High-bandwidth services have been undergoing explosive growth in recent years. Not only new home broadband services like 4K/8K TV, smart home, interactive video, cloud gaming, distance education, livestreaming, and home office are are gaining popularity, but emerging enterprise services such as cloudification, industrial Internet, and smart city/community/campus are also developing rapidly. The expansion of services calls for continuous bandwidth improvement, accelerating the upgrade of access technology from gigabit passive optical network (GPON) to 10G GPON.
Among the 10G GPON standards, 10-gigabit-capable passive optical network (XG-PON), which provides asymmetric rates that reach 10 Gbps downstream and 2.5 Gbps upstream, was the first to complete standardization. The high downstream rates delivered by XG-PON meets the bandwidth requirements of new services like big video, making the technology instantly win operator recognition and promptly start commercial deployment. To protect network investments, a way must be found for XG-PON to be compatible with existing GPON optical network units (ONUs) while allowing for smooth evolution and on-demand upgrades. ZTE did exactly that by launching the industry's first Combo PON solution to implement both XG-PON and GPON. This two-rate Combo PON solution has found popularity with operators by virtue of its good compatibility and great ease of use. It has become the primary solution for 10G GPON construction, and has been put into large-scale commercial use.
As more bandwidth-hungry services, especially new enterprise offerings, fast grow in popularity, the asymmetric XG-PON technology is increasingly not up to the task. Against this background, 10-gigabit-capable symmetric passive optical network (XGS-PON), which offers 10 Gbps bandwidth both upstream and downstream, is gradually becoming the technology of choice for 10G GPON deployment. Although the XGS-PON technology has matured, it still faces the problem of compatibility with a large number of in-service XG-PON and GPON ONUs when the network evolves to XGS-PON. To solve this problem, ZTE took the lead to release a three-rate Combo PON solution to combine XGS-PON and GPON and enable smooth evolution from GPON to XGS-PON.
Technical Implementation
The Combo PON solution integrating XGS-PON, XG-PON and GPON is a built-in optical multiplexing scheme that supports the coexistence of XGS-PON, XG-PON and GPON ONUs (Fig. 1). Also called "three-rate Combo PON", the solution is recognized in the industry as the best path for smooth upgrade from GPON to XGS-PON.
Because XGS-PON and GPON use different wavelengths, three-rate Combo PON multiplexes the two types of wavelengths in an optical module, thereby achieving separate transmission and reception of GPON and XGS-PON signals. The three-rate Combo PON optical module has an embedded multiplexer, called the WDM1r, to combine and divide the four upstream and downstream wavelengths needed by XGS-PON and GPON. XGS-PON uses the 1270 nm upstream wavelength and 1577 nm downstream wavelength, while GPON uses the 1310 nm upstream wavelength and 1490 nm downstream wavelength. The three-rate Combo PON optical module implements the transmission of four wavelengths over a single fiber. Meanwhile, because XGS-PON and XG-PON use the same wavelengths, XGS-PON is naturally compatible with XG-PON ONUs, which results in the coexistence of XGS-PON, XG-PON and GPON.
Leading the Trend in 10G GPON Deployment
Three-rate Combo PON can connect XGS-PON, XG-PON and GPON ONUs, allowing operators to meet the requirements of different customers. XGS-PON ONUs can offer dedicated-line access for enterprise users, XG-PON ONUs can provide gigabit access for home users, and GPON ONUs can deliver megabit access for home users.
Three-rate Combo PON has the following advantages over the PON solution using an external optical multiplexer:
—The optical distribution network (ODN) does not need to be adjusted, so deployment of the three-rate Combo PON solution is quite easy. The external multiplexer scheme means that a stand-alone multiplexer device needs to be installed and the ODN has to be greatly adjusted, which would cause considerable engineering difficulties. By contrast, because three-rate Combo PON employs an embedded multiplexer, compatibility with the in-service GPON ONUs does not require adjustments to the ODN, making the solution easy to deploy.
—No new insertion loss is introduced, thus completely solving the issue of optical power margin. An external multiplexer adds 1–1.5 dB insertion loss, which will strain the already tight optical power budget of many existing networks and make the new multiplexer unfeasible. Three-rate Combo PON does not cause extra insertion loss. Using a same-class optical module, the solution does not change the optical power budget margin of the ODN.
—Equipment room space is saved and network O&M is simplified. Since the optical module of three-rate Combo PON integrates XGS-PON/XG-PON/GPON and WDM1r functions, it eliminates the need for additional equipment. As a result, no extra room space is required and O&M complexity is reduced.
—Interconnection between the element management system (EMS) and operation support system (OSS) is easy, the service provisioning process keeps unchanged, and service migration is fast. Three-rate Combo PON operates in wavelength division mode. The XG(S)-PON and GPON channels automatically match their ONU types, and can use the existing mode of interconnection between XGS-PON/GPON and the OSS. The service provisioning process is unchanged and services are easy to migrate.
In a new-build scenario, using the three-rate Combo PON solution can greatly reduce the initial costs and shorten the investment return period. At the initial stage when the bandwidth requirements are low, the operator can deploy GPON ONUs for common users and 10G GPON ONUs for high-end users. As services grow, the GPON ONUs may no longer meet user demand and the operator can replace them with 10G GPON ONUs. This approach of on-demand upgrading and smooth evolution can achieve a balance between investment and income within a short period of time.
The three-rate Combo PON solution has attracted high attention from top-tier operators in the world. ZTE is actively participating in the three-rate Combo PON tests and commercial trials with operators, leading the trend in 10G GPON deployment.
In China, 10G GPON deployment is in full swing. Recognizing that three-rate Combo PON enables smooth evolution and is compatible with a large number of existing GPON ONUs and XG-PON ONUs, the three major Chinese operators have started wide-scale deployment of the solution. Internationally, three-rate Combo PON has also been highly concerned by operators seeking to carry out bandwidth acceleration and fiber transformation. Incumbents, alternative carriers, and multiple system operators (MSOs) are all actively exploring the application of the solution by conducting tests and deployments. Based on the solution, ZTE has helped leading MSOs deploy their fiber-to-the-home (FTTH) networks.
ZTE's Combo PON solutions have been successfully installed in many countries to assist operators in building gigabit networks. With constant technology innovation, ZTE will continue to create high-quality products to help partners seize market opportunities and obtain competitive advantages.
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