Next-Generation PON Evolution

Next-Generation PON Evolution

1 Overview .......................................................................................................................1

2 PON Evolution ...............................................................................................................2

2.1 Basic Principles ..............................................................................................................2

2.2 Evolution Path ...............................................................................................................2

3 Smooth Evolution Based on Coexistence: NG-PON1 .......................................................4

3.1 Network Architecture, Coexistence and Evolution .........................................................5

3.2 Physical Layer Specifications ..........................................................................................7

3.3 TC Layer Specifications ..................................................................................................9

3.4 Management and Configuration ....................................................................................9

3.5 Interoperability ............................................................................................................11

4 A Brand New Technology for Long-Term Evolution–NG-PON2 .....................................12

4.1 WDM-PON ..................................................................................................................12

4.2 ODSM-PON .................................................................................................................14

4.3 Stacked XG-PON .........................................................................................................15

4.4 Coherent WDM-PON ...................................................................................................15

4.5 Other Technologies ......................................................................................................16

5 The Evolution of PON Technology and Networks .........................................................17

5.1 Bandwidth Requirement Drives NG PON Evolution ......................................................17

5.2 Industry Chain Drives NG PON Evolution ......................................................................18

5.2.1 NG PON Cost ........................................................................................................................................18

5.2.2 OLT Capability .......................................................................................................................................20

1

1 Overview

A passive optical network (PON) features a point-to-multi-point (P2MP)

architecture to provide broadband access. The P2MP architecture has become

the most popular solution for FTTx deployment among operators. PON-based

FTTx has been widely deployed ever since 2004 when ITU-T Study Group 15

Q2 completed recommendations that defined GPON system [ITU-T series

G.984].

As full services are provisioned by the massive deployment of PON networks

worldwide, operators expect more from PONs. These include improved

bandwidths and service support capabilities as well as enhanced performance

of access nodes and supportive equipment over their existing PON networks.

The direction of PON evolution is a key issue for the telecom industry.

Full Service Access Network (FSAN) and ITU-T are the PON interest group

and standard organization, respectively. In their view, the next-generation

PONs are divided into two phases: NG-PON1 and NG-PON2. Mid-term

upgrades in PON networks are defined as NG-PON1, while NG-PON2 is a

long-term solution in PON evolution. Major requirements of NG-PON1 are

the coexistence with the deployed GPON systems and the reuse of outside

plant. The aforementioned requirements were tested in the recent Verizon

field trials. Optical distribution networks (ODNs) account for 70% of the

total investments in deploying PONs. Therefore, it is crucial for the NG-

PON evolution to be compatible with the deployed networks. With the

specification of system coexistence and ODN reuse, the only hold-up of the

migration from GPON to NG-PON1 is the maturity of the industry chain.

Unlike NG-PON1 that has clear goals and emerging developments, there

are many candidate technologies for NG-PON2. The selection of NG-PON2

is under discussion. However, one thing is clear, NG-PON2 technology

must outperform NG-PON1 technologies in terms of ODN compatibility,

bandwidth, capacity, and cost-efficiency.

This paper describes the design principles and prospective technologies for

NG-PONs. It introduces Huawei’s views of NG-PON evolution, focusing on

the discussion and evaluation of various technologies. All of the discussion

follows the FSAN and ITU-T framework of NG-PON recommendations.

2

2 PON Evolution

2.1 Basic Principles

Ultra broadband and co-existence with existing technologies are the general

requirements from network operations to direct PON evolution.

Operators worldwide are seeking to increase revenue by developing

bandwidth-consuming services. An exemplified service is HDTV, which requires

about 20 Mbit/s per channel. In the near future, new business models, such

as home video editing, online gaming, interactive E-learning, remote medical

services, and next-generation 3D TV will dramatically increase bandwidth

demand.

The deployment of PON generally implies considerablely initial investments

and slow return on investment (ROI). ODN deployment accounts for 76% of

the total investments in greenfield FTTH networks, while optical network units

(ONUs) account for 21%. Protecting investments by leveraging existing ODNs

is essential to operators.

2.2 Evolution Path

After GPON Recommendations were done, FSAN and ITU-T continued the

study of NG-PONs and defined the first phase of NG-PONs as systems that

offer low costs, large capacity, wide coverage, full service, and interoperability

with existing technology. FSAN and ITU-T members also agree that long-

term PON evolution will be driven by new scenarios if coexistence with legacy

systems is not required. In addition to time-division multiplexing (TDM) PONs,

other technologies for NG-PON could also be taken into account.

Based on the current application demands and technological maturity, FSAN

divides NG-PONs into two phases shown in Figure 2-1.

As indicated in Figure 1, FSAN divide NG-PON evolution into NG-PON1 and

NG-PON2. NG-PON1 is a mid-term upgrade, which is compatible with legacy

GPON ODNs. NG-PON2 is a long-term solution in PON evolution that can be

deployed over new ODNs, independent of GPON standards.

The selection of NG-PON1in FSAN is a trade-off between technology and

cost. Operators require that NG-PON1 systems have a higher capacity,

longer reach, larger bandwidth, and more users. Operators also require that

3

G-PON

XG-PON1

NG-PON2

Downstream: 2.5GUpstream: 1.25G

2004 2010 ~2015

WDM coexistence

Coexistence need not be considered.

Current work focus:Selecting the most suitableTechnology for NG-PON2

ODSM, 40G, WDM,OFDMA……

Downstream: 10GUpstream: 2.5G or 5G

Figure 2-1 NG-PON roadmap by FSAN

NG-PON1 should leverage the use of existing GPON ODN to control cost.

Moreover, driven by services, the downstream bandwidth demands will

outpace upstream bandwidth demands for a long period. Therefore, FSAN

decided to define NG-PON1 as an asymmetric 10G system with rates of 10G

downstream and 2.5G upstream. The selected NG-PON1 system is essentially

an enhanced TDM PON from GPON.

Unlike NG-PON1, there are several types of prospective technologies that can

be adopted for NG-PON2. Among the prospective technologies, a suggested

baseline is to improve the rate to 40G from 10G by following the TDM

technology. The second method is the employment of wavelength division

multiplexing (WDM) PON to achieve 40G access. The possible multiplexing

schemes can be coarse wavelength division multiplexing (CWDM) or dense

wavelength division multiplexing (DWDM). The ODSM PON topology

based on TDMA+WDMA is also suggested, which dynamically manages

user spectrum without modifying the ODN and ONUs. The third prospect

is OCDMA-PON. OCDMA-PON uses code division multiple access (CDMA)

to encode ONU singals, thereby avoiding the timeslot assignment for data

transmission required by a time division multiple access (TDMA) systems. The

O-OFDMA PON topology is an option that uses orthogonal frequency division

multiple access (OFDMA) technology to differentiate ONUs, thus effectively

improving bandwidth usage. However, most of these technologies are still in

the research phase. More study and test are highly desired to promote them

as industry standard.

4

3 Smooth Evolution Based on Coexistence: NG-PON1

A general requirement of NG-PON1 is to provide higher data transmission

rates than GPON. In addition, operators expect NG-PON1 to leverage

existing optical deployments. Hence, FSAN and ITU-T specified the NG-PON1

backward compatibility with legacy GPON deployments to protect the initial

GPON investments of operators.

The specified NG-PON1 system is called XG-PON1. In an XG-PON1 system,

the upstream rate is 2.5G and the downstream rate is 10G. Therefore, the

downstream bandwidth of XG-PON1 is four times of that of GPON, while the

upstream bandwidth of XG-PON1 is twice as that of GPON. Particularly, the

ODN in XG-PON1 entirely inherits that of GPON, implying that optical fibers

and splitters in legacy GPON systems can be reused in XG-PON1. After a 10G

interface board is added to the OLT, smooth evolution from GPON to XG-

PON1 can be achieved, which completely leverages the value of GPON ODN.

Standarization developments

StartedenhancedXG-PON1

To publish principal XG-PON1 standards

Completed principal XG-PON1 standards

BeijingFSAN/Q2

200906 200910 201002 201006 201008

Principalstandards

CompletedG.987.2 revision

Completed G.987.3/G.988

Completed G.987.RE draft

Wrote and revised G.987/G.987.1/G.987.2

Discussed G.987.3/G.988Technical specifications

Completed majorarchitecture

Revised jitterparameters

Completed and publishedG.987/G.987.1/G.987.2

Completed framingspecifications

Completed G.987.3Completed the G.988draft (edition one)

Completed scrambling and security specifications

Completed extended power budget specifications

Further revised G.987.2

Completed G.987.3draft (edition one) andstabilized G.988

Started G.987.RE

Figure 3-1 XG-PON1 standardization developments

5

As an enhancement to GPON, XG-PON1 inherits the framing and

management from GPON. XG-PON1 provides full-service operations via

higher rate and larger split to support a flattened PON network structure.

The baseline XG-PON1 standards have been completed. In October 2009,

ITU-T consented general requirements and physical layer specifications of

XG-PON1 and published them in March 2010, announcing the NG-PON era.

In June 2010, the transmission convergence (TC) layer and optical network

termination management and control interface (OMCI) standards for XG-

PON1 were consented in the general meeting of ITU-T SG15, and these

standards will be published soon.

Figure 3-1 shows the XG-PON1 standardization developments.

3.1 Network Architecture, Coexistence and Evolution

XG-PON1 is an enhancement to GPON. It inherits the point-to-multi-

point (P2MP) architecture of GPON and is able to support diverse access

scenarios, such as fiber to the home (FTTH), fiber to the cell (FTTCell), fiber

to the building (FTTB), fiber to the curb (FTTCurb), and fiber to the cabinet

(FTTCabinet). The application scenarios of XG-PON1 are shown in Figure 3-2.

XG-PON

AggregationSwitch

XG-PONOLT

XG-PONOLT

CBU

FTTCell

FTTB

FTTO

FTTH

FTTB

FTTCurb/Cab

MTU

SBU

SFU

MDU

ONU

Cell site

BusinessResidential

Figure 3-2 XG-PON1 application scenarios

6

XG-PON1 coexists with GPON over the same ODN, thereby protecting the

investments of operators on GPON. As indicated in XG-PON1 physical layer

specifications, the upstream/downstream wavelength of XG-PON1 is different

from that of GPON. Compatibility between XG-PON1 and GPON is achieved

by implementing WDM in the downstream and WDMA in the upstream. That

is, a WDM1r is deployed at the central office (CO) and a WBF is deployed

at the user side (could be located inside an ONU, between an ONU and

an optical splitter, or on an optical splitter) to multiplex or demultiplex

wavelengths on multiple signals in downstream and upstream directions. The

coexistence of GPON and XG-PON1 is shown in Figure 3-3.

FSAN and ITU-T have proposed two evolution scenarios to greenfield and.

Brownfield.

Greenfield scenarios do not have any pre-existing optical fiber deployments.

Hence, these scenarios can use XG-PON1 to replace legacy copper line

systems. Greenfield scenarios require the deployment of new PON systems,

which are straight-forward; therefore, this paper does not describe it in detail.

Figure 3-3 XG-PON1 & GPON coexistence by WDM1r

ONU (G-PON)

WDM-GLogicTx

Rx WBF

ONU (G-PON + video)

WDM-G’Logic

Tx

Rx WBF

V-Rx WBF-V

ONU (XG-PON) OLT (XG-PON)

WDM-XLogicTx

Rx WBF WDM-X-L

Rx

Tx

Logic

WDM-G-L

Rx

Tx

Logic

V-TxWBF

OLT (video)

ONU (XG-PON + video)

IF XGPON

IF GPON

IF XGPON, IF Video

IF GPON, IF Video IF Video

IF GPON

IF XGPON

ODN

OLT (G-PON)WDM-X’

Splitter WDM1r

LogicTx

Rx WBF

V-Rx WBF-V

7

Brownfield scenarios (that is, coexistence with existing deployments) use the

pre-existing GPON deployments of operators. As the bandwidth requirement

increases, operators can upgrade ONUs over the ODN batch by batch or all at

once when migrating to XG-PON1. The selection between these two types of

upgrades is decided by how long GPON and XG-PON1 will be coexist in the

same ODN.

To achieve a successful GPON-to-XG-PON1 upgrade, the OLT and each ONU

must support [ITU-T G.984.5 AMD 1] compliant wavelength plans. Figure 3-4

shows coexistence of GPON and XG-PON1 using WDM stacking.

Figure 3-4 GPON & XG-PON1 coexistence using WDM stacking

Key technology: WDM stacking

XG-PON1OLT

WDMr1 G-PON1OLT

ONU

ONU

ONU

ONU

ONU

ONU

ONUGPON and XGPON1 use the same 1:32 optical splitter for optical splitting. Every GPON user enjoys a bandwidth of about 80 Mbit/s (downstream)/40 Mbit/s (upstream) and every XGPON1 user enjoys a bandwidth of about 320 Mbit/s (downstream)/80 Mbit/s (upstream).

3.2 Physical Layer Specifications

XG-PON1 physical layer specifications were finalized in October 2009 and

published by ITU-T in March 2010. Table 3-1 lists the detailed specifications

for XG-PON1.

[1] XG-PON1wavelength plan was a hot topic discussed in FSAN by vendors

as well as operators. Driven by the 10G optical transceivers market, FSAN

selected the downstream wavelength of 1575–1580 nm to promote the

technology maturity.

8

Table 3-1 XG-PON1 physical layer specifications

Item Specifications Remarks

Optical fiber Compliant with [ITU-T G.652]New optical fibers that are compliant with [ITU-T G.657] are applicable to XG-PON1 deployments.

Wavelength plan [1] Upstream: 1260 to1280 nmDownstream: 1575 to 1580 nm

Downstream: 1575 to 1581 nm (for outdoor deployments)

Power budget

N1: 14 to 29 dB (for applications that are not co-existent) N2: 16 to 31 dB (used for applications that are coexistent; these figures include WDM1r insertion loss)Extra budget: minimum of 33 dB, scalable to 35 dB)

Line rate [2] Upstream: 2.48832 GbpsDownstream: 9.95328 Gbps

Split ratioAt least 1:64Scalable to 1:128 and 1:256

Maximum physical transmission reach

At least 20 km

Maximum logical transmission reach

At least 60 km

Maximum differential logical reach

Scalable to 40 km

C band. L band, and O band were compared in the selection of upstream

wavelength.. The first option of C band was eliminated because it overlaps

with for the RF video channel. The L band was also eliminated due to the

insufficient guard band between upstream and downstream wavelengths.

The candidate wavelength was narrowed down to O- band and O+ band.

After comparing the pros and cons (such as complexity and costs), O- band

was selected because O+ band has higher requirements on filters.

[2] The downstream rate of XG-PON1 was specified to 10 Gbps, which was

driven by the well-established and low-cost 10 Gbps continuous transmission

technology in the industry. The exact rate is determined as 9.95328 Gbps to

keep the consistency with typical ITU-T rates. This is different from the rate of

the IEEE 10GE-PON, which is in the rate of 10.3125 Gbps. There were 2.5G

and 10G proposals for the XG-PON1 upstream rate. After carefully studying

application scenarios and component cost, 2.5G upstream rate was selected

for specification. The 10G upstream system was not considered as the focus,

mainly due to its high cost and limited application scenarios in the near

future.

9

3.3 TC Layer Specifications

The XG-PON1 transmission convergence (XGTC) layer optimizes the basic

processing mechanisms of the GPON TC layer by enhancing the framing

structure, dynamic bandwidth assignment (DBA), and activation mechanisms.

XG-PON1 enhances the GPON framing by aligning the frame and field

design to word boundaries. This framing structure matches the rate of XG-

PON1. It is easy to implement with chips, and improves the efficiency of

data fragmentation, reassembling, and processing. The DBA mechanism in

XG-PON1 is basically upgraded by offering better flexibility. The activation

mechanism of XG-PON1 follows the principles of GPON.

Improved security and power saving are the two major features of the XGTC

layer.

In GPON, data encryption is optional and security related management is

facilitated via OMCI. In XG-PON1, operators require enhanced security from

the very initial procedure of PON activation. XG-PON1 standards specify

three methods of authentication. The first is an ONU authentication scheme

based on a registration ID (a logical ID used for authentication). The second

method is a bidirectional authentication scheme based on OMCI channels

(inherited from GPON). The third method is a new bidirectional authentication

scheme based on IEEE 802.1x protocols. The XGTC layer also provides new

security mechanisms, such as upstream encryption and downstream multicast

encryption.

Power saving in GPON was an afterward thought. The ITU-T published

[G.sup45] on saving power with multiple modes at the chip level. Operators

propose mandatory regulations and improvements on XG-PON1 to promote

power saving worldwide. XG-PON1 supports doze mode and cyclic sleep

mode specified in [G.sup45]. Vendors are also allowed to independently

extend power saving techniques.

The draft of XGTC layer standard was completed in April 2010. The ITU-T

Recommendation [G.987.3], aka: the XG-PON1 TC layer standard was

officially approved in June 2010.

3.4 Management and Configuration

The management and configuration of XG-PON1 should not be impacted by

the changes of lower-layer technologies. Therefore, ITU-T Recommendation

[G.984.4] was adopted as the baseline for standard development. This further

10

facilitates backward compatibility with GPON and minimizing of changes.

OMCI management is a management mechanism in GPON that carries OMCI

data over a special GEM connection. The special GEM connection is also

called an OMCI channel. An OLT manages and configures ONUs through the

OMCI channel. The OLT and the ONU exchange management information

base (MIB) information to establish and maintain an OMCI model. OMCI

management and configuration covers configuration management, fault

management, performance management, and security management of the

ONUs.

XG-PON1 inherits almost 90% of the GPON OMCI technology with minor

modifications to [G.984.4]. Consider the management and configuration

of a Layer-2 data service as an example. As far as the service is concerned,

it does not matter which specific lower-layer technology is adopted. The

key point is that a Layer-2 channel should be properly configured to ensure

normal forwarding of service data. The OMCI L2 model covers all possible L2

configurations from the network side to the user side (ANI-TCONT-GEM-MAC

bridge-UNI). This model is applicable to GPON as well as to XG-PON1 because

they both have the same definitions for the network-side channel and user-

side interface.

The ONU management and configuration mechanisms are pretty stable from

A /B-PON to GPON and to XG-PON1. Therefore, it was decided that the ITU-

T's TDM PON series require only one general OMCI standard that is applicable

to all PON systems. This is the concept of generic OMCI, which gained wide

recognition and support from the industry. ITU-T/Q2 applied for an ITU-T

program numbered [G.988] for the Generic OMCI Standard to distinguish the

standard from the PON system. The [G.988] document was developed based

on the latest version of [G.984.4]. The difference is that [G.988] excludes

descriptions that are specifically related to the technical features of PONs. In

this way, [G.988] is specified to cover the general OMCI in PONs.

The terminal management of XG-PON1 fully retains the GPON features. In the

FTTH scenario, the default management of ONUs in XG-PON1 is via OMCI.

In the FTTB/FTTC scenario, XG-PON1 can manage ONUs through OMCI or

other management protocols (i.e., dual management). The dual management

mechanism is to first set up an OMCI channel, which serves as the Layer-2

channel required by other management protocols for interoperation;

then, use the virtual port of the OMCI as a division point for transparently

transmitting the packets of other management protocols over the PON link.

The flexibility of dual management enables GPON and XG-PON1 to address

11

various management requirements in different scenarios.

The first draft of [G.988] was completed in February 2010. In April 2010, the

official draft of [G.988] was finished. In June 2010, [G.988] was approved by

ITU-T.

3.5 Interoperability

Interoperability is the most impressive feature of GPON and XG-PON1.

FSAN established the OMCI implementation study group (OISG) in 2008

during the GPON era. The group members were restricted to system vendors

and chip vendors to study the [G.984.4] OMCI interoperability specification.

The [G.984.4] Recommendation defines the establishment of an ONT

management and control channel (OMCC), update of the MIB after an ONU

goes online, MIB/alarm synchronization, software version upgrade, L2 service

configuration, multicast configuration, and QoS management. The first

edition of [G.984.4] was finished in December 2008 and second edition was

finished in October 2009. Both editions were approved and quickly released

by ITU-T. The official number of [G.984.4] is [ITU-T G.impl984.4] and is also

called the OMCI implementation guide. Since then, FSAN has been using

[G.impl984.4] as the primary specification for interoperability test cases. Three

interoperability tests were performed between 2009 and the first half of

2010. After the interoperability tests were completed in the first half of 2010,

FSAN operators were satisfied with the test results and did press release to

highlight the superb interoperability of GPON. FSAN considers the GPON

interoperability test has reached a remarkable milestone and the further

research of this subject will be conducted in the broadband forum (BBF, the

original DSL forum). FSAN will move on to the interoperability testing of XG-

PON1.

[G.988] Recommendation basically adopts [G.impl984.4] directly. Hence, the

mandatory appendix of [G.988] incorporates all contents of [G.impl984.4],

meaning that XG-PON1 inherits the superb interoperability of GPON.

12

4 A Brand New Technology for Long-Term Evolution–NG-PON2

The selection of XG-PON1 is driven by technology availability and economic

reasons. When evolving from NG-PON1 to NG-PON2, however, more

technologies are available for long-term evolution. Therefore, upgrades

with more intense innovations can be envisioned. In the FSAN NG-PON2

workshops, items discussed include 40G, WDM PON, OFDMA, etc..

4.1 WDM-PON

A typical wavelength division multiplexing PON (WDM-PON) architecture is

shown in Figure 4-1. The wavelength division MUX/DEMUX is employed in the

ODN. In the example in Figure 4-1, array waveguide gratings (AWGs) are used

to MUX and DEMUX wavelengths to or from ONUs. Signal transmission in

WDM-PON is similar to that in the point to point GE (P2P GE). The difference

between the two systems is that WDM-PON is based on the isolation of

different wavelengths on the same optical fiber. Each ONU in WDM-PON

exclusively enjoys the bandwidth resources of a wavelength. In other words,

WDM-PON features a logical P2MP topology, as shown in Figure 4-2.

In the WDM-PON system in Figure 4-1, each port of the AWG is wavelength-

dependent, and the optical transceiver on each ONU must transmit optical

signals in a specified wavelength determined by the port on the AWG. Optical

transceivers with specified wavelengths are called colored optical transceivers.

Colored optical transceivers introduce complexity in processes such as

service provisioning and device storage. In addition, AWG components are

sensitive to temperature. Therefore, WDM-PON has the following two major

challenges.

Challenge 1: Addressing the real-time consistency between the wavelength of

optical transceivers and the connecting AWG port.

Colorless optical source technology is used to resolve this issue. Colorless

optical source solutions can be classified into tunable laser and seeded laser

according to whether a seed source is involved. According to the source of

the seed light, the solutions can be further defined as self-injection, external

injection (including ASE seed light injection and array laser injection), and

wavelength re-use.

13

CORemoteNode

λ1

λ2

λ3

λ4

λ1, λ2, λ3, λ4...

Tx/Rx

Tx/Rx

用户终端

Tx/Rx

Tx/Rx

Tx/Rx

Tx/Rx

Tx/Rx

Tx/Rx

AW

G1

AW

G2

Figure 4-1 Typical WDM-PON system

Challenge 2: Addressing the real-time consistency between the wavelengths

of the port on the local AWG (at the CO) and the port on the remote AWG.

Wavelength alignment technology is used to resolve this issue. Wavelength

alignment technology includes optical power monitoring and temperature-

insensitive AWG. Optical power monitoring was a solution proposed in

the early stage of WDM-PON research. The recent solution to wavelength

alignment is the temperature-insensitive AWG technology.

In addition to the aforementioned issues, other challenging factors to WDM-

PON include the industry chain maturity, technology availability, cost, and

insufficient bandwidth drive from the end users. It is not anticipated to have

large scale deployment of WDM-PON in FTTH scenarios in the next 3–5

years. WDM-PON may, however, have fans in bandwidth-hungry and cost-

insensitive applications, such as FTTB/FTTbusiness and FTTMobile.

Figure 4-2 WDM-PON network topology

CO

WDM-PON

Fiber distributionframe

Fiber distributionframe

RxTx

RxTx

终端用户1

RxTx

终端用户n

RxTx

AW

G

RxTx

RxTx

AW

G

AW

G

RxTx

RxTx

AW

GA

WG

14

4.2 ODSM-PON

Opportunistic and dynamic spectrum management PON (ODSM-PON) was

proposed a couple of years ago. It addresses operator requirements in exploiting

the potential of deployed networks for smooth network evolution. It keeps the

ODN and ONUs untouched, providing a salient solution to CO consolidation

and cost control. End users in ODSM-PON enjoy the new communication

experience made available by optical broadband with affordable cost.

Figure 4-3 ODSM PON

Old CO

ONUONU

ONU

ONUONU

ONU

ONUONU

ONU

ONUONU

ONU

ONUONU

ONU

ONUONU

ONU

ONUONU

ONU

ONUONU

ONU

ODSM OLT

MultiChanMAC

TxArray

RxArray

WDMsplit

A solution shown in Figure 4-3 was proposed in 2010. In this solution, the four

GPON/XG-PON1 OLT line cards previously deployed at the "Old CO" can be

replaced with one passive WDM splitter for network upgrade. The network from

the CO to user premises remains unchanged after the upgrade. The new ODSM

OLT communicates with GPON/XG-PON1 ONUs, as demonstrated by Figure 4-3.

In the downstream, ODSM-PON adopts WDM. The data carried over various

wavelengths transmitted by the OLT transmitter array is split by the WDM

splitter and then distributed to GPON/XG-PON1 ONUs. In the upstream,

ODSM PON adopts dynamic TDMA+WDMA. The data transmitted by the

GPON/XG-PON1 ONUs is combined by the WDM splitter and then transmitted

to the OLT receiver array.

ODSM-PON has the following features:

Leverages the existing ODN from the CO to user premises. •

Leverages the existing ONU at user premises. •

15

Cost reduction and power saving with the passive “Old CO”. •

Substantially improves (by 10-fold) the fiber sharing between the CO and •

metro devices.

Follows GPON/XG-PON1 deployment policies by,allowing for an upgrade- •

as-required mode.

ODSM PON offers a brand new choice to the industry.

4.3 Stacked XG-PON

Stacked XG-PON is one of the candidate technologies for NG-PON2. As

shown in Figure 4-4, multiple XG-PON1 sub-networks share one ODN by

using WDM. Each XG-PON1 works independently on a separate wavelength

pair. The wavelengths can be fixed or variable. Wavelength plan is the key

issue for stacked XG-PON. When deploying stacked XG-PON, the XG-PON1

ONUs should be replaced by colored ONUs, while the ONUs are untouched in

OSDM-PON.

XGPON1 ONT

XGPON1 ONT

XGPON1 ONT

XGPON1 OLT

XGPON1 OLT

XGPON1 OLT

WD

M SP

CO

Figure 4-4 Stacked XGPON

A similar proposal of stacked G-PON technology was discussed in the FSAN

NG-PON1 study period. FSAN members conclude that it was more of a

network deployment technology than a system required standards. When the

focus of the standardization was recently shifted to NG-PON2, stacked XG-

PON became one of the study topics once again.

4.4 Coherent WDM-PON

Coherent WDM-PON is also a candidate technology for NG-PON2. As shown

in Figure 4-5, both OLT and ONU select wavelengths according to the

principle of coherent detection. This means the OLT and ONU start coherent

16

Figure 4-5 Coherent WDM-PON

ONUOLTX

X

X

X

X

X

X

X

DSP

Control

Pol. Div.Coh. Rx

LocalOsc.

Modulator

Freq.Gen.

L.O.#N

Modulator

Pol. Div.Coh. Rx

reception only when the locally-oscillated light and signal light meet the

coherent conditions of frequency, phase, and polarization. In this way, the

OLT and ONU can select their wavelengths by dynamically changing their

locally-oscillated light frequencies. Furthermore, coherent WDM-PON uses

passive technology to resolve the issue of power budget.

Coherent WDM-PON directly applies the optical coherent transport

technology into the optical access networks. This introduces the concern of

cost control, which is the design principle of any access technologies. Beside,

the ONUs in coherent WDM-PON are more complicated that those in other

NG-PON2 technologies. Such a technology is more in the status of research

and lab demo. Concerns to cost and complexity challenge its applicability in

the access network.

4.5 Other Technologies

In addition to the NG-PON2 technologies discussed above, some vendors

and research institutions proposed other technologies. There are: OFDMA

PON, tunable hybrid PON, and (O)CDMA PON. OFDMA PON implements

orthogonal frequency division multiplexing in the electrical spectrum. Tunable

hybrid PON adopts tunable transmitters and tunable receivers in its terminals.

(O)CDMA PON distinguishes the communications links between OLT and ONT

and implements multiplexing by encoding the electrical domain (CDMA) or

optical domain (OCDMA) in the upstream and downstream directions.

These technologies are off the mainstream as there are serious cost

bottlenecks due to technical complexity and immaturity. Most of them are

under lab research. The PON industry does not anticipate fast revolution in

the related areas of these technologies, and further research is needed.

17

10G PON

GPON

DSLAM

2009 2010 20122011 2013

Note: split ratio: 1:16; concurrency: 50%; installation ratio: 75%

2011: IPTV ratio: 10%, 30% beinginternet service

Upgraded to 10G GPONAdopt FTTB/C/HUpgrade ADSL2+ to VDSL2

2013: IPTV ratio: 40%, 60% beinginternet service

Per-user bandwidth

MDU Us BW (24 users)

PON Ds BW

20M

67.2M

1.07G

Per-user bandwidth

MDU Us BW (24 users)

PON Ds BW

50M

187.8M

3.0G

Figure 5-1 Roadmap of bandwidth requirement for FTTB/C

5 The Evolution of PON Technology and Networks

5.1 Bandwidth Requirement Drives NG PON Evolution

As PON technology advances from 1G to 10G and even higher rates,

operators are gearing up for a future user bandwidth requirement to 100M

and even 1G. The mainstream bandwidth requirement is targeted as 100M

for residential users and 1G for commercial users in the next 5–10 years. The

following figure forecasts the bandwidth requirement increase for FTTB/C and

FTTH scenarios.

10G PON supports a maximum 10G downstream rate, which can

accommodate the access requirements of future users. On the issue of PON

cost, however, 10G PON will cost 3–5 times of GPON in the next 2–3 years.

Considering the enormous network deployment cost, FTTB/C scenarios are

the initial applications of 10G PON, where cost can be shared among more

users.

ONU cost takes up about 60% of the total cost of FTTH equipment.

Therefore, the large scale deployment of 10G PON in the FTTH scenario

depends on the development of the chips and optical components for 10G

PON. It is anticipated that, in 2015, the cost of 10G PON products will be

18

approximately the same as that of the current GPON products. Therefore, by

2015, operators can select 10G PON to increase the bandwidth of residential

users to 100M and commercial users to 1G.

10G PON

GPON

DSLAM

2009 2010 2012 2013 20142011 2015

Note: concurrency: 50%; installation ratio: 75%

2013: IPTV ratio: 40%, 60% being internet service

Per-user bandwidth

GPON Ds BW (1:128)

50M

1440M

Upgraded to 10G GPONHigh HD service adoption rate

2015: IPTV ratio: 60%, 40% beinginternet service

Per-user bandwidth

10G GPON Ds BW

(1:128)

100M

1980M

2011: IPTV ratio: 10%, 30% being internet service

Per-user bandwidth

GPON Ds BW (1:128)

20M

867M

Figure 5-2 Roadmap of rate-rise for FTTH

5.2 Industry Chain Drives NG PON Evolution

5.2.1 NG PON Cost

Component vendors are at the first stage of the industry chain. They develop

ASIC chips and optical transceivers only after NG PON standards are released.

The ASIC chips and optical transceivers are the core of an NG PON system.

Huawei and other GPON system vendors can provide 10G PON prototypes.

Huawei fulfilled the world’s first 10G PON demo and field trail. The field trail

was in a Verizon network. Cost of 10G PONs is high. Considering a current

ONT as an example, the cost distribution of the main components is as

follows:

Figure 5-3 Cost distribution of the ONT

Optics

PON Chipset

PCB

R/C IC

32%

37%12%

19%

19

Optical components and PON chipset account for over 60% of the total

ONT cost. Meanwhile, the cost of current 10G PON optical components and

chipset are 30–50 times higher than those of GPON's. Therefore, large scale

application of ONT products relies on cost reduction.

MDU, which is for FTTB/C, has a different cost distribution in ONT. See the

following figure.

Figure 5-4 Cost distribution of the MDU

Optics

PON Chipset

Common part

Service card

30%

10%

15%

45%

The cost of the optical transceiver and PON chipset of an MDU take up only

about 25% of the total cost. At the same time, a single FTTB/C MDU usually

services over 24 users and the per-user cost is lower. The cost of MDU optical

components and PON chipsets will be affordable if falling down to 4–6 times

of current GPON components. With the growth of 10G PON users, 10G PON

is estimated to reach a 500k scale in 2013 when the costs will drop to 2-3

times of GPON. The following figure shows the estimated data.

Figure 5-5 Optical component costs (10G PON vs GPON)

50

mow2010

Multiple

ScaleYear

500k2013

5000k2015

60

50

40

30

20

10

0

4-63

20

Therefore, it is anticipated that 10G PON will enter small scale commercial

application for FTTB/C in 2013, and large scale commercial application in

2015.

5.2.2 OLT Capability

10G PON raises new challenges on the system architecture design and

performance of the OLT. The backplane of the OLT must evolve smoothly to

protect existing investments of operators.

The per-slot bandwidth of the backplane needs to be increased from the

current GE/10GE to 40G/80G. This is to address the bandwidth requirements

of future optical access.

The OLT needs to support a larger number of users. Considering the

example of 10G PON in FTTC, FTTC usually covers 200–300 users, and an

OLT system connected to 200–300 FTTC MDUs. This means that an OLT

will accommodate 40k–90k access users. Assuming that each user has four

MAC addresses, a single OLT system will need to support 2566–512k MAC

addresses.

10G PON line cards must be slot compatible with current PON line cards for

higher network flexibility.

In terms of network maintenance and management, the unified network

management system (NMS) is required to manage PON ports and 10G

PON ports at the same time with higher O&M efficiency and lower O&M

expenditure.

To sum up, large capacities, shared platforms, and unified network

management systems will be the trends in 10G PON equipment developments

that vendors are striving to fulfill.

21

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