Next-Generation PON Evolution

Transcription

1 Next-Generation PON Evolution

2 Next-Generation PON Evolution 1 Overview PON Evolution Basic Principles Evolution Path Smooth Evolution Based on Coexistence: NG-PON Network Architecture, Coexistence and Evolution Physical Layer Specifications TC Layer Specifications Management and Configuration Interoperability A Brand New Technology for Long-Term Evolution NG-PON WDM-PON ODSM-PON Stacked XG-PON Coherent WDM-PON Other Technologies The Evolution of PON Technology and Networks Bandwidth Requirement Drives NG PON Evolution Industry Chain Drives NG PON Evolution NG PON Cost OLT Capability...20

3 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 FT deployment among operators. PON-based FT 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. 1

4 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 (s) 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 longterm 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 2

5 Figure 2-1 NG-PON roadmap by FSAN Current work focus: Selecting the most suitable Technology for NG-PON2 Downstream: 10G Upstream: 2.5G or 5G Coexistence need not be considered. NG-PON2 Downstream: 2.5G Upstream: 1.25G WDM coexistence XG-PON1 ODSM, 40G, WDM, OFDMA G-PON ~2015 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 s. The third prospect is OCDMA-PON. OCDMA-PON uses code division multiple access (CDMA) to encode 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 s, 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. 3

6 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. Figure 3-1 XG-PON1 standardization developments Started G.987.RE Completed G.987.RE draft Standarization developments Completed major architecture Discussed G.987.3/G.988 Technical specifications Wrote and revised G.987/ G.987.1/G Completed framing specifications Completed G Completed the G.988 draft (edition one) Revised jitter parameters Completed and published G.987/G.987.1/G Completed scrambling and security specifications Completed G draft (edition one) and stabilized G.988 Completed extended power budget specifications Further revised G Beijing FSAN/Q2 Completed G.987.3/G.988 Principal standards Completed G revision Completed principal XG-PON1 standards Started enhanced XG-PON1 To publish principal XG-PON1 standards

7 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-multipoint (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. Figure 3-2 XG-PON1 application scenarios XG-PON Cell site Business Residential FTTCell FTTB FTTO FTTH FTTB CBU MTU SBU SFU MDU XG-PON OLT XG-PON OLT Aggregation Switch FTTCurb/Cab 5

8 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, between an 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 (XG-PON) IF XGPON IF XGPON OLT (XG-PON) Logic (XG-PON + video) WDM-X WBF WDM -X-L IF XGPON, IF Video Logic Logic WBF WDM-X IF GPON OLT (G-PON) (G-PON) V- WBF-V IF GPON Splitter WDM1r WDM -G-L Logic Logic WBF WDM-G (G-PON + video) IF GPON, IF Video IF Video OLT (video) Logic WBF WDM-G V- WBF V- WBF-V ODN 6

9 Brownfield scenarios (that is, coexistence with existing deployments) use the pre-existing GPON deployments of operators. As the bandwidth requirement increases, operators can upgrade s 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 must support [ITU-T G 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-PON1 OLT WDMr1 G-PON1 OLT GPON 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 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 nm to promote the technology maturity. 7

10 Table 3-1 XG-PON1 physical layer specifications Optical fiber Item Specifications Remarks Wavelength plan [1] Power budget Line rate [2] Split ratio Maximum physical transmission reach Maximum logical transmission reach Maximum differential logical reach Compliant with [ITU-T G.652] Upstream: 1260 to1280 nm Downstream: 1575 to 1580 nm 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) Upstream: Gbps Downstream: Gbps At least 1:64 Scalable to 1:128 and 1:256 At least 20 km At least 60 km Scalable to 40 km New optical fibers that are compliant with [ITU-T G.657] are applicable to XG-PON1 deployments. Downstream: 1575 to 1581 nm (for outdoor deployments) 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 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 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. 8

11 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 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 The ITU-T Recommendation [G.987.3], aka: the XG-PON1 TC layer standard was officially approved in June 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 9

12 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 s through the OMCI channel. The OLT and the 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 s. 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 userside interface. The 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 s in XG-PON1 is via OMCI. In the FTTB/FTTC scenario, XG-PON1 can manage s 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 10

13 various management requirements in different scenarios. The first draft of [G.988] was completed in February 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 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 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 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. 11

14 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 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 s. 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 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 wavelengthdependent, and the optical transceiver on each 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. 12

15 Figure 4-1 Typical WDM-PON system 用户终端 CO λ1, λ2, λ3, λ4... Remote Node λ1 / / / / / AWG1 AWG2 λ4 λ2 λ3 / / / Figure 4-2 WDM-PON network topology CO AWG AWG AWG Fiber distribution frame WDM-PON Fiber distribution frame AWG AWG 终端用户 1 终端用户 n 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 temperatureinsensitive 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 costinsensitive applications, such as FTTB/FTTbusiness and FTTMobile. 13

16 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 s 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 ODSM OLT Multi Chan MAC Array Array Old CO WDM split A solution shown in Figure 4-3 was proposed in 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 s, 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 s. In the upstream, ODSM PON adopts dynamic TDMA+WDMA. The data transmitted by the GPON/XG-PON1 s 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 at user premises. 14

17 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 upgradeas-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 s should be replaced by colored s, while the s are untouched in OSDM-PON. Figure 4-4 Stacked XGPON CO XGPON1 OLT XGPON1 ONT XGPON1 OLT WDM SP XGPON1 ONT XGPON1 OLT XGPON1 ONT 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 select wavelengths according to the principle of coherent detection. This means the OLT and start coherent 15

18 Figure 4-5 Coherent WDM-PON X X X X X X X X Modulator L.O. #N Pol. Div. Coh. OLT Pol. Div. Coh. Local Osc. Modulator DSP Control Freq. Gen. 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 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 s 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. 16

19 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. Figure 5-1 Roadmap of bandwidth requirement for FTTB/C 10G PON Upgraded to 10G GPON Adopt FTTB/C/H Upgrade ADSL2+ to VDSL2 GPON 2011: IPTV ratio: 10%, 30% being internet service Per-user bandwidth 20M MDU Us BW (24 users) 67.2M PON Ds BW 1.07G 2013: IPTV ratio: 40%, 60% being internet service Per-user bandwidth 50M MDU Us BW (24 users) 187.8M PON Ds BW 3.0G DSLAM Note: split ratio: 1:16; concurrency: 50%; installation ratio: 75% G 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. 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 17

20 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. Figure 5-2 Roadmap of rate-rise for FTTH 10G PON GPON 2013: IPTV ratio: 40%, 60% being internet service Per-user bandwidth 50M GPON Ds BW (1:128) 1440M Upgraded to 10G GPON High HD service adoption rate 2015: IPTV ratio: 60%, 40% being internet service Per-user bandwidth 100M 10G GPON Ds BW 1980M (1:128) DSLAM 2011: IPTV ratio: 10%, 30% being internet service Per-user bandwidth 20M GPON Ds BW (1:128) 867M Note: concurrency: 50%; installation ratio: 75% Industry Chain Drives NG PON Evolution 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 12% 37% 19% Optics PON Chipset PCB R/C IC 32% 18

21 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 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 15% 45% 10% Optics PON Chipset Common part Service card 30% 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) Multiple mow k k 2015 Scale Year 19

22 Therefore, it is anticipated that 10G PON will enter small scale commercial application for FTTB/C in 2013, and large scale commercial application in 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 users, and an OLT system connected to 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 k 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. 20

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