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The deployment of 10G PON technology has become an industry consensus

Communication world · intensive reading|The deployment of 10G PON technology has become an industry consensus, PON integration has a long way to go.

In the active promotion of “Broadband China” and “increase speed and Reduce costs”, The role of Broadband network as a basic platform for economic and social development has become increasingly prominent; The Internet video application is quickly popularized, 4K / 8K HD, home cloud, video calls and other high-bandwidth business are also evolving. In response to fierce market competition, operators have generally provided Fast Ethernet (such as 100M, 200M, 500M) business, and in some developed areas opening Gigabit business as a leading direction.

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At present, 1G-EPON and GPON have been deployed in China on a large scale. Policy-driven, competition-driven, demand-driven, promote broadband access network to begin to move towards 100 M, Gigabit. In order to meet the needs of users, access technology needs to upgrade to a new generation platform based on 10G rate PON technology. The 10G rate PON technology mainly includes 10G-EPON, XG-PON and XGS-PON.

10G-EPON technology gradually mature

10G-EPON standard is the IEEE802.3av(later being incorporated into IEEE802.3), including 10G / 10G symmetry and 10G / 1G asymmetric two modes. At present,10G-EPON technology and equipment have been very mature.As early as 2011, China Telecom successfully achieved the interoperability of 10G-EPON chip-level and system-level. 10G-EPON device has been scale deployment in FTTB scene, and started the deployment of the FTTH scene.As the cost gap of the symmetry and asymmetric PON port is not large, in order to reduce the type of board, in principle, only the symmetric 10G-EPON port is deployed on the OLT side. As the 10G-EPON port of the OLT can be compatible with three types of ONUs, including 10G / 10G symmetry, 10G / 1G asymmetrical 10G-EPON ONU and 1G / 1G EPON ONU, therefore, ONU can be deployed flexibly according to user needs.

Recently, China Telecom focused on promoting the 10G / 1G EPON uplink wavelength range narrowed. According to IEEE802.3 standard, the uplink wavelength range of 10G / 1G EPON is 1260nm ~ 1360nm. The original intention of this provision is to align with the uplink wavelength range of 1G-EPON, but the biggest problem is to take up the valuable resources of O-band 100nm. China Telecom proposed to narrow the wavelength range to 1260nm ~ 1280nm (shown in Figure 1), that is, consistent with the 10G / 10G EPON uplink wavelength range. In the case of that 10G / 1G EPON FTTH ONU has not yet deployed on a scale, narrowing the uplink wavelength, O-band more wavelength resources will be used for future PON technology, which is of great significance to keep the sustainable development of PON network.

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Figure 1  10G / 1G EPON uplink wavelength range narrowing schematic

Progress and Coexistence of XG-PON Technology

The XG-PON standard is ITU-T G.987 series, which is the downlink 10Gbit / s, uplink 2.5Gbit / s asymmetric mode. At present, XG-PON technology and equipment has matured, especially, after nearly two years of testing, China Telecom successfully implemented XG-PON lab interoperability in 2016, and verified in field trials. Recently, XG-PON will be deployed in FTTH scenarios.

XG-PON deployment needs to focus on solving the problem of coexistence of GPON and XG-PON. As the downlink, uplink and wavelength range of GPON and XG-PON are different, both coexist in wave division. There are two main coexistence programs: the first is to use WDM1r (shown in Figure 2), which is described in the ITU-T standard; the second is the use of GPON / XG-PON dual-mode PON port (optical module) Coexistence, which is innovative program proposed by China Telecom(shown in Figure 3). China Telecom's innovative program is mainly to solve that the introduction of WDMr1 brings about 1.5dB of insertion loss, leading to the problem of tension or shortage of link budget, at the same time the project implementation is also more simple. Overall, these two programs in the introduction of insertion loss on the ODN, the difficulty of upgrading the construction of the project, the difficulty of equipment development, whether to use the original resources and other aspects have its own characteristics(the two coexistence schemes are shown in Table 1),and will have the application scene. At present, the two coexistence methods, in particular, devices based on GPON / XG-PON dual-mode PON ports have been verified by laboratory and field tests.

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Figure 2  GPON and XG-PON using WDM1r coexistence

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Figure 3  GPON and XG-PON Coexistence through the dual-mode PON port (optical module)

Table 1 Comparison of coexistence of GPON and XG-PON

Method One

Method Two

(WDM1r mode)

(Dual-mode PON port mode)

The introduction of insertion loss

WDM1r introduces a loss of about 1.5dB

Do not need independent WDM1r, ODN does not introduce insertion loss

Construction

Engineering construction is more complex, need to disconnect the backbone of fiber, insert WDM1r

The construction is simple and the GPON board is replaced directly into a dual-mode PON board

Development difficulty

Development is relatively simple

Development of Dual mode optical module is more difficult

Resource utilization

The original GPON board can be reused

The original GPON board can not be used (can be moved to other OLT); When XG-PON is dominant in the future, the GPON part of the dual mode optical module is wasted

The dual-mode PON port usually implements two link budget levels, one is GPON Class B + and XG-PON Class N1 integration, the other is GPON Class C + and XG-PON Class N2a integration. Due to the specified link budget value of GPON, XG-PON standard are slightly different (GPON Class B + is 28dB, XG-PON Class N1 is 29dB; GPON Class C + is 32dB, XG-PON Class N2a is 31dB), when both are integrated, it needs to form a unified link budget value. Taking into account the dual-mode PON port to be compatible with the existing network deployed GPON ONU, it should be unified according to the GPON link budget value (shown in Figure 4). China Telecom has proposed two link budget levels for dual-mode PON port Class D1 (28dB) and Class D2 (32dB), and has been adjusted on the basis of ITU-T standard to form specific indicators of optical interface parameters. In addition, it should be noted that the dual-mode PON port indicators involve only the OLT, ONU optical interface indicators have not changed.

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Figure 4 Dual-mode PON port link budget level diagram

XGS-PON Technical progress and deployment strategies

XGS-PON is ITU-T's recently standardized 10Gbit / s symmetric rate PON technology, its standard G.9807.1 released in June 2016.There are two main XGS-PON deployment modes. The first type (shown in Figure 5) is the direct deployment of XGS-PON on the OLT side. This mode can be subdivided into two cases that GPON and XGS-PON coexistence in WDM1r mode, and using GPON / XG-PON / XGS-PON triple-mode PON port supports the coexistence. Since the OLT XGS-PON port is compatible with the XG-PON and XGS-PON ONUs (the OLT supports 10G, 2.5G dual rate reception when the Basic wavelength set is used), the XG-PON port is not required to be deployed on the OLT side. The second (as shown in Figure 6) is the OLT side to XG-PON-based, to meet the main needs of residential users; XGS-PON faces a special scene with high uplink bandwidth requirements(Such as business users, etc.), on-demand deployment, do not consider coexistence with GPON.

Taking into account the different network conditions, different deployment time and other factors, different operators may take a different strategy to deploy XGS-PON.Due to release time of XGS-PON's ITU-T standard is not long, equipment maturity, interoperability has not yet fully verified; at the same time, the recent cost gap between XGS-PON port and XG-PON port of OLT side still can not be neglected, and from the demand point of view, it is mainly for asymmetric bandwidth requirements of residential users. Therefore, model two is appropriate for the recent deployment of XGS-PON.

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(a) GPON and XGS-PON coexist in WDM1r mode

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(b) using the GPON / XG-PON / XGS-PON triple-mode PON port support coexistence

Figure 5  XGS-PON deployment model one

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(a) GPON and XG-PON coexist in WDM1r mode

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(b) GPON and XG-PON coexist with GPON / XG-PON dual mode PON port

Figure 6  XGS-PON deployment model two

PON integration has become an important direction of future

For the future evolution of PON technology, ITU-T has developed NG-PON2 (G.989 series) standards, IEEE 802.3ca task group is developing 100G-EPON (including 25G, 50G, 100G three rates), but "PON fusion" is more worthy of attention. For a long time, ITU-T and IEEE, respectively develop PON standards, the two systems evolve, but the demand is basically the same, which caused a lot of waste in the equipment development, but also increased the complexity of network deployment. PON integration will bring tangible benefits to all aspects of the industry chain, such as operators, equipment manufacturers, chips and device manufacturers. Since the beginning of the discussion in the Broadband Forum in November 2016, as a principle and direction, more and more consensus has been gained in the industry. However, the real realization of PON integration, is a long and complex process. At present, the basic consensus in this aspect is that the standards of the organization's research scope, operating mechanism is difficult to change, PON integration should be achieved through the bottom-up efforts of members of standard organizations.

To promote PON integration, the next step is to work in both technical and technical aspects. Non-technical factors are more important because of the fact that there are two major PON standard systems that are not entirely technical factors. It is necessary to explore the specific mechanisms for effective synergy between different standards organizations, adopt a variety of forms to gradually unite the consensus, eliminate the concerns about the PON integration, and promote the relevant standards organizations in the new standards should be conducive to PON integration. On the technical side, it is necessary to synchronize the deployment time, rate, link budget and coexistence of the next generation PON between ITU-T and IEEE. Simultaneously, focus on analysis and evaluation single wavelength and multi-wavelength, per wavelength rate, fixed or adjustable wavelength and other key issues, and choose the most appropriate technical direction of fusion PON.

As China has become the world's largest PON market, China's operators, manufacturers should promote the PON integration process to play a greater role. In the IEEE 802.3ca conference held in mid-July 2017, based on the joint proposal of Chinese operators and manufacturers and vigorously promoted, the PON integration in the 25G, 50G and 100G EPONs has been widely supported. The standard time schedule has been adjusted for the goal of PON integration, 50G and 100G EPON implementation began to re-argument, PON integration has taken a solid step forward.

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