next-generation pon evolution - huawei.com · 5 the evolution of pon technology and networks ... q2...
TRANSCRIPT
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.
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