– Tom Anderson, CommScope’s broadband optical solutions product strategist (http://commscope.com), says:
Service providers continue to face three major challenges in providing broadband services in low-density population areas such as rural communities.
§ They are under pressure from constituents to offer broadband for the “good of the community”—a goal that is clearly critical for the future, maybe even the survival of the community.
§ Operators are answering demands from within their own organizations to increase revenues.
§ At the same time, they are challenged by the relatively higher costs of building a network in rural areas.
Back in April, I posted a blog on how choosing the right fiber architecture contributes to making rural broadband deployments economically feasible. In this posting, I will explain why choosing the right access network technology also can contribute significantly to solving the rural broadband challenge.
There are a variety of fiber-to-the-subscriber technologies from which to choose—Active Ethernet, WDM Systems, RFoG, GPON and EPON. Let’s take a look at each.
Also known as Point-to-Point (P2P) Ethernet, this technology uses a “home run” fiber connection between the subscriber location (home, business or other access point) and the serving office (data center, central office or head end). That means that for every subscriber there is a pair of laser transceivers—one in the serving office and one in the subscriber location. The number of lasers can be described mathematically as 2×, where “×” stands for the number of subscribers. Dedicated lasers and dedicated fiber runs make P2P technology inherently more expensive than, for example, PON technologies; however, it is capable of going longer distances and there is more ability to get high bandwidth to any one point. It is important to note that with fiber technologies the access network is seldom the bandwidth bottleneck in the network, but this is a topic for a future blog posting.
WDM (Wavelength Division Multiplexing) technology for access networks is available, however not often used. It has the same requirement as P2P for 2× lasers with the added complexity of using multiple wavelengths, thus requiring the network operator to have different spares for every wavelength used.
One advantage over P2P is that the fiber network itself can be shared since transmissions are separated by using different wavelengths. Another reason for limited deployment is that WDM PON is not standard. According to the Third WDM-PON Forum Workshop which took place last February in Munich, Germany, WDM-PON might not be standardized before 2020. As with any technology, deploying non-standard systems carries significant risks as the market continues to evolve based on standardized products.
The remaining three technologies—RFoG, EPON and GPON—are all built around a standards-based Passive Optical Network (PON) architecture. With PON, the number of lasers is ×+1 per fiber network, which results from a single laser at the serving office broadcasting to every subscriber on the PON. Of course, each subscriber location has a laser for the upstream communication.
Radio Frequency over Glass is a technology defined by the Society of Cable Telecommunications Engineers that allows for the optical transmission of the RF signals used by cable companies over a traditional PON architecture. It is widely regarded as a transitional technology, bridging the evolution from HFC to PON-based IP networks. It provides advantages for network operators that have an RF headend; however, for service providers lacking an established RF network, the relatively high costs of building the RF serving office makes an IP network more attractive.
GPON (Gigabit Passive Optical Network) is based on International Telecommunications Union’s standards (ITU G.984). Its ×+1 laser count and shared fiber network make GPON a low-cost technology, and its ability to deliver up to gigabit bandwidths to a subscriber means that all but the most demanding commercial subscribers can be served. GPON, like all of the PON technologies, shares bandwidth among the subscribers connected on a single PON. The origin of GPON lies in the telephony industry and is a popular technology with telcos—particularly in North America.
EPON (Ethernet Passive Optical Network), also known as GEPON (Gigabit EPON), offers low ×+1 laser count and a shared fiber infrastructure, just like RFoG and GPON. That drives low equipment costs with up to gigabit bandwidths per subscriber. EPON has been adopted as the technology-of-choice by North American cable operators, with CableLabs developing feature sets for interoperability and provisioning. One interesting consideration that some service providers have taken is to choose EPON in anticipation of interoperation and perhaps leveraging merger/acquisition activity with cable operators.
GPON and EPON are very similar from the perspective of the triple play services they deliver, although there are underlying technology differences that will be explored in a future blog. EPON, GPON and RFoG are the access network technologies often used by rural and low-density service providers to cost-effectively deliver broadband services.
Low cost is critical for broadband in low-density environments. In my last posting we discussed why a distributed tap architecture is the best choice for those network architectures. In this blog I described how RFoG, EPON and GPON technologies all make use of that architecture, deliver bandwidth for today and tomorrow, plus they inherently provide lower cost solutions than Active Ethernet or WDM PON.