10G PON Technology Status, Development and Deployment Recommendations
With the deployment and implementation of broadband network fiber optic transformation work, the areas where broadband network fiber optic is realized, the network quality is improved, the failure rate is reduced, and the user’s good feeling of using it rises. At present, the formation of broadband access network is dominated by FTTH, PON + LAN as a complementary network pattern, the future broadband access network if the unified use of PON technology for networking, not only can provide a high-quality user experience, while reducing business operating costs and improving economic efficiency. Next, this paper will combine the business needs and make suggestions on the technical development and deployment of 10G PON.
What is a PON Network?
PON network consists of OLT, ODN and ONU, OLT is located at the core of the network topology, accessing multiple service networks upward and multiple users’ services downward through ODN, and is an important node for service aggregation and distribution. Regardless of the network location or network functions, OLT equipment is the core of the PON network. As more and more services such as Internet access, 4K IPTV video, smart home services, small and medium-sized private lines, IMS voice, mobile backhaul, etc. are carried on PON networks, the demand for bandwidth and the refinement of management are increasing. the development of PON technology and the evolution of OLT equipment deployment play a crucial role in the development of broadband access networks.
Analysis of the Current Situation of PON Network
(1) OLT equipment deployment
The OLT equipment of domestic operators has been deployed since 2006, mainly for PON+DSL access at the beginning, and FTTH has been deployed on a large scale since 2009, which has been more than 10 years since then. The products of manufacturers have 2~3 generations of products running in the existing network according to the slot bandwidth, the switching capacity of the whole machine and the support for PON boards. The main push equipment of manufacturers running in the current network has a single slot switching capacity of 40G/slot, and all support 10G EPON and XG-PON1.
(2) PON technology deployment
With the gradual commercialization of 10G PON technology, the types of PON boards configured in OLT equipment in the existing network are divided into four categories: EPON, GPON, 10G EPON and XG-PON, among which EPON and GPON are the main ones.
EPON was commercially available in domestic operators about 2~3 years before GPON, driven by China Telecom and China Unicom’s efforts to improve the EPON standard, and EPON dominated the construction until 2013, after which GPON gradually took the lead in OLT construction due to its advantages in bandwidth. From the perspective of existing network stock deployment, China Unicom and China Mobile’s OLT equipment is dominated by GPON, while China Telecom is dominated by EPON.
The construction of 10G PON started around 2015. The price of 10G PON ONT is about 5 times higher than the existing EPON/GPON terminals due to the consistently high price of 10G optical modules. In the current environment where operators generally give away terminals to customers, and the service demand is basically below 100Mbit/s, major operators are cautious about the deployment of 10G PON applications. At present, 10G PON is mainly used in 10G PON+ LAN and FTTH deployment. 10G PON+ LAN is mainly used to transform the existing cell LAN network and PON+ LAN network. On the one hand, it solves the problem of insufficient bandwidth caused by the high number of access users; on the other hand, since multiple users share the price of optical modules in the MDU, the overall cost does not increase much compared with the PON+LAN network, so it is used on a large scale, and both 10G PON and XG-PON are technically used. The main purpose of 10G PON FTTH is to promote and verify the products of 10G PON FTTH.
10G PON Technology Development
(1) 10G PON technology development route
IEEE-led EPON and ITU-led GPON have both evolved to 10G PON stage, and the subsequent planning is for 100G PON, there are some differences in the specific evolutionary route, and the corresponding evolutionary route is shown in the figure below.
(2) EPON Technology Evolution
10G EPON symmetric and asymmetric technology standards and products have been perfected, and have the advantage of coexisting with EPON terminals in the same ODN network without adding gyroscopes in the standard. 10G PON optical modules for OLTs have been significantly reduced in price after the centralized procurement in 2016, and operators have started to deploy 10G EPON in advance at the local end considering the future network evolution, and still use EPON ONTs for FTTH construction at the client side. EPON ONTs are used for FTTH construction. At the same time, because the price difference between symmetric mode optical modules and asymmetric mode optical modules is not large, and considering the asymmetric 10G EPON upstream and downstream bandwidth ratio of 1:10, in order to avoid the upgrade demand brought by the subsequent uplink service development, operators prefer to deploy 10G EPON symmetric mode on the OLT side.
(3) GPON Technology Evolution
For 10G GPON standard, the asymmetric XG-PON technology standard and products have been perfected. The fixed-wavelength symmetric 10G GPON standard XGS-PON was released in February 2016, and as the devices involved in this standard are relatively mature, some manufacturers’ products are now available for commercial use. The adjustable wavelength NGPON2 (TWDMPON) standard has been perfected, and OLT products have been commercially available in Europe and the United States, while there are corresponding MDU products for the enterprise private line market. NGPON2 adjustable wavelength optical modules are more expensive and difficult to implement. After the ITU supplemented the symmetric fixed wavelength 10G standard (XGS-PON), some manufacturers believe that NGPON2 may be skipped and evolve directly to the 4×25G 100G PON solution, and may achieve convergence with the 100G EPON standard.
In the short term, the ONT price of 10G PON will not drop to the existing EPON/GPON price range, so it is bound to face the situation of coexistence of 10G PON and user-side EPON/GPON terminals at the local end. The coexistence of GPON and XG-PON terminals in the same ODN network requires the addition of WDM1r modules, which limits the deployment of XG-PON in the existing network. Therefore, there is a Combo PON solution that combines GPON and XGPON optical modules and WDM1r in one optical module. However, the optical module of Combo PON solution can only use XFP package, and only 8 PON ports can be realized on a single board (the conventional way is SFP+ package, and 16 PON ports can be realized on a single board), and the light-emitting power of the optical module is required to be higher due to the insertion loss of WDM1r. At present, it can only realize the light-emitting power of B+/N1, and cannot provide C+/N2a high power module in the short term, which limits the application in long-distance large splitting ratio scenarios.
Development Trend of OLT Equipment
OLT equipment has the following two main trends: first, support for 10G PON boards, including single-slot switching capacity and the entire switching capacity, as well as uplink port support for 10GE and other larger bandwidth ports, etc.; second, with the evolution of the overall network structure of operators to SDN/NFV, OLT equipment itself faces the problem of evolution to SDN/NFV.
(1) Support for 10G PON by existing network equipment
The existing network equipment can support 10G PON board by upgrading the main control board and power supply. After upgrading the equipment, most of the existing network equipment also supports 10G PON. therefore, when the existing network OLT equipment is configured with 10G PON boards, in addition to the support of the equipment itself, each merchant also needs to upgrade the network management and equipment.
(2) Evolution to SDN/NFV
SDN/NFV can share access resources, facilitate business management and realize multi-service bearing. Through SDN/NFVization, the following functions can be achieved: hardware resource independence, VLAN resources, MAC table, routing table, QoS queue resources independent; software features independent, features and functions can be configured differently, differentiated customization; management decentralization and sub-domain, vOLT configuration pipeline isolation, including service issuance, operation and maintenance, alarms, logs, etc.
(3) Next-generation OLT Products
At present, most of the next-generation optical access platforms are based on existing products to achieve the evolution of next-generation 100G access and SDN, and the SDN of OLT equipment is still in the planning stage, so OLT does not have the conditions for SDN in the short term.
10G PON Technology Existing Network Deployment and OLT Evolution Suggestions
(1) 10G PON technology deployment
The current broadband construction is dominated by FTTH, but the construction of 10G PON is still dominated by 10G PON + LAN. The early deployment of FTTH in cities such as North, Guangzhou and Shenzhen, has begun to face the demand for upgrading the original FTTH network. However, due to the factors of few 10G PON ONT terminal types and high prices, 10G PON is still mainly deployed on the OLT side in the short term, and the terminal side still mainly adopts EPON/GPON terminals to increase the support for GE ports and provide Gigabit home services to a small number of users. In the future, with the popularity of high bandwidth users, as well as 10G PON terminal scale and price decline, will gradually promote the scale application of 10G PON FTTH. At present, the scale deployment of 10G EPON in OLT side instead of EPON is already available, and the deployment of XG(S)-PON in OLT is pending the maturity of Combo PON. In addition, simplifying the standard of XG-PON and adopting the same wavelength strategy as 10G EPON to remove WDM1r in ODN network, and sacrificing bandwidth in exchange for coexistence with GPON ONT is also a feasible path, but it needs to promote the revision of XG-PON standard.
For the existing network does not support the 10G PON board manufacturers of equipment should be gradually replaced, the use of user migration to other OLT, the overall replacement of equipment and other ways to gradually achieve the above-mentioned equipment to withdraw from the network.
(2) Related technology deployment suggestions
At present, the PON network has carried a variety of services such as broadband, voice, IPTV live, IPTV on demand and private line, while the PON network carries the network management information of PON equipment and home gateway, and may also carry mobile backhaul and forwarding services in the future. With the increase of service types and the small number of users (generally a dozen to several dozen) accessed under a single PON port, it is decided that the traffic of a single PON port is characterized by strong suddenness and uncertainty. The original way of calculating traffic according to the service model is no longer suitable for the traffic characteristics of PON networks, and the following technical strategies are recommended for PON network deployment to increase network bandwidth and improve user experience.
① Deploy Layer 2 multicast in the access network for IPTV service, including IGMPProxy for OLT and IGMP Snoop-ing for ONU, to minimize the bandwidth consumption of PON ports.
②The broadband access network deploys 802.1p-based Layer 2 QoS technology to prioritize the forwarding of high-priority services when there is local short-term network congestion.
③Home gateways and set-top boxes with built-in soft probes, along with network traffic monitoring and analysis systems (e.g. Huawei uTraffic, ZTE BigDNA, etc.) to achieve dynamic monitoring at the service level and network level.
PON ports that still cannot meet the bandwidth demand through the deployment of the above technical strategies should be expanded and adjusted by adjusting user distribution, reducing split ratio, and upgrading 10G PON.
(3) Adjustment of OLT uplink
The uplink of OLT equipment is gradually adjusted from N×GE to N×10GE according to the traffic demand, while small-capacity OLT access is adopted for users with small number and long distance according to the distribution of OLT, and the unified management of cascaded OLTs is realized through OLT cascading and virtualization. At the same time, the OLT uplink switch should be gradually reduced, and the multi-level cascade switch will increase the network complexity and increase the network latency. Finally, the purpose of improving the bandwidth throughput and enhancing the video service experience of users is achieved.
At present, PON is the main technology to realize FTTH, both in terms of equipment cost, operation and maintenance management, and bandwidth access issues, the deployment and evolution of OLT under PON technology has largely improved the capacity of bandwidth access network, while downgrading the economic cost, achieving more business access, higher bandwidth bearing and more refined management.