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ICT Today March/April 19

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March/April 2019 I 49 2:32 POL OVERVIEW What constitutes a POL? It is a point-to-multipoint fiber architecture that uses passive optical splitters to divide the signal from one optical fiber into multiple fiber branches. The signals are transmitted simultaneously in both directions over separate wavelengths—1310 nm for upstream data and 1490 nm for downstream data in the case of GPON. A POL uses a single piece of centralized active equipment, the optical line terminal (OLT) or central switch. A passive singlemode fiber network runs down to the desktop through an optical splitter and into a thin-client edge device or optical network terminal (ONT) as depicted in Figure 1. It is a fully passive solution, except at the endpoints where the terminal equipment (i.e., OLT and ONT) reside. There are several advantages to this type of technology. First, the POL architecture shifts the network intelligence to a central location (the OLT) while centralizing the management of all ONTs to reduce the complexity of managing and maintaining the network, thereby allowing IT managers full control of network services. Second, because GPON technology uses singlemode optical fiber, rather than multimode optical fiber more commonly deployed in enterprise applications, it can support a span of up to 20 kilometers (km). This means networks can cover much larger span lengths without installing additional power on each floor. Instead, the network uses passive splitters. Not only are the splitters small, but they typically allow an aggregate up to 32 ONTs onto single connections in the central equipment room. This saves space and reduces energy consumption. Security is also not an issue as GPON technology has inherent military-grade encryption. FIGURE 1: An illustration of a POL architecture. 3. Optical Splitter Fully passive equipment, no power consumption Replaces the equipment racks at floor level Small size, can e.g. be installed on false ceiling Typical 1 input for 32 fibre outputs. 1. Central Switch OLT = Optical Line Terminal Installed in the main equipment room of the building. Connects the GPON network to the core network (routers). 5. GPON Terminal Equipment ONT = Optical Network Termination Terminates GPON fibres and provides standard GE connectivity to end-devices. Managed 100% by OLT (Central Switch) Different models possible with different interfaces, e.g. support for Power-Over- Ethernet (POE). Locally powered by default, remote powering as option (with hybrid cable). 2. Vertical Fibre Cabling SMF = Single Mode Fibre Recommended to use pre- connectorized fibres (no splicing) Vertical part can be resillient (2 paths, active-standby) 4. Horizontal Fibre Cabling SMF Typically, 1 fibre for 4 workplaces, replaces 4 long CAT 6A cables. Multiple 1G/10G/100G to core network POL offer several advantages for enterprise LANs: simplicity in design; less equipment and cabling; centralized management; lower energy requirements; ease of testing; and future-proofing.

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