The development of information technology và network shortens the distance between people and makes people increasingly inseparable from the network. PON (Passive Optical Network) technology, mainly composed of OLT, ODN, and ONU, as we all know, tends to mature và has been widely used so far. ONU is usually placed in the user’s trang chủ and varies with the diversity of users’ needs. As for the types of ONU, HGU ONU và SFU ONU are always come into our eyes, but few people can tell the difference between them. What exactly are SFU ONU và HGU ONU? You will get the answer in the rest of the article.

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1.PON System

From the beginning, there is necessary khổng lồ learn about PON as the critical part of ONU. PON (Passive Optical Network) is a kind of single-fiber bidirectional optical access network with a point to lớn multipoint (P2MP) structure with a typical tree-type topology. The system composed of OLT (Optical Line Terminal), ONU (Optical Network Unit), and ODN (Optical Distribution Network) which provides a transmission channel, is what we hotline the PON system.

In the downlink direction (OLT lớn ONU), the signal sent by OLT reaches each ONUs through ODN. While in the uplink direction (from ONU lớn OLT), the signal sent by ONU only reaches OLT, not other ONUs. To avoid data conflict và improve network efficiency, the uplink direction adopts TDMA mode và manages the data transmission of each ONU. ODN provides an optical channel between OLT and ONU. The structure of PON is shown in Figure 1.1.


Figure 1.1 PON Structure for Reference

2.What is ONU?

ONU belongs to lớn the terminal equipment of PON technology, playing an essential role in the PON system. ONU, in between the ODN và user equipment, provides the optical interface & the electrical interface lớn realize the processing, maintenance, và management of various photoelectric signals. There are currently user-side ONU devices, also known as the optical modem, directly installed in home.

The chip core layer, service layer, and public layer consist of the inner part of ONU. The vi xử lý core layer provides multiplexing và optical interface; the service layer mainly refers lớn user port, và the public layer ensures nguồn supply & maintenance management. ONU is divided into active optical network units và passive optical network units. Generally, the equipment with an optical receiver, uplink optical transmitter, and multiple bridge amplifiers is called an optical node. The PON connects to lớn the OLT which connects to the ONU through a single fiber. ONU can access various user terminals, such as set-top box, wireless router, TV, etc., và occupies functions of photoelectric conversion, maintenance, and monitoring.

3.Classification & Application of ONU

According to the application, ONU can be divided into six types, namely SFU (Single Family Unit) ONU, HGU (Home Gateway Unit) ONU, MDU (Multi-Dwelling Unit) ONU, SBU (Single Business Unit) ONU, MTU (Multi-Tenant Unit) ONU and CBU (Cellular Backhaul Unit) ONU. However, only SFU (Single Family Unit) ONU & HGU (Home Gateway Unit) ONU are used by the end-users in practical application.

These two types of ONUs will be introduced in the following.

(1)HGU(Home Gateway Unit)ONU

HGU ONU takes the Virtual Ethernet interface point (VEIP) as the partition point of the OMCI management domain & the non OMCI management domain (TR069, SNMP, etc.) in the data plane. The ME achieves management only through OMCI. The non OMCI management domain can only manage all services và functional modules under the VEIP. Only one VEIP is allowed in each HGU. ONU will report VEIP or PPTP (Physical Path Termination Point) when MIB is uploaded according lớn the type of the device, while HGU can only use & report VEIP rather than PPTP. OLT will judge the type of ONU devices according to lớn the attribution of ONU type in ONU capability. Figure 3.1 shows the service process of HGU ONU.


Figure 3.1 Service Process of HGU ONU

HGU ONU, a trang chủ gateway with an uplink interface of the PON, is designed for the single family unit, which is similar to lớn SFU ONU. Compared to SFU ONU, HGU ONU integrates the functions of ONU và RG to lớn realize more complex control và management and provide Ethernet / IP service, VoIP service, và optional CATV service. HGU ONU has an Ethernet interface and pots interface, và WLAN interface, USB interface, & CATV RF interface are also available. Besides, TR-069 remote management & EMS local & remote management of physical layer and links layer related lớn PON interface are supported by HGU ONU that mainly used in FTTH scenarios.

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Classified by the differences in service processes and interface numbers of ONUs, HGU ONUs has two specific forms shown in table 3-1.

Table 3-1 Specific Forms of HGU ONU

NumberInterface TypeQuantity of Ethernet PortsQuantity of POTS PortQuantity of WLAN PortsQuantity of USB PortsCATV RF Port
HGU-1A1G4 FE2(or 1)1(or 2)1optional
HGU-1B10G/1G4 GE or FE2(or 1)1(or 2)1optional
HGU-2A1G4(or 2)FE2(or 1)00optional
HGU-2B10G/1G4(or 2)GE or FE2(or 1)00optional


PPTP is that OLT directly sends VLAN data lớn each physical interface of ONU, fixing the whole processing process of data flow. VEIP virtualizes the total interface of an ONU. OLT và ONU conduct data docking through VEI. The services under VEIP are managed by ONU through their configuration. In short, PPTP is a LAN port, & VEIP is the virtual WAN port in HGU.

(2)SFU(Single Family Unit)ONU

SFU ONU only supports the OMCI management domain. PPTP is what SFU uses & reports, while VEIP is not available. The processing mode of OMCI configured data flow is different from that of RG flow. For OMCI data flow, there is a one-to-one mapping between the GEM port on the WAN side và the UNI port on the LAN side. All data packets can pass through without MAC address learning or forwarding. Wireless interfaces are not allowed in OMCI. Figure 3.2 shows the service process of SFU ONU.


Figure 3.2 Service Process of SFU ONU

SFU ONU is designed for a single family unit with broadband access terminal function without a more complex trang chủ gateway function from the perspective of application and ONU capacity. SFU ONU, mainly used in FTTH scenarios, has 1 or 4 Ethernet interfaces và is available for Ethernet / IP services, optional VoIP services (built-in IAD), or CATV services.

There are three specific forms of SFU ONU according khổng lồ the difference of service process & interface quantity of ONU shown in Table 3-2.

Table 3-2 Specific Forms of SFU ONU


Interface typeQuantity of Ethernet PortsQuantity of POTS PortsCATV RF Port
SFU-1A1G1 GE or FE0optional
SFU-1B10G/1G1 GE or FE0optional
SFU-2A1G4 FE0optional
SFU-2B10G/1G4 GE or FE0optional
SFU-31G4 FE2optional

Note: SFU is suitable for commercial customers if TDM service is not included.

SFU ONU works under the bridging mode (layer 2 of ISO model), supports multiple VLAN functions, và its Ethernet port can be configured và managed by OLT through OMCI / OAM. Combined with a trang chủ gateway, SFU ONU is good at providing strong service capability. However, SFU ONU does not have a three-layer routing function & WAN connection configuration. The Single port 1GE ONU of C-Data is an exception as it has three-layer routing, static routing, PPPoE, DHCP function, etc.

(3)Functional Differences between HGU ONU và SFU ONU

EPON/GPON StandardIEEE 802.3/802.3ah


IEEE 802.3/802.3ah


Bridging /RoutingBridging/L2Bridging/L2 và Routing/L3
WAN ConfigurationNot supportSupport
TR069 FunctionNot supportSupport
OLT khổng lồ configure its Ethernet PortsSupportNot support
NAT FunctionNot supportSupport
Port Forwarding FunctionNot supportSupport
Loop Detection FunctionSupportNot support
DHCP ServerNot supportSupport
Wireless WIFINot supportSupport

NumberONU FormONU ModelSFU/HGU
1EPON và GPON & XPON 1GE / 1GE + CATVFD511G & FD701G seriesSFU ONU(with routing function)
2EPON và GPON và XPON 1GE + Wi-Fi / 1GE + 1FE + Wi-Fi /

4GE + 2 pots + Wi-Fi (AC)

FD511GW và FD512XW & FD702XW và FD604GW và FD804GW seriesHGU ONU

1GE + 3FE / 1GE + 3FE + CATV / 4GE

FD50X và FD704X & FD504G seriesSFU ONU (without routing function)


Both SFU ONU and HGU ONU have their advantages and disadvantages. The truth is that the main role of ONU is lớn provide end-users with bandwidth access, playing a vital role in the “last mile” of the access network so that kết thúc users can better enjoy the network. Therefore, choosing the right ONU should depend on your network environment.

As a professional ONU supplier, C-Data Shenzhen will focus more on the accumulation & research of technical knowledge to improve our ONU products and meet the customers’ needs for unimpeded network experience. Moreover, C-Data Shenzhen will step further with our customers by improving the chất lượng of products và services without delay.