XGS-PON Technical White

Paper
 XGS-PON Technical White Paper

TABLE OF CONTENTS

1 Executive Summary....................................................................................................... 5

2 Abbreviations and Acronyms......................................................................................5

3 XGS-PON Standards...................................................................................................... 6

4 XGS-PON Application Scenarios................................................................................ 7

5 XGS-PON PMD Layer..................................................................................................... 9

5.1 Classes for Optical Path Loss..........................................................................................9
5.2 Line Rate............................................................................................................................. 9
5.3 Line Code............................................................................................................................9
5.4 Wavelength Allocations.....................................................................................................9
5.5 XGS-PON Compatible ODN.......................................................................................... 10
5.6 Optical Interface Parameters of 9.95328 Gbit/s Downstream Direction................. 10
5.7 Optical Interface Parameters of 9.95328 Gbit/s Upstream Direction...................... 12

6 XGS-PON Transmission Convergence Layer....................................................... 14

6.1 Time Division Multiplexing Architecture....................................................................... 14
6.2 Media Access Control..................................................................................................... 15
6.3 Ranging............................................................................................................................. 16
6.4 DBA....................................................................................................................................17
6.5 Downstream XGS TC Framing......................................................................................18
6.6 Upstream XGS TC Framing...........................................................................................21
6.7 XGEM Framing................................................................................................................ 22
6.8 PLOAM Messaging Channel......................................................................................... 23
6.9 ONU Activation.................................................................................................................24
6.10 Security............................................................................................................................. 25
6.10.1 Authentication...................................................................................................................25
6.10.2 XGEM Payload Encryption.............................................................................................25
6.10.3 Message Integrity Check................................................................................................25
6.11 Power Saving................................................................................................................... 25
6.12 Protection Switchover..................................................................................................... 26

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7 ONU Management and Control Interface (OMCI)................................................. 27

7.1 Configuration Management............................................................................................29
7.2 Fault Management...........................................................................................................29
7.3 Performance Management.............................................................................................30
7.4 Security Management..................................................................................................... 30
7.5 ONU Management and Control Protocol..................................................................... 30

8 Technical Differences among GPON, XG-ON and XGS-PON............................32

9 Migration towards XGS-PON..................................................................................... 33

9.1 Compatibility between XG-PON and XGS-PON.........................................................33
9.2 Coexistence between XGS-PON and GPON through WDM1r................................ 34

10 Conclusions................................................................................................................... 35

11 References......................................................................................................................35

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IGURES

Figure 4-1 XGS-PON Application Scenarios (Excerpted from G.9807)..................................... 8

Figure 5-1 Wavelength Allocations for XGS-PON, GPON and RF Video................................10

Figure 6-1 Downstream Multiplexing in XGS-PON......................................................................14

Figure 6-2 Upstream Multiplexing in XGS-PON...........................................................................15

Figure 6-3 XGS TC Media Access Control Concept................................................................... 16

Figure 6-4 Ranging Mechanism......................................................................................................17

Figure 6-5 DBA Abstraction.............................................................................................................18

Figure 6-6 Downstream XGS TC Frame and Its Header............................................................19

Figure 6-7 BWmap Partition and the Format of an Allocation Structure.................................. 19

Figure 6-8 Downstream PLOAM Partition.....................................................................................20

Figure 6-9 Downstream PHY Frame..............................................................................................20

Figure 6-10 Upstream XGS TC Burst Header and Trailerframe Overhead Fields.................21

Figure 6-11 Upstream PHY Frame................................................................................................ 22

Figure 6-12 The Structure of XGS TC Payload............................................................................22

Figure 6-13 XGEM Header Format................................................................................................ 23

Figure 7-1 Reference model, OMCI...............................................................................................27

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Figure 7-2 ONU functional block diagram.....................................................................................28

Figure 9-1 Compatibility between XG-PON and XGS-PON.......................................................33

Figure 9-2 Coexistence between XGS-PON and GPON through WDM1r.............................. 34

TABLES

Table 5-1 Classes for Optical Path Loss......................................................................................... 9

Table 5-2 Physical Parameters of a Simple ODN (ODS)........................................................... 10

Table 5-3 Optical Interface Parameters of 9.95328 Gbit/s Downstream Direction................ 11

Table 5-4 Optical Interface Parameters of 9.95328 Gbit/s Upstream Direction......................12

Table 7-1 Baseline OMCI Message Format................................................................................. 31

Table 7-2 Extended OMCI Message Format................................................................................32

Table 8-1 Technical Differences among GPON, XG-ON and XGS-PON................................ 32

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 XGS-PON Technical White Paper

1 Executive Summary
This technical white paper introduces the requirements, physical layer, transmission
convergence layer and OMCI of XGS-PON.

2 Abbreviations and Acronyms

Alloc-ID Allocation identifier

BWmap Bandwidth map

CATV Community Antenna Television

CBU Cell-site backhauling unit

DBA Dynamic bandwidth assignment

DBRu Upstream dynamic bandwidth assignment report

FTTx Fiber to (B – building; H: home; C: optical cross connect cabinet, Cell: cell site)

FEC Forward error correction

G-PON Gigabyte Passive Optical Network

MDU Multiple dwelling unit

MTU Multi-tenant unit

NRZ Non-Return to Zero

OAM Operations, administration and management

ODN Optical Distribution Network

OLT Optical line terminal

OMCI ONU management and control interface

ONT Optical network terminal

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XGS-PON Technical White Paper

ONU Optical network unit

PLOAM Physical layer operations, administration and maintenance

PMD Physical medium dependent (protocol layer)

PSBd Downstream physical synchronization block

PSBu Upstream physical synchronization block

PSync Physical synchronization sequence

RE Reach extender

RF-Video Frequency-Video

SBU Small business unit

SFU Single family unit

TC Transmission convergence

T-CONT Transmission container

WDM1r Wavelength division multiplexor 1 revised (coexistence device)

XGEM XGS-PON Encapsulation Method

XGS-PON 10-Gigabit-capable passive optical network, G.987 series

XGTC XG-PON Transmission Convergence

XGS TC XGS-PON Transmission Convergence

3 XGS-PON Standards
XG-PON is the next-generation evolution of the GPON technology. It was originally
divided into two stages, the XG-PON1 (10G/2.5G) and XG-PON2 (10G/10G). However,
only the XG-PON1 standard was formulated. The XGS-PON standard G.9807.1

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10-Gigabit-capable symmetric passive optical network was released in June 2016.

XG-PON refers to 10G/2.5G PON and XGS-PON refers to 10G/10G PON.

Different from other ITU-T PON standards, the XGS-PON standards was defined in
G.9807.1 Annex.

 G.9807.1 10-Gigabit-capable symmetric passive optical network (XGS-PON)

Definitions, abbreviations, and acronyms.

 G.9807.1 Annex A:

General requirements of XGS-PON.

 G.9807.1 Annex B

Physical media dependent (PMD) layer specifications of XGS-PON

 G.9807.1 Annex C

Transmission convergence layer specifications of XGS-PON

 G.988

ONU management and control interface (OMCI) specification

4 XGS-PON Application Scenarios

XGS-PON is the next-generation evolution of GPON; therefore the XGS-PON scenarios
are similar with the GPON scenarios. XGS-PON application scenarios can be divided
into three parts: the cell station users, the business users and the residential users.

The cell station user scenarios is FTTCell. The type of the ONUs used in the FTTCell
scenario is called Cellular Backhaul Unit (CBU), which supports base station backhaul.
CBU needs to support IEEE1588 and Synchronous Ethernet.

The commercial user scenarios include FTTB and FTTO. The types of the ONUs used in
the commercial user scenarios are MTU and SBU, which support commercial data

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transfer, E1 services, commercial video conferencing, and commercial voice

conferencing.

The residential user scenarios inculde FTTH, FTTdp, FTTB and FTTC. The types of the
ONUs used in the residentail user scenarios are SFU and LAN based MDU as well as
the DSL and G.fast based MDU, which provide high-speed Internet services, voice
services and video services.

Figure 4-1 XGS-PON Application Scenarios (Excerpted from G.9807)

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5 XGS-PON PMD Layer

5.1 Classes for Optical Path Loss

Table 5-1 Classes for Optical Path Loss

‘Nominal1’ ‘Nominal2’ ’Extended1’ “Extended2”

class class class class
(N1 class) (N2 class) (E1 class) (E2 class)

Minimum 14 dB 16 dB 18 dB 20 dB
loss

Maximum 29 dB 31 dB 33 dB 35 dB
loss

5.2 Line Rate

The line rates of XGS-PON are defined as 9.95328 Gbit/s in the downstream direction
and 9.95328 Gbit/s in the upstream direction.

5.3 Line Code

The downstream and upstream line code of XGS-PON is non-return to zero (NRZ) code.

5.4 Wavelength Allocations

The wavelengths of XGS-PON are specified as 1575-1580 nm in the downstream and

1260-1280 nm in the upstream direction, which are the same as that of XG-PON.

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Figure 5-1 Wavelength Allocations for XGS-PON, GPON and RF Video

5.5 XGS-PON Compatible ODN

Table 5-2 Physical Parameters of a Simple ODN (ODS)

Item Unit Specification

Fibre type – [ITU-T G.652], or compatible

N1 class: 14 – 29
N2 class: 16 – 31
Attenuation range dB
E1 class: 18 –33
E2 class: 20 –- 35

Maximum fibre distance between

km DD20: 20
S/R and R/S points

Minimum fibre distance between

km 0
S/R and R/S points

Bidirectional transmission – 1-fibre WDM

Maintenance wavelength nm See [ITU-T L.66]

5.6 Optical Interface Parameters of 9.95328 Gbit/s

Downstream Direction

All of the following parameters are applicable to the optical interfaces with a maximum
differential distance of 20 km. The parameters of the optical interfaces with a maximum
differentiated distance of 40 km need to be defined.

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Table 5-3 Optical Interface Parameters of 9.95328 Gbit/s Downstream Direction

Item Unit Value

OLT transmitter (optical interface Old)

Nominal line rate Gbit/ 9.95328

s

Operating wavelength nm 1575 – 1580

Line code – NRZ

Mask of the transmitter eye – see ITU-T G.9807.1

diagram

Maximum reflectance at S/R, dB NA

measured at transmitter
wavelength

Minimum ORL of ODN at Olu and dB more than 32

Old

ODN Class N1 N2 E1 E2

Mean launched power MIN dBm +2.0 +4.0 +6 FFS

Mean launched power MAX dBm +5.0 +7.0 +9 FFS

Launched optical power without dBm NA

input to the transmitter

Minimum extinction ratio dB 8.2

Tolerance to the transmitter dB more than -15

incident light power

Dispersion Range ps/n 0-400

m

Minimum side mode suppression dB 30

ratio

Maximum Optical Path Penalty at dB 1.0

20km

Maximum Differential optical path

dB 15
loss

ONU receiver (optical interface Ord)

Maximum reflectance at R/S, dB less than -20

measured at receiver wavelength

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Item Unit Value

Bit Error Ratio reference level – 10-3

ODN Class N1 N2 E1 E2

Minimum sensitivity at BER dB -28.0 -28.0 -28.0 FFS

reference level m

Minimum overload at BER dB -9.0 -9.0 -9.0 FFS

reference level m

Consecutive identical digit bit more than 72

immunity

Jitter tolerance – see ITU-T G.9807.1

Tolerance to reflected optical dB less than 10

power

5.7 Optical Interface Parameters of 9.95328 Gbit/s

Upstream Direction

Table 5-4 Optical Interface Parameters of 9.95328 Gbit/s Upstream Direction

Item Unit Value

ONU transmitter (optical interface Oru)

Nominal line rate Gbit/ 9.95328

s

Operating wavelength nm 1260 – 1280

Line code – NRZ

Mask of the transmitter eye diagram – see ITU-T G.9807.1

Maximum reflectance at R/S, dB -10

measured at transmitter wavelength

Minimum ORL of ODN at Oru and Ord dB more than 32

ODN Class N1 N2 E1 E2

Mean launched power MIN dBm +4.0 +4.0 +4.0 FFS

Mean launched power MAX dBm +9.0 +9.0 +9.0 FFS

Launched optical power without input dBm -45

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Item Unit Value

to the transmitter

Maximum Tx Enable bits 1280

Maximum Tx Disable bits 1280

Minimum extinction ratio dB 6.0

Tolerance to reflected optical power dB more than -15

Dispersion Range ps/n 0 to -140

m

Minimum side mode suppression dB 30

ratio

Jitter transfer – see ITU-T G.9807.1

Jitter generation – see ITU-T G.9807.1

Maximum Optical Path Penalty at 20 dB 1.0

km

OLT receiver (optical interface Olu)

Maximum reflectance at S/R, dB -12

measured at receiver wavelength

Bit Error Ratio reference level – 10-3

ODN Class N1 N2 E1 E2

Minimum sensitivity at BER reference

dBm -26.0 -28.0 -30.0 FFS
level

Minimum overload at BER reference dBm -5.0 -7.0 -9.0 FFS

level

Consecutive identical digit immunity Bbit more than 72

Jitter tolerance – see ITU-T G.9807.1

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6 XGS-PON Transmission Convergence

Layer

6.1 Time Division Multiplexing Architecture

In the downstream direction, the OLT multiplexes the XGEM frames onto the
transmission medium using XGEM Port-ID as a key to identify the XGEM frames that
belong to different downstream logical connections. Multicast XGEM Port-IDs can be
used to carry XGEM frames to more than one ONU. Multiplexing in the downstream is

illustrated in Figure 6-1.

Figure 6-1 Downstream Multiplexing in XGS-PON

In the upstream direction, the OLT first grants bandwidth allocations to Alloc-IDs within
the subtending ONUs based on DBA function. The bandwidth allocations to different
Alloc-IDs are multiplexed in time as specified by the OLT in the bandwidth maps
transmitted downstream. Within each bandwidth allocation, the ONU uses the XGEM
Port-ID as a multiplexing key to identify the XGEM frames that belong to different
upstream logical connections. The multiplexing in the upstream is illustrated in Figure

6-2.

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Figure 6-2 Upstream Multiplexing in XGS-PON

6.2 Media Access Control

The OLT transmits a downstream PHY frame every 125s. Because of the varying fibre
distance, each given PHY frame reaches different ONUs at generally different moments
of time. With each received downstream PHY frame, an ONU associates the
corresponding upstream PHY frame. The individual equalization delays established in
the course of ONU ranging serve to align the ONU views on the start of each upstream
PHY frame in such a way, that upstream transmissions by any ONU occurring at fixed
offset with the upstream PHY frame would reach the OLT at precisely the same time
instant.

For each PHY frame, the OLT creates and transmits downstream a BWmap that
specifies a sequence of non-overlapping upstream transmissions by different ONUs. A
BWmap contains a number of allocation structures, each allocation structure being
addressed to a particular Alloc-ID of a specific ONU. A sequence of one or more
allocation structures addressed to Alloc-IDs that belong to the same ONU form a burst
allocation series. Each burst allocation series contains a start pointer indicating the
beginning of the burst within the upstream PHY frame and a sequence of grant sizes that
the ONU is allowed to transmit. The start pointers refer to offsets within the upstream
PHY frame, whereas the grant sizes pertain to the payload of XGTC frame. The start

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pointers and grant sizes are expressed in units of words (one word equals 4 bytes). The
OLT may grant higher or lower effective data rates by controlling the size and frequency
of the grants and may modulate the effective data rate via dynamic scheduling.

The media access control concept in an XGS-PON system is illustrated in Figure 6-3.

Figure 6-3 XGS TC Media Access Control Concept

6.3 Ranging

The XGS-PON system leverages a P2MP architecture. Multiple ONUs are connected to
one OLT and have different physical distances between the OLT. Upstream
transmissions from ONUs with different physical distances between the OLT can
potentially conflict with each other, even if the ONUs transmit in their own bandwidth
allocations.

Ranging is a function to measure the logical distance between each ONU and OLT, and
to adjust the logical distance to a unique one. Thus, the adjusted logical distances of all
ONUs are unique and upstream transmissions from different ONUs in different
bandwidth allocations will not conflict.

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Figure 6-4 illustrates the basic ranging mechanism. An equalization delay is assigned to

ONUi. When receiving bandwidth allocation, ONUi always delays the duration of
equalization delay before transmitting in the upstream bandwidth. From the OLT’s view,
the logical distance between ONUi and OLT is the same as that between the farthest
ONU and the OLT.

Figure 6-4 Ranging Mechanism

6.4 DBA

DBA in XGS-PON is the process in which the OLT allocates upstream transmission

opportunities to the traffic-bearing entities within ONUs, as shown in Figure 6-5, based on

dynamic indication of their activity and their configured traffic contracts. The activity
status indication can be either explicit through buffer status reporting, or implicit through
transmission of idle XGEM frames in place of upstream transmission opportunities.

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Figure 6-5 DBA Abstraction

6.5 Downstream XGS TC Framing

The downstream XGS TC frame has the fixed size of 135432 bytes and consists of the

XGS TC header, the XGS TC payload, and the trailer, as shown in Figure 6-6.

The downstream XGS TC frame header consists of a fixed size HLend structure and two
variable size partitions: the Bandwidth map partition (BWmap) and downstream PLOAM
partition (PLOAMd).

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Figure 6-6 Downstream XGS TC Frame and Its Header

The BWmap is a series of 8-byte allocation structures. The number of allocation

structures in the BWmap is given in the BWmap length field of the HLend structure. The
actual length of the BWmap partition is 8*N bytes.

Each allocation structure specifies a bandwidth allocation to a particular Alloc-ID, the

position and size of the bandwidth by StartTime and GrantSize and operational options
including DBRu, PLOAMu, FWI, BProfile. The formats of the BWmap partition and an

allocation structure are shown in Figure 6-7.

Figure 6-7 BWmap Partition and the Format of an Allocation Structure

The PLOAMd partition contains zero, one or more PLOAM messages. The length of
each PLOAM message is 48 bytes. The number of PLOAM messages in the PLOAMd

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partition is given by the PLOAM Count field of the HLend structure. The actual length of
the PLOAMd partition is 48*P bytes.

Figure 6-8 Downstream PLOAM Partition

The size of a downstream PHY frame is 155520 bytes (38880 words). A diagram of the

downstream PHY frame structure is shown in Figure 6-9. Based on the downstream XGS

TC frame, PSBd and FEC parities are inserted accordingly. The PSBd field is 24-bytes
long and contains an 8-bytes Physical Synchronization, an 8-bytes Superframe Counter
and an 8-bytes operation control code.

Figure 6-9 Downstream PHY Frame

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6.6 Upstream XGS TC Framing

In the upstream direction, PDU of the Framing sublayer is represented by an upstream

XGS TC burst. The upstream XGS TC burst transmitted by a given ONU has a
dynamically determined size and consists of the upstream XGS TC burst header, one or
more bandwidth allocation intervals, each being associated with a specific Alloc-ID, and

the XGS TC trailer, as shown in Figure 6-10.

Figure 6-10 Upstream XGS TC Burst Header and Trailerframe Overhead Fields

The size of an upstream PHY frame is 155,520 bytes (38,880 words).

The relationship between PHY framing boundaries and the upstream PHY bursts of

different ONUs is illustrated in Figure 6-11. Based on the upstream XGS TC frame, PSBu

and FEC parities are inserted. The PSBu contains a Preamble and Deilimiter fields. In
the upstream RS(248, 232), truncated RS(255, 239) FEC code is used.

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Figure 6-11 Upstream PHY Frame

6.7 XGEM Framing

The XGS TC payload, as shown in Figure 6-6 and Figure 6-10, contains one or more

XGEM frames (see Figure 6-12).

Figure 6-12 The Structure of XGS TC Payload

Each XGEM frame contains a fixed size XGEM header and a variable size XGEM
payload field.

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The size of the XGEM header is 8 bytes. The format of the XGEM header is shown in

Figure 6-13, including Payload Length Indication (PLI) and Key Index.

Figure 6-13 XGEM Header Format

6.8 PLOAM Messaging Channel

The physical layer OAM (PLOAM) messaging channel in an XGS-PON system is an

operations and management facility between OLT and ONUs that is based on a fixed set
of messages transported within a designated field of the XGS TC frame header
(downstream) and the XGS TC burst header (upstream). The PLOAM channel provides
more flexible functionality than the embedded management channel and is generally
faster than the OMCI channel.

The PLOAM channel supports XGS-PON TC layer management functions. It is based

upon exchange of 48-byte messages that are transported in the PLOAM partition of the
downstream XGS TC frame header and in the upstream XGS TC burst header.

The physical layer OAM (PLOAM) channel supports the following functions:

 Burst profile communication;

 ONU activation;

 ONU registration;

 Encryption key update exchange;

 Protection switching signaling;

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 Power management.

6.9 ONU Activation

The outline of activation process events in their causal order is given below:

 The ONU entering the activation process listens to the downstream transmission
and attains PSync and superframe synchronization. At that time the ONU learns
PON-ID.

 The ONU listens to the Profile PLOAM messages, periodically issued by the OLT, to
start learning the burst profiles specified for the upstream transmission.

 Once the ONU receives a serial number grant with a known profile, it announces its
presence on the PON with a Serial_Number_ONU PLOAM message.

 The OLT discovers the serial number of a newly connected ONU and assigns an
ONU-ID to it using the Assign_ONU-ID message.

 The OLT issues a directed ranging grant to a newly discovered ONU and prepares
to accurately time the response time.

 The ONU responds with the Registration PLOAM message.

 The OLT performs initial authentication of the ONU based on the Registration ID,
computes the individual equalization delay and communicates this equalization
delay to the ONU using the Ranging_Time PLOAM message.

 The ONU adjusts the start of its upstream XGS TC frame clock based on its
assigned equalization delay.

 OLT optionally performs the strong bidirectional authentication procedure by one of

the available methods.

 The ONU completes activation and starts regular operation.

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6.10 Security

6.10.1 Authentication

The XGS-PON system supports several mechanisms for authentication. The first
mechanism is based on the registration ID, which provides a basic level of authentication
for the ONU only and support is mandatory in all XGS-PON devices. The second
mechanism is based on an OMCI message exchange, which provides mutual
authentication. The third mechanism is based on an IEEE 802.1X message exchange,
which provides mutual authentication and a wide range of extensible features.

6.10.2 XGEM Payload Encryption

The encryption key used for unicast traffic is generated by the ONU and transported to
the OLT in PLOAM. When optional XGS-PON upstream encryption is employed, the
same encryption key is used in both the upstream and downstream directions.

6.10.3 Message Integrity Check

The integrity (and data origin) of the PLOAM partitions in the upstream and downstream
XGS TC headers is protected by the 64-bit secure Message Integrity Code (MIC) that
appears at the end of each PLOAM message.

The integrity (and data origin) of the OMCI message in the upstream and downstream is
protected by the 32-bit secure Message Integrity Code (MIC) that appears at the end of
the OMCI message.

6.11 Power Saving

For a variety of reasons, it is desirable to reduce the power consumed by an ONU as

much as possible.

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XGS-PON Technical White Paper

 Over time, the natural evolution of technology tends toward more efficient
realizations of given functions, a tendency that is offset, at least to some extent, by
increasing levels of functionality and speed.

 If there is a way for the ONU to determine that a subscriber interface is idle, it is
desirable for the ONU to power down the circuitry associated with that interface,
while retaining the capability to detect subscriber activity on that interface. The
details vary as a function of the interface type.

 The extent of feasible power reduction depends on the acceptable effect on service.
The maximum possible savings occurs when a subscriber intentionally switches off
an ONU, for example overnight or during a vacation.

 During failures of AC power, some degradation of service is generally acceptable.

To conserve backup battery lifetime, it is desirable for the ONU to power down
circuitry associated with all interfaces except those considered to be essential
services. Different operators and customers will have different definitions of
essential services, and will wish to prioritize the time before which services are
powered down.

The preceding techniques for power management are a matter of ONU design and
subscriber and operator practice, and are beyond the scope of this recommendation.

This clause addresses two additional means of power management, which do require TC
layer support.

One is called Doze mode; the other is referred to as Cyclic Sleep mode. Both are
statically provisioned through OMCI and either or both of these latter modes may be
combined with any or all of the other power reduction techniques.

All G.987.3-compliant implementations are expected to support the Doze mode. Support
of the Cyclic Sleep mode is optional for both OLT and ONU.

6.12 Protection Switchover

Similar to GPON, XGS-PON supports Type B and Type C protection switchover. Refer to
G.984.1 for the protection implementation.

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7 ONU Management and Control Interface

(OMCI)
Optical network unit (ONU) management and control interface (OMCI) for optical access
networks specifies the managed entities of a protocol-independent management
information base (MIB) that models the exchange of information between an optical line
termination (OLT) and an optical network unit (ONU). It covers the ONU management
and control channel, protocol and detailed messages. OMCI fits into the network
architecture reference model for PON described in [ITU-T G.984.1] and [ITU-T G.987

series] as illustrated in Figure 7-1. The dotted line shows a path for OMCI signals

between an OLT and ONU.

Figure 7-1 Reference model, OMCI

As shown in Figure 7-2, the functions of the ONU are:

1. access network line termination;

2. user network interface line termination, noting that in the fibre to the business case,
the UNIs from one ONU may belong to different users;

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3. service multiplexing and de-multiplexing.

Figure 7-2 ONU functional block diagram

The ONU management and control interface is used by the OLT to manage the ONU in
the following areas:

1. configuration management;

2. fault management;

3. performance management;

4. security management.

This interface allows the OLT to:

1. establish and release connections across the ONU;

2. manage the UNIs at the ONU;

3. request configuration information and performance statistics;

The OMCI also allows the ONU to inform the OLT autonomously of alarms, performance
threshold crossings and changes to the values of many of the MIB attributes. The OMCI
protocol is asymmetric: the controller in the OLT is the master, while the ONU is the slave.
A single OLT controller using multiple instances of the protocol over separate control
channels typically controls multiple ONUs.

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7.1 Configuration Management

Configuration management provides functions to identify the ONU’s capabilities and

exercise control over the ONU. Areas of configuration management include:

1. configuration of equipment;

2. configuration of PON and RE protection

3. configuration of the UNIs;

4. configuration of GEM port network CTPs in G-PON applications;

5. configuration of interworking termination points;

6. configuration of OAM flows;

7. configuration of physical ports;

8. configuration of GAL profiles in GPON applications;

9. configuration of service profiles;

10. configuration of traffic descriptors;

11. configuration of AAL profiles, when needed for ADSL UNIs.

7.2 Fault Management

As modelled by OMCI, the ONU detects and reports equipment, software and interface
failures and declares the corresponding alarms. The OMCI supports failure reporting on
many managed entities as described in clause 9. An alarm table is defined for each of
these entities.

In addition to failure reporting, the OMCI supports test, measurement and in-service
monitoring, including

1. Metallic tests of copper drops (voice and/or xDSL)

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2. Optical and other parameters of the optical distribution network

3. [IEEE 802.1] connectivity fault management

4. Directed loopback, for example of DS1/E1 services

The OMCI also provides for reporting of protection switch events.

7.3 Performance Management

The ONU has only limited performance monitoring. The OMCI supports performance
monitoring using a number of managed entities. These managed entities can be
identified by the words “performance monitoring history data” or “extended PM” in their
names. All performance monitoring related managed entities are created at the request
of the OLT. All history data is maintained in the OLT. The ONU maintains only a current
counter and one 15-minute previous-interval counter.

7.4 Security Management

Different access technologies specify differing degrees of security capability [ITU-T

G.984 series], [ITU-T G.986], [ITU-T G.987 series]. OMCI supports a mechanism to allow
mutual authentication of OLT and ONU and subsequent secure communication of
encryption keys.

7.5 ONU Management and Control Protocol

G.988 defines two formats for OMCI messages, baseline and extended. GPON systems
are free to use either the baseline or the extended OMCI message format. The baseline
format is the default at initialization. Use of the extended format is then negotiated

between OLT and ONU. Baseline messages have 48-byte fixed length PDUs, while

extended messages have variable length PDUs. A receiver that does not support
extended messages may therefore reject extended message based on nothing more
than their length.

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Both baseline and extended messages carry a message integrity check (MIC) in their
final four bytes. This facilitates ad hoc recovery of both message types by a receiver. In
G.984 systems, the MIC is an I.363.5 CRC; in G.987 systems, the MIC is a cryptographic
hash as specified in G.987.3.

Baseline and extended messages are distinguished from one another by the device
identifier field, which is in the same byte location in both message types. Baseline
messages contain device identifier 0x0A, while extended messages employ device
identifier 0x0B.

All GPON ONUs and OLTs are required to support the baseline format. During

initialization, and whenever the ONU is re-ranged onto the PON, both entities use the

baseline format to establish communications and to negotiate their capabilities. If both

endpoints support extended messages, they may or may not choose to conduct all or
some subsequent communications in the extended message set. Baseline messages
may be used for any transaction, that is, any exchange of one or more related messages
such as a get/get-next sequence.

Table 7-1 shows the baseline message format. The packet has a fixed length of 48 bytes.

Table 7-2 shows the extended message format. The packet has variable length N, up to

1980 bytes.

Table 7-1 Baseline OMCI Message Format

Byte number Size Use

1..2 2 Transaction correlation identifier

3 1 Message type

4 1 Device identifier

5..8 4 Managed entity identifier

9..40 32 Message contents

41..48 8 OMCI trailer

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Table 7-2 Extended OMCI Message Format

Byte number Size Use

1..2 2 Transaction correlation identifier

3 1 Message type

4 1 Device identifier

5..8 4 Managed entity identifier

9..10 2 Message contents length

11..(N-4) Message contents

-

(N-3)..N 4 Message integrity check MIC

8 Technical Differences among GPON,

XG-ON and XGS-PON

Table 8-1 Technical Differences among GPON, XG-ON and XGS-PON

GPON XG-PON XGS-PON

Standard G.984 G.987 G.9807.1

Nominal line rate DS: 2.5 Gbps; DS: 10 Gbps; DS: 10 Gbps;
US: 1.25 Gbps US: 2.5 Gbps US: 10 Gbps

Split Ratio 1:64/128 1:64/128/256 1:64/128/256

Line code NRZ NRZ NRZ

Operating DS: 1480-1500 nm DS: 1575-1580 nm DS: 1575-1580 nm

wavelength US: 1290-1330 nm US: 1260-1280 nm US: 1260-1280 nm

Max Distance/
40 km/20 km (40 km to be
Differential 20 km/20 km 40 km
defined)
Distance

Max logic
60 km 60 km 60 km
Distance/
20 km 40 km 40 km
Differential logic

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Distance

Encapsulation
GEM XGEM XGEM
Method

FEC DS: RS (248, 216); DS: RS (248, 216);

US/DS: RS (255, 239)
US: RS (248,232) US: RS (248, 216);

Encryption DS: AES DS/US: AES DS/US: AES

Multicast
No support Support Support
Encryption

OMCI Fix length Fix length and variable Fix length and variable
length length

9 Migration towards XGS-PON

9.1 Compatibility between XG-PON and XGS-PON

Figure 9-1 Compatibility between XG-PON and XGS-PON

The OLT XGS-PON port supports the coexistence of XG-PON ONUs and XGS-PON
ONUs via TDMA in upstream and downstream directions, and supports receiving the
data burst at 9.953Gb/s and 2.488Gb/s, thereby suiting diversified scenarios. The same
XGS-PON port supports accessing the business users who demand for symmetric
bandwidth as well as the home users who demand for asymmetric bandwidth, which
meets the requirements of different users and reduces the investment of the carriers on
terminal devices.

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9.2 Coexistence between XGS-PON and GPON through

WDM1r

XGS-PON and GPON can coexist in the same ODN through external WDM1r.

Figure 9-2 Coexistence between XGS-PON and GPON through WDM1r

GPON and XGS-PON can coexist through WDM (Wavelength-Division Multiplexing).

The XGS-PON wavelengths and GPON wavelengths in the upstream and downstream
directions are completely isolated from each other. The four wavelengths can coexist in
the same ODN without interfering with each other. WDM1r is a wavelength combiner,
which combines the GPON downstream wavelength from the GPON interface and the
XGS-PON downstream wavelength from the XGS-PON interface into the same fiber for
transmission, and separates the GPON upstream wavelength and XGS-PON upstream
wavelength from the same fiber to the GPON and XGS-PON interface respectively. This
scenario supports the coexistence of XGS-PON ONUs and XG-PON ONUs under the
same XGS-PON interface.

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10 Conclusions
Based on ITU-T G.987 and ITU-T G.989 series PON standards, XGS-PON expands the
capabilities, providing symmetric large-bandwidth services, and supporting the
coexistence of GPON and RF video in the same ODN as well as the coexistence of
XGS-PON ONUs and the XG-PON ONUs. With the coming of the Gigabit era, XGS-PON
has been gradually mature and commercialized. ZTE takes the lead in XGS-PON
productization and commercialization. The industry’s first ASIC-based high-density
XGS-PON service cards compatible with XG-PON ONUs launched by ZTE is an optimal
choice for the operators to upgrade their networks to 10G-GPON.

11 References
ITU-T G.9807.1 (2016) 10-Gigabit-capable symmetric passive optical network
(XGS-PON)

ITU-T G.988 (2010) ONU management and control interface (OMCI) specification

ITU-T G.984.5 Enhancement band for Gigabit capable Optical Access Networks

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