

ODN

POINT A POINT B

(a) Reference point

Optical Network Unit

Optical Network Terminal

Optical Distribution Network

Optical Line Termination

Wavelength Division Multiplex Module (If WDM is not used, this function is not necessary.)

Network Element which uses the different wavelength from the OLT and the ONU

Adaptation Function (Sometimes, it may be included in the ONU.)

Service Node Interface

User Network Interface

Point on the optical fibre just after the OLT (Downstream)/ONU (Upstream) optical connection

point (i.e., optical connector or optical splice)

Point on the optical fibre just before the ONU (Downstream)/OLT (Upstream) optical connection

point (i.e., optical connector or optical splice)

If AF is included in the ONU, this point is not necessary.

If WDM is not used, these points are not necessary.

ONU

ONT

ODN

OLT

WDM

NE

AF

SNI

UNI

S

R

(a) Reference point

POINT A/B

Service

node

function

ONU/

ONT

IFPON IFPON

NOTE – Whether or not the AF is an operating object of the Q interface depends on the service. 

Figure 2 – Reference configuration for GPON 

5.2.1 Service node interface 

See [ITU-T G.902]. 

5.2.2 Interface at the reference points S/R and R/S 

The interface at reference points S/R and R/S is defined as IFPON. This is a PON-specific interface 

that supports all the protocol elements necessary to allow transmission between OLT and ONUs. 

6 Services, user-network interface and service node interface 

6.1 Services 

GPON is required to support all currently known services and new services being discussed for 

residential subscribers and business customers, because of such a broadband capability. 

What specific services should be provided is clearer to some operators than to others and depends 

heavily on the particular regulatory conditions of each operator's markets, as well as on the market's 

own potential. How these services are delivered in a cost-effective way is a function not only of 

legal conditions, but also of factors including existing telecommunication infrastructure, dwelling 

distribution, and residential and business customers mix. 

Some examples of services are described in clause I.1. 

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 Rec. ITU-T G.984.1 (03/2008) 7 

6.2 User-network interface (UNI) and service node interface (SNI) 

ONU/ONT has UNI, as well as OLT, has an SNI as described in Figure 2. UNI/SNI depends on 

which services are provided by the service operator. 

Some examples of UNI are described in clause I.2 and examples of SNI are described in clause I.3. 

7 Bit rate 

Basically, GPON aims at transmission speeds greater than or equal to 1.2 Gbit/s. Accordingly, 

GPON identifies two transmission speed combinations as follows: 

• 1.2 Gbit/s up, 2.4 Gbit/s down; 

• 2.4 Gbit/s up, 2.4 Gbit/s down. 

The most important bit rate is 1.2 Gbit/s up, 2.4 Gbit/s down, constituting nearly all of the deployed 

and planned deployment of the GPON systems. 

8 Logical reach 

Logical reach is the maximum distance between ONU/ONT and OLT except for the limitation of 

the physical layer. In GPON, the maximum logical reach is defined as 60 km. 

9 Physical reach 

Physical reach is the maximum physical distance between the ONU/ONT and the OLT. In GPON, 

two options are defined for the physical reach: 10 km and 20 km. It is assumed that 10 km is the 

maximum distance over which FP-LD can be used in the ONU for high bit rates such as 1.25 Gbit/s 

or above. 

10 Differential fibre distance 

In GPON, the maximum differential fibre distance is 20 km. This affects the size of the ranging 

window and provides compliance with [ITU-T G.983.1]. 

11 Maximum mean signal transfer delay 

GPON must accommodate services that require a maximum mean signal transfer delay of 1.5 ms. 

Specifically, GPON system must have a maximum mean signal transfer delay time of less than 

1.5 ms between T-V (or (a)-V, depending on the operator's preference). See clause 12 of 

[ITU-T G.982]. Delays introduced by the adaptation functions such as circuit emulation are not 

included in this value. 

Although a section of the delay measurement is T-V for FTTH system, or (a)-V for the other 

application in [ITU-T G.982], in a GPON system the reference points are not restricted by the 

system configuration. 

12 Split ratio 

Basically, the larger the split ratio is for GPON, the more attractive it is for operators. However, a 

larger split ratio implies greater optical splitting which creates the need for an increased power 

budget to support the physical reach. 

Split ratios of up to 1:64 are realistic for the physical layer, given current technology. However, 

anticipating the continued evolution of optical modules, the TC layer must consider split ratios up 

to 1:128. 

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8 Rec. ITU-T G.984.1 (03/2008) 

13 Service overlay 

An overlay wavelength may be used to provide enhanced services to the subscriber. Accordingly, 

GPON must vacate the Enhancement Band defined in [ITU-T G.983.3]. 

14 Protection on the PON section 

From the viewpoint of administration of the access network, the protection architecture of GPON is 

considered to enhance the reliability of the access networks. However, protection shall be 

considered as an optional mechanism because its implementation depends on the realization of 

economical systems. Further information on protection switching can be found in [ITU-T G.808.1]. 

This clause presents some possible duplex configurations and related requirements as examples of 

protected GPON systems. In addition, the required OAM message for protection is mentioned. 

14.1 Possible switching types 

There are two types of protection switching, both of which are analogous to those of SDH systems: 

i) automatic switching; and 

ii) forced switching. 

The first type is triggered by fault detection, such as loss of signal, loss of frame, signal degrade 

(BER becomes worse than the predetermined threshold), and so on. The second type is activated by 

administrative events, such as fibre rerouting, fibre replacement, etc. Both types should be possible 

in a GPON system, if required, even though they are optional functions. The switching mechanism 

is generally realized by the OAM function, therefore, the required OAM information field should be 

reserved in the OAM frame. 

Figure 3a shows the self-contained duplex system model for the access network. The relevant part 

of the protection in the GPON system in this scheme should be a part of the protection between the 

ODN interface in the OLT and the ODN interface in the ONU via the ODN, excluding the SNI 

redundancy in the OLT. 

G.984.1_F3

PON LT(1)

PON LT(0)

PON LT(1)

PON LT(0)

Switch

SNI LT(1)

ODN(0) SNI LT(0)

ODN(1)

S/R R/S

ONU

OLT

UNI

LT

Service

node

M

U

X

Figure 3a – Duplex system model 

Figure 3b shows the duplex system model for the dual-parented access network. The relevant part 

of the protection in the GPON system should be a part of the protection between the ODN interface 

in the ONU and each ODN interface in the two OLTs via the ODN, plus the signalling required to 

implement protection functions upstream from the SNI. 

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 Rec. ITU-T G.984.1 (03/2008) 9 

PON LT(1)

PON LT(0)

PON LT(1)

M

U

X

UNI

LT

Switch SNI LT(1)

PON LT(0) Switch SNI LT(0)

ODN(1)

S/R R/S

ONU

OLT

OLT

ODN(0)

Network

PON LT(1)

PON LT(0)

PON LT(1)

M

U

X

UNI

LT

Switch SNI LT(1)

PON LT(0) Switch SNI LT(0)

ODN(1)

S/R R/S

ONU

OLT

OLT

ODN(0)

Network

Figure 3b – Dual-parented duplex system model 

14.2 Possible duplex GPON configurations and characteristics 

There can be several types of duplex GPON systems, as shown in Figures 4a and 4b. The control 

protocols for each configuration should be specified independently from one another. 

For example, in Figure 4b, no switching protocol is required since the switching is carried out only 

in the OLT. 

14.2.1 Configuration examples 

Type A: A deprecated configuration that duplicated only the optical fibres. 

Type B: The second configuration (Figure 4a) doubles the OLTs and the optical fibres between the 

OLTs and the optical splitter, and the splitter has two input/output ports on the OLT side. This 

configuration reduces the cost of duplexing the ONUs, although only the OLT side can be 

recovered. 

Type C: The third configuration (Figure 4b) doubles not only the OLT side facilities but also the 

ONU side. In this configuration, recovery from failure at any point is possible by switching to the 

standby facilities. Therefore, the full duplex cost enables high reliability. 

Type D: A deprecated configuration that allowed the mixing of duplicated and non-duplicated 

ONUs, essentially providing a combination of types B and C protection. 

G.984.1_F4b

ONU #1

ONU #N

OLT

PON LT

PON LT

PON LT(0)

PON LT(1)

N:2 optical splitter

Figure 4a – Duplex GPON system: OLT-only duplex system 

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10 Rec. ITU-T G.984.1 (03/2008) 

G.984.1_F4c

PON LT(0)

PON LT(1)

PON LT(0)

PON LT(1)

OLT

PON LT(0)

PON LT(1)

ONU #1

ONU #N

Double

N:2 optical splitter

Figure 4b – Duplex GPON system: Full duplex system 

Note that in both of these types of protection schemes, the PON line terminations do not need to 

reside in a single OLT equipment. In fact, they may be located in physically diverse locations (dual 

parenting). The control of such a system is discussed in Appendix III. 

14.2.2 Characteristics 

Type B: This configuration requires cold standby of the spare circuit in the OLT side. In this case, 

signal loss or even frame loss is, in general, inevitable in the switching period. However, all the 

connections supported between the service node and the terminal equipment should be held after 

this switching. 

Type C: In this case, the hot standby of the spare receiver circuits is possible in both ONU and OLT 

sides. In addition, hitless switching (without frame loss) is also possible in this configuration. 

14.3 Requirements 

1) The protection switching function should be optional. 

2) Both automatic protection switching and forced switching are possible in the GPON 

system, if required, even though they are optional functions. 

3) All the configuration examples of clause 14.2 will be possible, even though they are 

optional functions. 

4) The switching mechanism is generally realized by the OAM function, therefore, the 

required OAM information field must be reserved in the OAM frame. 

5) All the connections supported between the service node and the terminal equipment should 

be held after switching. 

Regarding the last requirement, one implementation of the POTS service node (exchange) requires 

the frame loss period to be less than 120 ms. If the frame loss period becomes longer than that, the 

service node disconnects the call, and the call set-up is required again after the protection switching. 

Since GPON supports the emulation of conventional services, such as POTS and ISDN, this value 

should be taken into consideration. 

T1 and E1 services require 50 ms protection times, so for these services to be provided as protected, 

the GPON should support 50 ms protection times. 

Case 6:20-cv-00534-ADA Document 47-14 Filed 03/05/21 Page 17 of 44
 Rec. ITU-T G.984.1 (03/2008) 11 

14.4 Required information fields for OAM frame 

Protection switching requires less than ten codes to be used for both upstream and downstream, 

which will be realized by the field of the OAM frame. The field mapping of the OAM frame for the 

protection will be required to be defined. 

15 Security 

Due to the multicast nature of the PON, GPON needs a security mechanism adapting the following 

requirements: 

• To prevent other users from easily decoding the downstream data. 

• To prevent other users from masquerading as another ONU/ONT or user. 

• To allow cost-effective implementation. 

Case 6:20-cv-00534-ADA Document 47-14 Filed 03/05/21 Page 18 of 44
12 Rec. ITU-T G.984.1 (03/2008) 

Appendix I 

Examples of GPON services, architectures and service protocol stacks 

(This appendix does not form an integral part of this Recommendation) 

This appendix provides various examples of practical GPON system aspects. First, a review of the 

typical services a GPON system supports is given. Second, a selection of system architectures are 

illustrated. Third, the common protocol stack traces are laid out for all these services and systems. 

It should be noted that since GPON is so widely applicable, the total scope of all the variants is very 

large, and any single implementation will not implement all of the possible features. The object of 

this appendix is to only give a general overview for the family of systems. 

I.1 Services, UNIs and SNIs 

This clause describes some examples of services, UNI and SNI, which are required by operators. 

I.1.1 Examples of services 

Some examples of services that GPON are required to support are shown in Table I.1, along with 

relevant remarks. 

Table I.1 – Examples of services and related remarks 

Service category 

(Note 1) Service Remarks 

Data service Ethernet 

(Note 2)

Standardized in [b-IEEE 802.3]. 

Comply with [b-IEEE 802.1D]. 

POTS Mean signal transfer delay time between T-V (or (a)-V) should be less 

than 1.5 ms. If echo cancellation is used in the network, the mean 

signal transfer delay time between T-V (or (a)-V) on the PON-based 

system may be longer, provided end-to-end transfer delay 

requirements are met. 

Synchronize with the network clock (Note 3). 

Signal on the T reference point and V reference point must be 

continuous. 

ISDN (BRI) Bearer rate is 144 kbit/s. 

Mean signal transfer delay time between T-V (or (a)-V) should be less 

than 1.5 ms. 

Synchronize with the network clock (Note 3). 

PSTN 

ISDN (PRI) Bearer rate is 1.544 Mbit/s and 2.048 Mbit/s. 

Mean signal transfer delay time between T-V (or (a)-V) should be less 

than 1.5 ms. 

Synchronize with the network clock (Note 3). 

T1 Bearer rate is 1.544 Mbit/s. 

Mean signal transfer delay time between T-V (or (a)-V) should be less 

than 1.5 ms. 

Private Line 

E1 Bearer rate is 2.048 Mbit/s. 

Mean signal transfer delay time between T-V (or (a)-V) should be less 

than 1.5 ms. 

Case 6:20-cv-00534-ADA Document 47-14 Filed 03/05/21 Page 19 of 44
 Rec. ITU-T G.984.1 (03/2008) 13 

Table I.1 – Examples of services and related remarks 

Service category 

(Note 1) Service Remarks 

DS3 Bearer rate is 44.736 Mbit/s. 

E3 Bearer rate is 34.368 Mbit/s. 

Video Digital video Primary focus is on video over IP, with a QoS sufficient to support 

competitive viewing experience as compared to traditional transport 

methods. 

NOTE 1 – Service category is merely an index. It is not meaningful in itself, but it is useful in visualizing 

the services. 

NOTE 2 – Ethernet service is mainly to transmit data such as IP, which includes VoIP, video streams 

coded by MPEG-2 or MPEG-4, and so on. 

NOTE 3 – See [b-ITU-T G.810], [b-ITU-T G.813], [b-ITU-T G.8261], [b-ITU-T G.703] and 

[b-ITU-T G.8262]. 

I.1.2 Examples of UNI 

In this appendix, UNI is defined as the interface that includes the following conditions: 

• described by a well-known standard; 

• includes a physical layer aspect. 

Some UNIs are provided via an AF, so it is not mandatory that the ONU/ONT support those 

interfaces. 

Examples of UNIs, physical interfaces and services that they provide are shown in Table I.2. 

Table I.2 – Examples of UNI and services 

UNI (Note 1) Physical interface (Note 2) Service (Note 3) 

10BASE-T ([b-IEEE 802.3]) – Ethernet 

100BASE-TX ([b-IEEE 802.3]) – Ethernet 

1000BASE- T ([b-IEEE 802.3]) – Ethernet 

[b-ITU-T I.430] – ISDN (BRI) 

[b-ITU-T G.703] PDH DS3, ATM, E1, E3 

[b-ANSI T1.102], 

[b-ANSI T1.107] 

PDH T1, DS3 

NOTE 1 – There are many other services accommodated in GPON, but those services do not have 

specified UNIs. 

NOTE 2 – Each item in the "physical interface" column is illustrated by the corresponding entry in the 

"UNI" column. 

NOTE 3 – The column labelled "service" shows which services can be supported by the physical interface. 

I.1.3 Examples of SNI 

In this appendix, SNI is defined as the interface that includes the following conditions: 

• described by a well-known standard; 

• includes a physical layer aspect. 

Examples of SNIs, physical interfaces and services that they provide are shown in Table I.3. 

Case 6:20-cv-00534-ADA Document 47-14 Filed 03/05/21 Page 20 of 44
14 Rec. ITU-T G.984.1 (03/2008) 

Table I.3 – Examples of SNI and services 

SNI 

(Note 1) 

Physical interface 

(Note 2) 

Service 

(Note 3) 

1000BASE ([b-IEEE 802.3]) 

10000BASE ([b-IEEE 802.3]) 

– Ethernet 

[b-ITU-T G.965] V5.2 POTS, ISDN(BRI), ISDN(PRI) 

[b-ITU-T G.703] PDH, STM-1e DS3, ATM, E1, E3, STM-1, DS1 

[b-ITU-T G.957] STM-1, 4, 16 E1, E3, DS1, DS3, GFP, E4, STM-n, 

ATM 

[b-ANSI T1.107] PDH DS1, DS3 

[b-ANSI T1.105.06] 

[b-ANSI T1.117] 

OC3, OC12 DS1, DS3, ATM 

NOTE 1 – There are many other services accommodated in GPON, but those services do not have 

specified SNIs. 

NOTE 2 – Each item in the "physical interface" column is illustrated by the corresponding entry in the 

"SNI" column. 

NOTE 3 – The column labelled "service" shows which services can be supported by the physical interface. 

I.2 Typical system architectures 

Figure I.1 shows a generic GPON system. This is developed more specifically in Figures I.2 to I.7. 

OLT

ONU

/

ONT

ODN

SNI(s) CPE UNI(s)

Figure I.1 – Generic GPON system 

I.2.1 OLT variants 

Figure I.2 shows a pure-OLT option. In this case, the OLT equipment contains only the GPON 

adaptation function, and typically (but not necessarily) some level of Ethernet aggregation function. 

It is the simplest form of OLT, and avoids as many specific service linkages as possible. 

OLT

ONU

/

ONT

ODN

SNI CPE UNI(s)

Ether

Figure I.2 – Pure OLT scenario 

Case 6:20-cv-00534-ADA Document 47-14 Filed 03/05/21 Page 21 of 44
 Rec. ITU-T G.984.1 (03/2008) 15 

Figure I.3 shows a grooming OLT scenario. In this case, the OLT takes on additional 

service-grooming functions, typically including voice gateway and TDM circuit emulation 

functions. Note that these services can be provided using a 'pure OLT' and a separate voice 

gateway; however, as a practical matter, the integration of voice and TDM services seems to have 

strong economic and practical advantages. 

OLT

ONU

/

ONT

ODN

SNI CPE UNI(s)

DS1

Ether

Figure I.3 – Grooming OLT scenario 

I.2.2 ONU variants 

Figure I.4 shows the 'VDSL/POTS ONU' variant. The distinguishing feature of this variation is that 

the ONU is used to create copper-based interfaces just like a digital loop carrier/digital subscriber 

line access multiplexer (DLC/DSLAM) would do. There are two sub-types of this scheme. The first 

is where the ONU provides both POTS and VDSL interfaces to the customer, trying to centralize 

functions and reduce the need for CPE. The second is where the ONU provides VDSL-only 

interfaces, trying to minimize the ONU's size and power, albeit at the cost of requiring POTS 

derivation at the CPE. This alternative is useful mostly in FTTB and FTTC applications. 

OLT ODN ONU

SNI(s) CPE UNI(s)

CPE UNI(s) DSL

POTS

Figure I.4 – VDSL/POTS ONU scenario 

Figure I.5 shows the 'GPON modem' variant, where the ONT is made as small and simple as 

possible. In this case, it resembles a modem that provides Layer 1 and 2 interworking between the 

GPON optical interface and the data link technology. The data link then carries all service flows to 

the CPE, which does the bulk of the service interworking function. The popular data link 

technologies in use today are CAT5-based Ethernet, HPNA-over-coax and MoCA. This system is 

mostly used in FTTH applications. 

Case 6:20-cv-00534-ADA Document 47-14 Filed 03/05/21 Page 22 of 44
16 Rec. ITU-T G.984.1 (03/2008) 

OLT ODN ONT CPE

SNI(s) UNI(s)

Data

Link

Figure I.5 – GPON modem scenario 

Figure I.6 shows the 'integrated ONT' situation. This is can be thought of as the merger of the 

GPON modem and the service-deriving CPE in the previous diagram. However, this merging of 

functions has critical implications on which system is responsible for the management of the 

services. It should also be noted that even though significant functions have been incorporated into 

the ONT, a CPE is typically still placed in the home. This scenario is also popular for FTTH. 

OLT ODN ONT

SNI(s)

CPE

UNI(s)

Figure I.6 – Integrated ONT scenario 

Figure I.7 shows the 'residential gateway ONT' situation. This is can be thought of as the merger of 

the integrated ONT and the service-deriving CPE in the previous diagram. This draws Layer 3 

functionality into the ONT, including such items as routing, NAT and firewall functionality. This 

scenario is also popular for FTTH. 

OLT ODN ONT

SNI(s) UNI(s)

Figure I.7 – Residential gateway ONT scenario 

I.3 Service protocol stacks 

The following clauses present a listing of protocol stacks for the important service traces in GPON 

systems. By service, we mean the basic Layer 2-3 interfaces that have a major impact on the GPON 

equipment. Many high-layer services can ride on top of these interfaces; however, they tend not to 

Case 6:20-cv-00534-ADA Document 47-14 Filed 03/05/21 Page 23 of 44
 Rec. ITU-T G.984.1 (03/2008) 17 

have such a concrete impact on the GPON equipment, or at least not an impact any different than 

any other access system. 

I.3.1 Common functions 

The common GPON layers are shown in Figure I.8. [ITU-T G.984.2] specifies the GPON physical 

medium and the physical medium dependents (optics). [ITU-T G.984.4] defines the transmission 

convergence layer, which deals primarily with the construction of the transmission frame and the 

encapsulation of payload datagrams inside GPON encapsulation method (GEM) fragments. There is 

a wealth of other auxiliary features described in [ITU-T G.984.3], including the PLOAM channel, 

dynamic bandwidth allocation, and the PON-level QoS frameworks, that are possible. 

It should be noted that the DBA algorithm is not specified in any standard, but this is not an 

interoperability issue, and the non-specification has been intentional. 

The QoS system in GPON defines a scheme where each ONT may contain one or more 

transmission container(s) (T-CONTs). Each T-CONT may contain one or more GEM ports, which 

are the smallest connection that GPON systems handle. [ITU-T G.984.3] leaves the arrangement of 

T-CONT and GEM ports open. The mainstream arrangement is four service-bearing T-CONTs per 

ONT, with each representing a different class of service. 

[ITU-T G.984.4] defines the ONT management and configuration interface (OMCI). It defines both 

a management information base (MIB) for all the functions controlled in the ONT, as well as the 

ONT management communication channel (OMCC) that provides all the mechanisms required for 

the OLT to provide FCAPS functionality for the ONT. 

The OLT management is a somewhat more complex object. It contains by proxy all the MIBs of all 

the ONUs supported by that OLT, as well as all the other MIBs that describe the other functions in 

the OLT. This MIB is defined by several standards groups, including the Internet Engineering Task 

Force (IETF) and the TM forum. Typically, these MIBs are accessed using standard IETF-defined 

protocols (SNMP over TCP/IP). Most OLTs provide a dedicated Ethernet interface for this 

management traffic. 

All of the functions mentioned above are common functions, involved in all of the service traces 

that follow. They will be more compactly represented in the later diagrams for the sake of brevity. 

Case 6:20-cv-00534-ADA Document 47-14 Filed 03/05/21 Page 24 of 44
18 Rec. ITU-T G.984.1 (03/2008) 

TMF, 

IETF

PON Medium

G.984.3

G.984.2

PMD PMD

Eth. PMD TC TC

OMCC OMCC

G.984.4

TCP/IP

Eth. MAC

OLT MIB.

ONU MIB

802.3

SNMP

IETF

DBA QoS

Figure I.8 – GPON common functions 

The GPON real-time clock service is shown in Figure I.9. The OLT receives real-time clock data 

via NTP, typically over an Ethernet interface via UDP over IP. The OLT thereby maintains its own 

internal RTC, which it uses to timestamp all manner of event data. 

The ONT does not extend this RTC. Rather, its performance-monitoring and event-collection 

processes are synchronized with those of the OLT via the OMCI. The OLT routinely collects all of 

this data every 15 minutes and logs it with the OLT RTC. 

Case 6:20-cv-00534-ADA Document 47-14 Filed 03/05/21 Page 25 of 44
 Rec. ITU-T G.984.1 (03/2008) 19 

PON Medium

G.984.3

G.984.2

PMD PMD

Eth. PMD TC TC

OMCC

UDP/IP

Eth. MAC

OLT RTC

ONU MIB

802.3

NTP

IETF

OMCC

Figure I.9 – Real-time clock service 

The GPON network clock scheme is shown in Figure I.10. The OLT needs to obtain a high quality 

traceable timing clock, which serves as the master for all GPON interface timing. The normal 

source for the OLT's clock is a BITS timing input. However, in cases where a BITS source is not 

available, then an alternative method is needed. The alternative could be synchronous line timing 

from an SNI that is traceable to the network clock, or packet-based timing. 

Once the OLT network clock is established, it is used to source timing to the GPON interfaces, 

which in turn distribute timing to the counterpart ONT GPON interfaces. The ONT equipment then 

obtains its network clock from the GPON interface. This timing signal is ideal for TDM service 

interworking functions that are integrated into the ONT. Typically, this timing signal is not 

available to terminal adapters. However, if the timing signal is provided to the terminal adapters, 

then the synchronous Ethernet method is preferred. 

Case 6:20-cv-00534-ADA Document 47-14 Filed 03/05/21 Page 26 of 44
20 Rec. ITU-T G.984.1 (03/2008) 

PON Medium

G.984.3

G.984.2

PMD PMD

Eth. PMD TC TC

UDP/IP

Eth. MAC

OLT network clock

802.3

Pkt timing

IETF ONT 

Network clock

G.8261

DS-1

Phy

DS-1

framer

e.g., 

T1-107

BITS timing

Sync. timing

Figure I.10 – Network clock service 

I.3.2 Data functions 

The layer diagram for Ethernet service is shown in Figure I.11. In the ONT, Ethernet frames as 

defined in [b-IEEE 802.3] are extracted from the TC layer. In some ONTs, the Ethernet layer is 

quite abbreviated and little processing is done on the frames from their reception on the GPON 

interface to their transmission on the UNI. In other ONTs, true bridging is performed, with MAC 

address processing and potentially more. In some cases, PPPoE (not shown) is supported; however, 

this scheme seems to be waning. 

In some ONTs, some sort of VLAN processing is done, as defined in the IEEE 802.1-series of 

standards. Most systems use the 802.1ad version, where two layers of tags have been specified, 

although some systems actually support up to four layers of tags to be applied. This typically 

involves adding tag(s) in the upstream, and removing tag(s) in the downstream, for the purpose of 

identifying each user/service packet via their VLAN-ID. However, this is not necessary in all cases, 

since the PON itself has the GEM port-ID mechanism for such identification. 

On the OLT side, the Ethernet frames are taken from the GPON, and in some cases they receive 

their VLAN tags at the OLT (basically, swapping the GEM port-ID for an Ethernet VLAN tag). 

Then, in nearly all equipment, the resulting frames are switched using an Ethernet switching matrix. 

This switching can be on the basis of VLAN tags, or MAC addresses, or both. There are several 

mainstream arrangements of VLANs; these are specified in [b-DSL TR-101]. The traffic then 

leaves the OLT over some type of Ethernet interface, for connection to an edge routing device or 

other Ethernet aggregation device. 

It should be noted that there are several different interfaces that can take the place of an Ethernet 

Phy. These include xDSL (e.g., see below), MoCA, HPNA, HPNA-over-coax, 802.11 Wi-Fi, and 

perhaps others yet to be devised. However, due to Ethernet's pervasive nature, all of these 

alternative PHYs are defined so that they operate in a way nearly the same as Ethernet, and so their 

impact on the GPON system is rather small. 

All of these ONT features are controlled via the OMCI, as defined in [ITU-T G.984.4]. 

Case 6:20-cv-00534-ADA Document 47-14 Filed 03/05/21 Page 27 of 44
 Rec. ITU-T G.984.1 (03/2008) 21 

802.1 802.1

802.3

TR-101

Eth. PMD

G.984.4 (mgt)

Eth. MAC

VLAN switching

Eth. MAC Eth. MAC

Eth. PMD

Eth. MAC

802.3

VLAN tagging

PON Medium

G.984.3

G.984.2

PMD PMD

TC TC

IETF, TMF (mgt)

Figure I.11 – Ethernet data service 

The VDSL2 service is shown in Figure I.12. The first thing to be said is that the DSL type that is 

most widely used for GPON is VDSL2 (defined in the ITU-T G.993-x series of Recommendations), 

using packet transport mode. It is possible that ADSL2 plus or VDSL1 might be implemented for 

compatibility reasons, however, it is not the main thrust of most GPON development. With this 

said, the VDSL2 VTU-O function in the ONT operates much like an Ethernet PHY, and most of the 

layer diagram is similar to that of an Ethernet service. There are important differences, the biggest 

of which is the presence of multiple bearer channels in the same port. Each of these bearers would 

be treated as a 'virtual PHY', and the overall system is still unchanged. 

The management of the VTU-O located in the ONT is described in [ITU-T G.984.4]. 

802.1 802.1

802.3

TR-101

Eth. PMD

G.984.4 (mgt)

Eth. MAC

VLAN switching

Eth. MAC Eth. MAC

VDSL2

Eth. MAC 802.3

VLAN tagging

PON Medium

G.984.3

G.984.2

PMD PMD

TC TC

IETF, TMF (mgt)

G.993

Figure I.12 – VDSL2 service 

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22 Rec. ITU-T G.984.1 (03/2008) 

Figure I.13 describes the multicast service. This is really a logical service, usually provided in 

conjunction with an Ethernet UNI (or similar). However, it has an impact on the GPON system, so 

we include it here. The multicasting interactive signalling is provided by the IETF IGMP, versions 

2 or 3. This IP-layer multicasting topology is typically translated into Ethernet-layer multicasting 

via the trivial mapping defined in IEEE 802.1 standards. The management of multicasting, 

including the eligibility of UNIs to receive multicast traffic, the GPON ports that contain the 

multicast traffic, and their interconnection, is defined in [ITU-T G.984.4]. 

802.1 802.1

802.3

IGMPv2/3

Eth. PMD

G.984.4 (mgt)

Eth. MAC

Multicasting

Eth. MAC Eth. MAC

Eth. PMD

Eth. MAC

802.3

Multicasting

PON Medium

G.984.3

G.984.2

PMD PMD

TC TC

IETF, TMF (mgt)

Figure I.13 – Multicast service 

I.3.3 Voice functions 

The packet-based voice service flow is pictured in Figure I.14. By packet voice service, we describe 

a voice service that does not terminate on a class 5 TDM switch but instead is transported via an IP 

network to its destination. The mainstream protocol system used in this scenario is SIP, running 

over RTP/UDP/IP, all defined in IETF documents. This is easy to say, but because SIP-based VoIP 

aims to replace the class 5 switching system, it must therefore implement the sizable set of voice 

service features. A great deal of interoperability engineering must be done in any combination of 

VoIP-ONT and softswitch. 

The voice codecs are defined in the [b-ITU-T G.711], [b-ITU-T G.729], [b-ITU-T G.726], 

[b-ITU-T G.723] family. It should be noted that while the majority of VoIP systems are actively 

exploring advanced codecs for compression reasons, GPON is not concerned with this, since 

bandwidth is plentiful. In contrast, the codec selection here is mainly driven by interoperability with 

the far end of the SIP VoIP session. 

The POTS UNI is defined for the large part by national standards (e.g., European operators use 

[b-ETSI ETS 300 001]). However, it must be noted that POTS remains a very intricate service, and 

many operators have special requirements on the POTS interface, particularly on the lowest-level 

mechanical and electrical specifications of the metallic interface. 

From the SIP agent in the ONT, the service flow traverses a path very similar to the standard 

Ethernet service. VLAN tagging and Ethernet bridging may be applied at either the ONT, or OLT, 

or both. The user traffic, both bearer and signalling, leaves the OLT via an Ethernet interface, 

usually shared with other services. 

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 Rec. ITU-T G.984.1 (03/2008) 23 

The management of the packet voice service is varied at present. [ITU-T G.984.4] provides a full 

fault, configuration, accounting, performance-monitoring and security (FCAPS) support of SIP 

VoIP. However, there are several other in-band systems that are in use, such as TR-69, IETF 

sipping, and various proprietary configuration servers. These in-band systems are good in that they 

can manage VoIP terminal adapters anywhere on a network, so they have a wide reach. However, 

most suffer from poor practical standardization, and a lack of interactive features (such as the 

support of alarms and performance management). To help address this last point, even when an inband system is used for configuration of VoIP, the OMCI can still be used to gather alarms and PM 

information. This is basically a mixed management system. 

G.984.4 (mgt)

Eth. MAC

Cu

Phy

Codec

e.g., ETS 

300 001

VLAN

PON Medium

G.984.3

G.984.2

PMD

TC

802.3

G.711

Etc.

RTP/IP

IETF

TR-101

(mgt) TR-69

Sipping

Config Serv

POTS

802.3

Eth. PMD

Eth. MAC

VLAN switching

Eth. MAC

PMD

TC

IETF, TMF (mgt)

802.1

VoIP (SIP)

Figure I.14 – Packet voice service 

The protocol stack diagram for circuit-switched voice service is shown in Figure I.15. In this 

scenario, VoIP is being used to transport the voice signals from the ONT to the class 5 TDM switch 

in the central office, and no further. The protocol used in this case is usually H.248, since this 

system is suited to voice gateway interfaces, of which the ONT and OLT each have one. 

At the ONT, from the codec and below, the arrangement is exactly the same as in the packet voice 

case. 

At the OLT, the H.248 flow is terminated, usually in a special-purpose voice gateway module. This 

module's function is to regenerate the customer's voice interface, and format the data representing 

that interface in the way that a conventional DLC system would, as defined by the appropriate 

regional standard (e.g., V5.2). This interface, most commonly carried physically by DS1 or E1 

interfaces, can then be tied directly into a class 5 switch with integrated DLC interfaces. The whole 

intent is to minimize the impact of the GPON deployment on the normal operation of voice services 

in the CO. 

The management of this kind of VoIP also has the potential for standard overlap, since all the 

options are available for H.248 ONTs. However, the OMCI method is used quite often in this case, 

since the advantages of the in-band system all but disappear for this scenario. The OMCI is a 

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24 Rec. ITU-T G.984.1 (03/2008) 

self-contained solution for the management of voice services on GPON, and seems an easy choice 

in this scenario. 

There are additional combinations of transport protocols, functional architectures and management 

protocols that are possible. The intent of the two illustrations here is to highlight the most active 

combinations. 

TR-101

802.1

DS-1

G.984.4 (mgt)

GR-303

VLAN

Eth. MAC Eth. MAC

Cu

Phy

Codec

e.g., ETS 

300 001

VLAN

PON Medium

G.984.3

G.984.2

PMD PMD

TC TC

802.3

G.711

Etc.

RTP/IP RTP/IP

VoIP

Codec G.711

Etc.

e.g.,

V5.2

IETF

IETF, TMF (mgt)

POTS

H.248 VoIP

Figure I.15 – Circuit-switched voice service 

I.3.4 Circuit emulation functions 

TDM interfaces can also be supported over packet transport on GPON, as shown in Figures I.16 and 

I.17 (note the DS-01/E1 Framer would not be required for a transparent T1/E1 service). There are 

several options that can be exercised here. The first involves the transport of the actual TDM 

payload, using either a variant of the IETF PWE3 system of protocols (shown above), or the Metro 

Ethernet forum's MEF 8 protocol. The second involves the use of a local OLT TDM interface 

(shown above) or the use of a packet interface on the OLT leading to a gateway somewhere else in 

the network. This would seem to present quite a large set of alternatives, but in practice it has turned 

out not to be a big issue because most hardware supports nearly all of the options. So, 

interoperability is mostly a matter of negotiating the transport protocol. Circuit emulation may also 

require a network clock to be delivered to the PWE3 interworking functions. Differential timing 

mode supports better jitter/wander performance than adaptive mode. 

The GPON core, up to and including the VLAN layer is the same as in the typical Ethernet service. 

The actual TDM interfaces are defined in, for example, [b-ITU-T G.703] for DS1 and E1 interfaces, 

or the appropriate regional standard (e.g., [b-ATIS T1-107] for DS1 interfaces, [b-ETSI ETS 300 

166] for E1 interfaces). 

The management of either PWE3 or MEF 8 interworking is described in [ITU-T G.984.4]. 

Case 6:20-cv-00534-ADA Document 47-14 Filed 03/05/21 Page 31 of 44
 Rec. ITU-T G.984.1 (03/2008) 25 

TR-101

802.1

DS-1

Phy

G.984.4 (mgt)

DS-1

framer

VLAN

Eth. MAC Eth. MAC

DS-1

Phy

e.g., 

T1-107

VLAN

PON Medium

G.984.3

G.984.2

PMD PMD

TC TC

802.3

RTP/IP

PWE3

RTP/IP

PWE3

e.g.,

T1-107

IETF, TMF (mgt)

DS-1

framer

IETF

Figure I.16 – Packet TDM service using PWE3 and grooming OLT 

TR-101

802.1

G.984.4 (mgt)

VLAN

Eth. MAC Eth. MAC

E1

Phy

e.g., ETS

300 166

VLAN

PON Medium

G.984.3

G.984.2

PMD PMD

TC TC

802.3

MEF-8

IETF, TMF (mgt)

E1

framer

MEF

802.3

Eth. PMD

Eth. MAC

Figure I.17 – Packet TDM service using MEF 8 and pure OLT 

Case 6:20-cv-00534-ADA Document 47-14 Filed 03/05/21 Page 32 of 44
26 Rec. ITU-T G.984.1 (03/2008) 

Figure I.18 shows an alternative for TDM service transport within the GPON system. This scheme 

transports SDH tributary units over GEM ports directly. The definition of the format of the 

encapsulated data is defined in [b-ITU-T G.707]. This scheme is mainly applicable where the TDM 

service will be terminated at the OLT and transported in an SDH interface, as shown. 

The management of this method at the ONT is through the OMCI ([ITU-T G.984.4]). 

SDH

Phy

G.984.4 (mgt)

SDH

framer

DS-1

Phy

e.g., 

T1-107

PON Medium

G.984.3

G.984.2

PMD PMD

TC TC

SDH SDH

G.957

IETF, TMF (mgt)

DS-1

framer

G.707

G.707

Figure I.18 – Circuit TDM service 

I.3.5 Video overlay functions 

Figure I.19 shows the video overlay service. This is carried on the PON using a third wavelength, 

and is practically distinct from the other services. The signal format delivered to the customer is 

defined by SCTE standards, and the management of the ONT interface is given by 

[ITU-T G.984.4]. The optical interfaces throughout the rest of the service path are generally defined 

by [b-ITU-T J.186]. In practice, the details of the video OLT and subtending optical amplifiers are 

left to network operator engineering, especially the signal levels at each point in the network. This 

is due to the large variations in network physical topology and channel plans. 

G.984.4 (mgt)

PON Medium

PMD

SCTE (mgt)

EDFA

Tx

SCTE-40

J.186

Figure I.19 – Video overlay service 

Case 6:20-cv-00534-ADA Document 47-14 Filed 03/05/21 Page 33 of 44
 Rec. ITU-T G.984.1 (03/2008) 27 

Appendix II 

External access network backup 

(This appendix does not form an integral part of this Recommendation) 

In many applications, some resilience to faults in the optical access network is desired, but the cost 

of full protection as described in clause 14 is not supportable. In these cases, a cost-effective 

alternative is to provide a lower capacity backup to the service via an external access network. 

Examples of the external access network include digital subscriber line, fixed wireless, mobile 

wireless, or hybrid fibre-coax networks. 

Because of the wide range of backup access networks, the interface from the PON equipment to the 

backup network has to be at the data frame networking layer, described in the IEEE 802.1 

standards. By abstracting the interface to this layer, the PON equipment need not worry about the 

details of the backup network (nor does the backup network need to worry about the PON). 

The key aspect of such external backup is the location and control of the backup switching logic. 

Because of the widely disparate capacities of the primary PON and the backup network, it does not 

make sense to send two copies of traffic at all times. Also, due to the packet-nature of the traffic, it 

is difficult for the receiver to resolve multiple copies of the same packets. It is assumed that the 

receiver will simply accept all packets arriving from either access network; therefore, it is important 

to only send one copy of any packet. Therefore, the source side must direct the traffic to the 

appropriate access network, and it must have the information required to make the correct choice. In 

addition, the source side switching equipment must also have the ability to prioritize traffic and 

selectively discard traffic that exceeds the capacity of the backup network when backup is in force. 

In the upstream, the backup switch can be located in the ONU or beyond the UNI. In the 

downstream direction, the backup switch can be located in the OLT or beyond the SNI. These 

arrangements are illustrated in Figure II.1. 

Case 6:20-cv-00534-ADA Document 47-14 Filed 03/05/21 Page 34 of 44
28 Rec. ITU-T G.984.1 (03/2008) 

Back

Up

Sw.

PON LT

AN I/F 

ODN UNI LT

External 

AN

Back

Up

Sw.

SNI LT

AN I/F 

PON LT

ONU OLT

SNI LT

Service

Node

User

Equip.

ODN

External 

AN

Back

Up

Sw.

SNI LT

AN I/F 

PON LT

OLT

SNI LT

Service

Node

Back

Up

Sw.

PON LT

AN I/F 

ODN UNI LT

External 

AN

ONU

User

Equip.

PON LT ODN UNI LT

External 

AN

Back

Up

Sw.

PON LT SNI LT

ONU OLT

Service

Node

User

Equip.

Back

Up

Sw.

Back

Up

Sw.

PON LT SNI LT

OLT

Service

Node

UNI LT PON LT

ONU

User

Equip.

Back

Up

Sw.

(a)

(b)

(c)

(d)

Figure II.1 – The four switching arrangements for external access network backup 

In option a), the switches are both located in the PON equipment. It is assumed that the PON 

equipment has knowledge of the PON link's operational state, and therefore it can direct traffic to 

the PON interface if it is working correctly and to the backup network interface if it is not. 

Therefore, no additional signalling is required. The configuration of the ONU's dual ANIs must be 

supported in the OMCI. 

In option b), the upstream switch is located beyond the ONT's UNI. A typical situation would be for 

this function to be located in an Ethernet switch or IP router. Therefore, that switch must be capable 

of learning the status of the ONU's PON link via some form of signalling. This could be as crude as 

the ONU deactivating the UNI when the PON link has failed, to some more sophisticated Ethernet 

alarm indication signal (AIS) such as described in [b-ITU-T Y.1731]. The downstream switch is 

internally controlled within the OLT. 

In option c), the downstream switch is located beyond the OLT's SNI. A typical function would be 

for this function to be located in an Ethernet aggregation network or service edge router. Just as in 

option b), this switching logic must be given the information on the status of the PON link to the 

ONT in question. Unlike the previous case, however, a sophisticated per-ONT AIS scheme must be 

employed since the SNI is shared over many ONUs, some of which may not have a PON 

transmission problem. This could be the AIS as described in [b-ITU-T Y.1731], but applied on a 

per-VLAN basis. The upstream switch is internally controlled within the ONU, with the 

configuration of the ONU's dual ANIs being supported in the OMCI. 

Case 6:20-cv-00534-ADA Document 47-14 Filed 03/05/21 Page 35 of 44
 Rec. ITU-T G.984.1 (03/2008) 29 

In option d), both of the switches are located beyond the PON equipment. This scheme is most 

distantly removed from the access networks, since all the backup switching/routing is happening in 

other equipment. This raises the possibility of allowing the backup to occur using the more 

autonomous schemes such as Ethernet spanning tree or IP routing. In either case, the backup link 

would need to be configured as the 'expensive link', so that it would not be used if the PON link was 

available. These Layer 2 or 3 schemes tend to take longer than more direct schemes mentioned in 

the previous options a-c. Their performance could be improved by implementing the direct AIS 

schemes to provide a faster feedback into their control algorithms. 

Case 6:20-cv-00534-ADA Document 47-14 Filed 03/05/21 Page 36 of 44
30 Rec. ITU-T G.984.1 (03/2008) 

Appendix III 

Dual-parenting resilience 

(This appendix does not form an integral part of this Recommendation) 

Dual-parenting resilience refers to a system where PON protection is implemented using two OLT 

line terminations that are provided in two separate OLT equipment, typically in physically diverse 

locations. Such a scheme offers protection from catastrophic failure of the OLT equipment, its 

power supply, and the physical locality where it is placed. 

Unlike traditional PON protection, where both PON sections terminated in the same equipment, 

dual parenting requires coordination of the functions of two PONs in separate equipment. The 

prerequisite to accomplish this is that the ONUs being protected must be registered on both the 

working and remote OLTs. In this way, the logical state of the working OLT can be reproduced in 

the protection OLT with a minimum of delay. In addition, the protection switching of traffic 

upstream from both OLTs must also be supported. This topic is for future study, and is out of the 

scope of this discussion. 

In dual-parenting type B protection, shown in Figure III.1, the main functionality to implement 

resilience resides within the OLT. This scheme requires the protection OLT to be in standby state, 

therefore it is necessary to synchronize the operation status of both OLTs. Additionally, a data 

communications channel is necessary between the two OLTs for sharing the service configuration 

of all ONUs that is needed to re-establish the connections between all UNIs and SNIs at the remote 

OLT (Figure III.1). 

PON LT (1)

OLT

ONU #1

PON LT (0)

OLT

Inter OLT 

communications 

channel

ODN

ONU #N

PON LT (1)

OLT

ONU #1

PON LT (0)

OLT

Inter OLT 

communications 

channel

ODN

ONU #N

Figure III.1 – Diagram showing a communications channel between 

working and remote standby OLTs 

The data communications channel between the two OLTs can be implemented in different ways. 

One straightforward method is using the management plane at either the element management layer 

or network management layer (Figure III.2). 

Case 6:20-cv-00534-ADA Document 47-14 Filed 03/05/21 Page 37 of 44
 Rec. ITU-T G.984.1 (03/2008) 31 

PON LT (1)

OLT

PON LT (0)

OLT

TMN

Q3

Q3 ODN

ONU #1

ONU #N

PON LT (1)

OLT

PON LT (0)

OLT

TMN

Q3

Q3 ODN

ONU #1

ONU #N

Figure III.2 – Inter-OLT communications channel established through management plane 

The events that trigger dual-parenting switching are: 

1) Fibre cut in the ODN on the working OLT side. 

2) Degraded link. 

3) Failure of the PON LT in the OLT. 

4) OLT failure. 

The standby remote OLT could be triggered (enabled) after asserting PON LT LOS and a second 

check via inter-OLT communications channel. A dying gasp message from all ONUs should 

prevent dual-parenting switch-over. 

The remote standby OLT should maintain, as a minimum, the serial number list of registered ONUs 

and the service profile of each ONU. Optionally, other data are also possible to be shared between 

working and remote OLT in order to speed up service recovery. 

Case 6:20-cv-00534-ADA Document 47-14 Filed 03/05/21 Page 38 of 44
32 Rec. ITU-T G.984.1 (03/2008) 

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Printed in Switzerland 

Geneva, 2009 

SERIES OF ITU-T RECOMMENDATIONS 

Series A Organization of the work of ITU-T 

Series D General tariff principles 

Series E Overall network operation, telephone service, service operation and human factors 

Series F Non-telephone telecommunication services 

Series G Transmission systems and media, digital systems and networks 

Series H Audiovisual and multimedia systems 

Series I Integrated services digital network 

Series J Cable networks and transmission of television, sound programme and other multimedia signals 

Series K Protection against interference 

Series L Construction, installation and protection of cables and other elements of outside plant 

Series M Telecommunication management, including TMN and network maintenance 

Series N Maintenance: international sound programme and television transmission circuits 

Series O Specifications of measuring equipment 

Series P Telephone transmission quality, telephone installations, local line networks 

Series Q Switching and signalling 

Series R Telegraph transmission 

Series S Telegraph services terminal equipment 

Series T Terminals for telematic services 

Series U Telegraph switching 

Series V Data communication over the telephone network 

Series X Data networks, open system communications and security 

Series Y Global information infrastructure, Internet protocol aspects and next-generation networks 

Series Z Languages and general software aspects for telecommunication systems 

 

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