Is passive optical networking right for the enterprise?
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Passive optical networking (PON) is a technology used by service providers for fiber-to-the-home topologies. By using a combination of frequency and time division multiplexing, voice, video and data are provided to customers over a single strand of fiber optic cable in an architecture that allows providers to minimize both cabling and equipment.
An optical line terminal (OLT), located at the provider's central office, transmits data to users at 1310 nanometers (nm). The signal passes through splitters and can serve up to 128 customers at a range of approximately 20 kilometers, or 12.5 miles.
Customers are equipped with optical network terminals (ONTs), which provide standard voice (analog), video (coax) and data (Ethernet) services. Upstream data is transmitted at 1490 nm in a time-coordinated fashion so that the ONTs do not interfere with each other when combined. Video services can be provided either by a 1550 nm optical signal or via IP multicast.
Is this technology right for the enterprise? A company or school in a large building or campus environment might reap some of the same benefits as service providers that use PON. By minimizing cabling and equipment, capital and operating expenses can be reduced. A single OLT can serve thousands of customers and can be centralized in a campus environment. ONTs can be placed at the user's work location, such as under a desk or in a hotel or dormitory room, which eliminates the need for active equipment in environmentally controlled telecom closets. This leads to less energy usage, both for the primary IT load and secondary cooling loads. All of this combined can help a building achieve a higher Leadership in Energy and Environmental Design certification.
But there are several factors IT managers must consider before choosing PON. First, the skill set needed to design, deploy and operate PON is substantially different than that needed for a traditional network. The need for analog voice may be minimal in environments where VoIP is provided via other means, such as hard phones, software on laptops or other mobile devices. Unless there is a need for CATV at nearly every work location, then the convergence of broadcast video into a PON environment might not be that beneficial.
Meanwhile, there are standards that define the interface between ONTs and OLTs (both from the International Telecommunication Union with Gigabit Passive Optical Network and IEEE with Ethernet-based Passive Optical Network). The reality is that you may be limited in vendors once you choose your OLT manufacturer. This could lead to vendor lock-in, which may limit procurement negotiations during future expansions, as well as what features you can deploy if your chosen vendor does not implement something you want.
Because PON was originally designed for service providers, PON systems may not have all the features you expect in an enterprise network. Pay particular attention to security features such as 802.1x or power over Ethernet. As PON vendors continue to market their products and services to the enterprise market, however, these features are now being added.
Bottom line: PON is a compelling technology for service providers and it may also be a good choice in some enterprises.
About the author: Andrew Gallo is a Washington, D.C.-based senior information systems engineer and network architect, responsible for design and implementation of the enterprise network for a large university.
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