ONU vs ONT
The main application types of broadband optical fiber access include FTTH, FTTO, and FTTB, and the forms of user side devices vary depending on the application type. The user side device in FTTH or FTTO is used by a single user, called ONT (Optical Network Terminal), and the user side device in FTTB is shared by multiple users, called ONU (Optical Network Unit).

Types of ONT
ONT also know as optical modem, and it is divided into SFU (Single Family Unit), HGU (Home Gateway Unit) and SBU (Single Business Unit).

SFU usually has 1 to 4 Ethernet interfaces, 1 to 2 telephone interfaces, and some models also have cable television interfaces. SFU does not have a home gateway function, and requires a terminal connected through an Ethernet port to dial up for internet access. The remote management function is weak. The optical modem used in the early days of FTTH belongs to SFU, but it is rarely used now.

HGU
1.The HGU is a gateway device, which is convenient for home networking. While the SFU is a transparent transmission device without gateway capabilities, and generally requires the cooperation of a gateway device such as a home router when building a home network.
2.HGU supports routing mode and has NAT function. It is a three layer device; while SFU only supports two layer bridge mode, which is equivalent to a two layer switch.
3.HGU can implement its own broadband dial-up application, and the connected computers and mobile terminals can directly access the Internet without dialing. While SFU must be dialed by a terminal such as the user's computer or mobile phone, or dialed through a home router.
4.HGU is much easier for large-scale operation and maintenance management
5.HGU usually comes with wifi and has a USB port.

SBU
SBU is mainly used for FTTO user access, and generally has an Ethernet interface. Some models have an E1 interface, a fixed telephone interface, or a wifi function. Compared with SFU and HGU, SBU has a better electrical protection performance and higher stability, and is also commonly used in outdoor situations such as video surveillance.

Types of ONU
ONU is divided into MDU (Multi-Dwelling Unit) and MTU (Multi-Tenant Unit)
MDU is mainly used for the access of multiple residential users under the FTTB application type, and generally has at least 4 user side interfaces, usually with 8, 16, 24 FE or FE+POTS (fixed telephone) interfaces.

MTU is mainly used for the access of multiple enterprise users or multiple terminals within a same enterprise in the FTTB scenario. In addition to Ethernet interface and fixed telephone interface, it may also have E1 interface. The appearance and function of MTU are usually not the same as those of MDU, but they have better electrical protection performance and higher stability. With the popularization of FTTO, the application scenarios of MTU are getting smaller and smaller.

Broadband optical fiber access mainly uses PON technology. When the specific form of user side equipment is not distinguished, the PON system of user side equipment can be collectively called as ONU.

Composition of PON System
ONU, ONT, SFU, and HGU describe user side devices for broadband access from different perspectives.

Relationship Between Broadband Access Devices