Fiber to the home (FTTH) is a system which installs optical fiber from a central point directly to individual buildings such as residences, apartments and businesses to provide unprecedented high-speed Internet access. The deployment of FTTH access network has come a long way before subscribers adopt optical fibers instead of copper lines to achieve broadband Internet access. Generally speaking, there are two basic paths to deploy a high-speed FTTH network: passive optical network (PON) and active optical network (AON), which will be elaborated in this post.
PON is a point to multi-point network structure in which unpowered fiber optic splitters are used to separate and collect optical signals. The PON system enables a single optical fiber to serve multiple subscribers without the need to deploy individual fibers between the hub and the end users. A passive optical network does not include electrically powered switching equipment and shares fiber optic strands for portions of the network. Powered equipment is required only at the source and receiving ends of the signal.
In a typical PON system, PLC fiber splitters are the core. A fiber splitter combines multiple optical signals into a single output, or the fiber splitter takes a single optical input and distributes it to multiple separate outputs. These splitters for PON are bi-directional, that is to say, the fiber signals can be sent downstream from the central office, broadcast to all users, and signals from the users can be sent upstream and combined into one fiber to communicate with the central office.
AON is a point-to-point network structure in which each subscriber has their own fibre optic line that is terminated on an optical concentrator. AON covers electrically powered switching equipment, such as a router or a switch aggregator, to manage signal distribution and direction signals to specific customers. The switch directs the incoming and outgoing signals to the proper place by opening and closing in various ways. The reliance of AON on Ethernet technology makes interoperability among vendors easy. Subscribers can select hardware that delivers an appropriate data transmission rate and scale up as their needs increase without the need to restructure the network. However, AON requires at least one switch aggregator for each subscriber.
When choosing between a PON or an AON, it is essential to consider what services are going to be delivered over the network, the overall network topology and who the primary customer will be. The followings are the principal criteria to be considered when deciding between PON and AON.
In an AON system, the subscribers have a dedicated fiber optic strand. That is to say, each subscriber gets the same bandwidth that doesn’t be shared. While the users share the fiber optic strands for a portion of the network in PON. Thus people who use PON may also find that their systems are slower, as all users share the same bandwidth. If something went wrong within a PON system, it would be more difficult to find the source of the problem.
When running an existing network, it’s known that the main source of cost is the maintenance and powering equipment. Since active optical network is powered network, making it more expensive but less reliable than a passive optical network, especially if one is wanting a fully redundant system.
AON can cover a distance range of up to 90 km, while PON is usually limited by fiber cable runs of up to 20 km. This means that the PON subscribers must be geographically closer to the originating signal.
In addition, there are some other factors to consider if it is relevant to special applications or services. For example, radio frequency and video services will be deployed, then a PON is typically the only practical solution. If all services are Internet Protocol-based, however, either a PON or an AON could be appropriate. If there are longer distances involved and providing power and cooling to active components in the field could pose a problem, then a PON may be the best choice. Alternatively, if the target customer is commercial or if the project involves multiple dwelling units, then an AON may be a better fit.
Both PON and AON make up the fiber backbone in FTTH systems that allow people and businesses access to the internet. Whether an operator is deploying PON or AON, all can be accomplished with either home run, centralized split, or distributed split architectures. Many operators deploy a blend of these under different circumstances. However, with the increasing demand for interoperability and scalability for networking, there is a tendency that network architecture would allow any fiber to be used interchangeably in either a PON or AON application as future needs dictate.
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