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
| |
Standard
Originator |
Maximum
Split ratio |
Downstream
Capacity* |
Upstream
Capacity* |
(OSI) Layer 2
encapsulation |
| APON |
FSAN |
1:32 |
622 Mbps |
155 Mbps |
ATM |
| BPON |
FSAN /
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 |
| GPON |
FSAN /
ITU-T G.984 |
1:64 |
2.5 Gbps |
1.25 Gbps |
ATM & Ethernet |
Notes
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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