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Internet Access Guide : Fiber-To-The-Home (FTTH)

A PON consists of OLTs (Optical Line Terminals) at the CO side, passive splitters in the distribution network, and an ONU (Optical Network Unit) or ONT (Optical Network Terminal) at each subscriber home. OLT is a line card which has several optical ports. As its name implies, the splitter divides the fiber into several branches directed toward subscriber homes. The (maximum) split ratio is usually 1:32 or 1:64. In real life network, the number of splits are decided based on the bandwidth cap (SLA) for each subscriber in a cluster.

An ONU is used to distribute services to MDU (Multiple Dwelling Unit) or MTU (Multiple Tenant Unit) while an ONT is used to serve a single-family home. ONT is an outdoor unit that serves as a demarcation point between a FTTH operator's network and a subscriber home. Recently, some vendors also offer indoor ONT, the size of DSL/cable modem.

The ONT may have these interfaces: RJ-11 for POTS/VoIP and RJ-45 for Internet, set top box, and/or T1/E1/T3/E3. A FTTH service provider may give an Internet router to each subscriber to enable network monitoring and provide bundled services portal. The distribution of services in a subscriber home may be left to each subscriber or done by the service provider technician as an additional service. Cat 5e cable is commonly used to distribute triple play services throughout the home, but existing coaxial cable installation for distributing cable TV service and power lines are considered as alternatives for in-home distribution network. And don't worry about getting unwired, you can still hook up your Wi-Fi access point to your home backbone network.

There are different types of PON, as follows

Split ratio
(OSI) Layer 2
APON FSAN 1:32 622 Mbps 155 Mbps ATM
ITU-T G.983
1:32 1.25 Gbps 622 Mbps ATM
EPON IEEE 802.3ah 1:32 1.25 Gbps 1.25 Gbps Ethernet
ITU-T G.984
1:64 2.5 Gbps 1.25 Gbps ATM & Ethernet

APON : Asynchronous Transfer Mode (ATM) PON
BPON : Broadband PON
EPON : Ethernet PON
GPON : Gigabit PON
FSAN : Full Service Access Network group of big telcos
(*) before being divided by the number of splits

The most widely deployed PON architecture is BPON, but in the coming years GPON or G-EPON may become the main choice as demand for higher speed connectivity never stops.

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