What are OLT and ONU?

1.  What is OLT?
OLT means Optical Line Terminal. OLT is used to connect to the optical fiber trunk line. It functions as a switch or router in a traditional communication network. The most important execution functions are traffic scheduling, buffer control, and providing user-oriented passive optical network interfaces and allocating broadband.
Simply, it is to realize two functions. For the upstream, it completes the upstream access of the PON network; for the downstream, it sends the obtained data through the ODN network and distributes it to all ONU user terminal equipment.

1.1 What are the interfaces of the OLT?


Take Baudcom 16 ports GPON OLT as an example.
The EPON OLT has 16*GPON ports for downstream, 4*GE ports for uplink, 4*SFP slots for uplink, 2*SFP+ slots for uplink, 1*USB port.

(1) PON port:
The PON ports are connected to a optical fiber splitter through PON SFP optical module, and each PON port is connected to one optical fiber splitter. If we use 1:64 optical fiber splitter, then one GPON port can be connected to 64 ONU, which means that this 16 ports GPON OLT can connect 1024 ONU. One GPON port can connect up to 128 GPON ONU modem, and one EPON port can connect up to 64 EPON ONU modem. The PON SFP optical module needs to be purchased separately.

(2) Uplink port:
Mainly connected to the Ethernet switch. GE uplink ports connect to the switch with Ethernet cables; and SFP uplink slots connect to the switch with optical fiber cables. The optical SFP module needs to be purchased separately.

(3) Console port:
Centralized network management platform. Network element management, security management and configuration management can be realized on the OLT. It can not only monitor and manage devices and ports, but also enable service provisioning and user status monitoring, and can also allocate broadband according to the QoS/SLA requirements of different users.

2.What is ONU?
ONU means Optical Network Unit, divided into active optical network unit and passive optical network unit.
The network ONU has two functions: selectively receive the broadcast sent by the OLT, and respond to OLT when receiving; collect and cache the Ethernet data that the user needs to send, and send the buffered data to the OLT according to the allocated sending window.
In the FTTx network, under different deployments, ONU access methods are also different, such as FTTC (Fiber To The Curb): ONU is placed in the central computer room of the community; FTTB (Fiber To The Building): ONU is placed in the junction box of the corridor; FTTH (Fiber To The Home): The ONU is placed in the home user. By the way, in the FTTH network, ONU is also called ONT(Optical Network Terminal)

2.1 What are the interfaces of the ONU?

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Take Baudcom dual band wifi GPON ONU as an example.

1.RF/CATV port: connect cable TV
2.Power port
3.USB port: Usually USB 2.0 interface
4.LAN port: FE (10/100BASE-T), GE (10/100/1000BASE-T) optional
5.Phone port: also known as POT, VOIP, Voice, FXS
6.Optical port: connect ODN
7.Antenna: Provide WiFi, 2.4G WiFi or dual band 2.4G/5G WiFi


3. What is the relationship between ONU and OLT?

The OLT is the management terminal, and the ONU is the terminal; the service provisioning of the ONU is issued through the OLT, and the two are in a master-slave relationship. Multiple ONU can be connected to one OLT through an optical fiber splitter.

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4. What is ODN?

ODN is Optical Distribution Network, which is the optical transmission channel between OLT and ONU. The main function is to complete the two-way transmission of optical signals, usually composed of optical fiber cables, optical fiber connectors, optical fiber splitters and supporting equipment for installing and connecting, the most important part of which is the optical fiber splitter.

5. Conclusion
ONU and OLT are indispensable components in the GPON network system. If you are considering to purchase the ONU or OLT devices, you can choose the function and number of ports according to your needs.


Post time: 2023-03-10


Lomoveishiy – Finland

I needed those to connect my PC on the third floor to have internet access in that room, and ISP installed their modem on the first floor only. After dropping fiber patch cables, plugged in all cables into these media converters at both sides, and link came up instantly. Was much easier than I thought!

Raymond – USA

Great experience – units worked straight out of the box – just needed plug in cables and we were done. I also like the possibility to enable jumbo frames, while we do not have a need for this feature at the current moment it’s great to have this option.

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