Nobody knows the extent to which broadband speeds will continue to increase over the next 5-10 years, but service providers intend to be certain that their network solutions will be able to handle whatever is coming. With the announcement of the 10G Platform the cable industry has set a new target for future broadband speeds of at least 10 Gbps, with symmetry being a key component of that new speed target.
Whereas the majority of the cable industry continues to leverage their ubiquitous hybrid fiber coaxial (HFC) networks to provide high-speed data services to a large proportion of their subscribers, fiber to the home (FTTH) solutions that utilize passive optical networks (PON) remain an important component of their solution set. Thus, it is important for FTTH technology to continually evolve in a way that meets future bandwidth demand. I am pleased to announce PON solutions have reached a new milestone in that technology evolution with the recent approval by the Institute of Electrical and Electronics Engineers (IEEE) of the 25G/50G-EPON standard.
Key Features of 25G/50G-EPON
A key requirement for 25G/50G- EPON is it must operate over already-deployed PON infrastructure with the same split ratio and nominal 20km reach as previous generations of technology. Beyond an increase is peak capacity, there are many new features and capabilities built into this standard, some of these features are focused on the efficient use of the available capacity and reducing overhead of the media access control (MAC), while others are focused on coexisting with legacy technologies and low-cost implementations. I will focus on just a few of these enhancements to the standard.
- Peak Capacity: As the name implies, the new EPON standard developed by the IEEE 802.3ca Task Force allows for symmetric or asymmetric operation with downstream speeds of 25 Gbps or 50 Gbps, and upstream speeds of 10 Gbps, 25 Gbps, or 50 Gbps. These peak capacities are more than capable of meeting the 10 Gbps symmetric service tier goals set forth in the 10G Platform. Achieving this increase in capacity is accomplished in two ways: (1) expanding the transmission rate to 25 Gbps per wavelength and (2) leveraging wavelength division multiplexing technology to add an additional wavelength. A benefit of this architecture is that service providers can initially deploy a single wavelength providing 25 Gbps, and then add a second wavelength to bring the total to 50 Gbps upon demand.
- Coexistence: An important consideration for service providers is the ability to support coexistence with legacy PON technologies, specifically 10 Gbps PON. Briefly, coexistence enables reuse of existing PON infrastructure by easily adding additional capacity while avoiding the complete removal of legacy PON technology. For 25G/50G-EPON, service providers who have already deployed 10G PON solutions are able to add one or more 25 Gbps wavelengths to bring total capacity to 35 Gbps or 60 Gbps in total over the same PON infrastructure. Various coexistence scenarios are shown in the diagram below.
- Low-Cost Implementation: The economics of any residential broadband solution are always an important consideration for service providers. For optical solutions such as PON, the optical transceiver on each end of the link is one of the more costly components. Particularly for FTTH PON solutions, it is critical to keep costs as low as possible for the customer premise equipment, the optical network unit (ONU) in the case of EPON. In this regard, 25G/50G-EPON aggressively strives to keep ONU optical component costs low in two key ways: (1) fixed wavelengths, instead of tunable wavelengths, and (2) wideband optics in O-band without dispersion compensation. In fact, in greenfield deployments, e.g. new FTTH builds unburdened with legacy PON technology, a 50 Gbps ONU can use two wideband channel sources to reduce costs instead of two narrowband channel sources or operating 50 Gbps on a single wavelength, as shown in the lower portion of the figure above.
Speed, coexistence and low-cost implementations are only three of the outstanding benefits built into the next generation of EPON. Without a doubt this version of PON technology represents the lowest cost per bit compared with any other PON technology. If you are interested in looking for future activities at CableLabs related to integration of this technology into cable networks or discovering more details about 25G/50G-EPON, please feel free to contact us to receive more information.
