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.
March/April 2019 I 49
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
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.
2:32
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.
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).
FIGURE 1: An illustration of a POL architecture.
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