Internet service providers are always on the lookout for ways to serve more customers at lower cost while maximizing the use of networking resources. But given the cutthroat competition in the telecom market, no one wants to invest in deploying more network infrastructure than absolutely necessary, even with the surge in mobile data communications. That’s why the IEEE 802.3 Working Group, responsible for the development of the Ethernet, is continuously relying on its old friend—optical fiber—and adapting it to provide longer reach and higher capacity along with the ability to aggregate more subscribers onto a single trunk fiber.
The IEEE 802.3 group now has a dedicated task force (IEEE P802.3bk) to extend the range of Ethernet passive optical networks (or EPONs, for short). EPON is an access architecture that carries Internet traffic over an optical fiber network from a central office to multiple users without requiring electric power or any great changes in the outside plant. The idea behind the IEEE P802.3bk project is to serve more subscribers in both urban and rural areas while remaining backward-compatible with what is already deployed.
“Service providers taking advantage of EPON technology will be able to reach farther out and provide services to users even in remote areas, something now not possible using PON solutions,” says Marek Hajduczenia, chair of the task force.
The IEEE P802.3bk project is focused on developing a standard to be called “Ethernet Amendment: Physical Layer Specifications and Management Parameters for Extended Ethernet Passive Optical Networks.” One goal is to extend EPON’s split ratio for a single fiber to subscribers to at least 1:64 at a distance of at least 20 kilometers from the central office. At present, the supported split ratio is 1:32 at that distance. What’s more, Hajduczenia says, it will be possible with careful engineering in the outside plant to have a 32-fiber split at 30 km and a 16-fiber split at 40 km from the central office. Such splits are achieved by supporting new and higher optical power budgets, which define the amount of light transported over a fiber. The higher budget translates directly into the sharing of a single optical port at the central office among a larger number of connected customers, increasing the reach of the network, or both, depending on the deployment model.
“What the IEEE P802.3bk project does is guarantee that today’s investment in the outside plant can be fully reused if more customers need to be connected to a given network port,” Hajduczenia says. “The power budgets newly added to 1G-EPON (1 gigabit per second) and 10G-EPON (10 gigabit per second) systems will make it economically feasible to double the number of connected customers at equivalent distances without having to reengineer the outside plant or add more distribution fibers. The latter is critical for service providers with limited dark fiber capacity.”
EPON is inherently Ethernet. The vast majority of today’s data is created and passed through Ethernet ports on laptops, PCs, or other consumer or business equipment. Moving across the Internet, the data ends up once again in an Ethernet port, having traversed a number of data links of various types, mostly of Ethernet technology. Ethernet, after more than 40 years’ worth of development, is now ubiquitous, with more than 2 billion ports deployed worldwide. More than 85 percent of all installed network connections and more than 95 percent of all local area networks (LANs) are Ethernet-based, making it the most widely deployed type of wireline network technology in the history of telecommunications.
EPON shares the cost-effectiveness of the Ethernet technology that’s already out there, minimizing the number of protocol conversions required to deliver data from an access subscriber into the wider network and back. Furthermore, EPON is simple and reliable, and defines the bare minimum required to do the job: deliver packets between interfaces in the access network. This is something network operators have learned to appreciate in Ethernet technology.
Finally, EPON relies on a rich ecosystem of companies, including silicon vendors, original equipment manufacturers, system integrators, research institutes, and operators—both traditional operators migrating from different versions of digital subscriber line technology to fiber and multiple system operators (MSOs) migrating from hybrid fiber cable (HFC) networks to EPON. The strength of EPON remains in its open character, adaptability, and international coverage, as well as the standardization of aspects of the technology that affect interoperability between devices from different vendors.
EPON is being embraced not only by traditional phone companies but also increasingly by cable operators, specifically in North America, where the companies are providing triple- and quad-play services over their next-generation access networks. MSOs today already have fiber-deep access architectures, where analog fiber transmits signals to and from a fiber node placed relatively close to the customer. But analog fiber in these HFC setups and the fact that the last few hundred meters are served with a coaxial distribution network place a number of limits on bandwidth and services.
To mitigate these restrictions and move toward fiber-deeper deployment, where fiber is delivered as close to each subscriber as is economically feasible (often known as fiber to the home and fiber to the curb, or FTTH/FTTC), a number of MSOs in conjunction with CableLabs, the R&D consortium of cable TV companies, and a group of EPON equipment vendors have developed a set of DOCSIS provisioning of EPON (DPoE) specifications.
These specifications combine two field-proven and highly successful access technologies: EPON and Data Over Cable Service Interface Specification (DOCSIS). Both of these have millions of ports deployed around the world. DOCSIS also brings in mature service-provisioning mechanisms, based on centralized, back-office automation. And EPON provides a highly reliable transport layer between the DPoE system and a number of connected, DPoE optical network units (ONUs), or D-ONUs for short.
EPON also provides extended reach (20 km or more) as well as ultrahigh density at the hub, or head end. The completely passive interconnection structure of EPON reduces both capital and operational expenditures. To make EPON appear as a DOCSIS network to existing operations and support systems, DOCSIS mediation middleware is added to translate between EPON and DOCSIS control signaling.
DPoE embraces the existing published and future extensions (developed under the IEEE P802.3bk project) to the EPON physical layer specifications, reusing them rather than reinventing the transport layer mechanisms. This further demonstrates the open character and adaptability of EPON technology, which can be simply reused in its current definition to serve the distinct requirements of the MSO community. More details can be found in the IEEE Xplore Digital Library.
POWER UTILITIES, TOO
EPONs are also being embraced by power utilities moving toward the smart grid. In particular, they’re applied in the control of power meters remotely from a central management system. There’s enough excess bandwidth so the local power utility could become a telecommunications service provider and offer triple- or quadruple-play services. The first trials of EPON-based smart grids have been very successful in China. In the smart grid application, the longer reach and/or extended split ratio provided by the IEEE P802.3bk project will be critical for cost-effective deployment for new entrants in this space.