Understanding OLT, ONU, ODN and ONT - PON Network Structure

                                                                                                                                                                 Shenzhen GigaOpto CO.,Ltd.(2023)

OLT, ONU, ONT and ODN are all components of a Passive Optical Network (PON) structure. A PON is a fiber-optic network that allows several end-users to share a single fiber optic connection.

Here's a brief explanation of each component:

What are Optical Line Terminations ( OLTs )?

An Optical Line Termination (OLT) is a device that is used in Passive Optical Networks (PON) to aggregate and distribute the optical signal to multiple Optical Network Units (ONUs) or Optical Network Terminals (ONTs). The Optical Line Termination (OLT) is typically located in a service provider's central office or data center.

The Optical Line Termination (OLT) plays a crucial role in a PON network by receiving and transmitting data between the service provider's network and the customer's premises. It uses a fiber optic cable to connect to the Optical Distribution Network (ODN), which distributes the optical signal to the Optical Network Units (ONUs) or Optical Network Terminals (ONTs) located at the customer's premises.

The Optical Line Termination (OLT) is responsible for managing the upstream and downstream traffic in the network, including packet forwarding, traffic scheduling, and bandwidth allocation. It also controls the synchronization and timing of the network to ensure that data is transmitted accurately and efficiently.

In addition, the Optical Line Termination (OLT) provides advanced features such as Quality of Service (QoS) and security mechanisms to ensure that the network is reliable and secure. It also allows service providers to remotely monitor and manage the network, enabling them to quickly identify and troubleshoot issues.

Optical Line Termination ( OLT ) equipment contains rack, CSM (Control and Switch Module), ELM (EPON Link Module, PON card), redundancy protection -48V DC power supply modules or one 110/220V AC power supply module, and fans.

Some additional information about Optical Line Termination (OLT):

• Types of Optical Line Termination ( OLT ): There are various types of Optical Line Terminations ( OLTs ) available in the market, including standalone Optical Line Terminations ( OLTs ), modular Optical Line Terminations ( OLTs ), and blade-based Optical Line Terminations ( OLTs ). Standalone Optical Line Terminations ( OLTs ) are single units that can support a limited number of subscribers, while modular Optical Line Terminations ( OLTs ) and blade-based Optical Line Terminations ( OLTs ) are designed to scale and support a larger number of subscribers.
• Optical Line Termination ( OLT ) interfaces: An Optical Line Termination ( OLT ) typically has various types of interfaces, including Ethernet, GPON, and 10G PON interfaces. Ethernet interfaces are used for connecting to IP-based networks, while GPON and 10G PON interfaces are used for connecting to ONUs or ONTs in a PON network.
• Optical Line Termination ( OLT ) management: Optical Line Terminations ( OLTs ) are typically managed using Simple Network Management Protocol (SNMP) or Command Line Interface (CLI) interfaces. SNMP is a network protocol used for managing and monitoring network devices, while CLI is a text-based interface used for configuring and managing network devices.
• Optical Line Termination ( OLT ) redundancy: Redundancy is an important consideration when deploying a PON network. Most Optical Line Terminations ( OLTs )support redundancy features such as dual power supplies, dual control cards, and hot-pluggable components, which ensure high availability and minimize downtime.
• Optical Line Termination ( OLT ) security: Optical Line Terminations ( OLTs ) support various security features such as Access Control Lists (ACLs), Virtual LAN (VLAN) tagging, and encryption protocols such as Advanced Encryption Standard (AES) to ensure the security of the PON network. ACLs are used to control access to the network, while VLAN tagging is used to segment the network and improve security. AES is a widely used encryption protocol that provides strong encryption and ensures the confidentiality of data transmitted over the network.
• Optical Line Termination ( OLT ) performance: OLT performance is an important consideration when deploying a PON network. Optical Line Terminations ( OLTs ) are designed to support high-speed broadband services and must be capable of handling large amounts of traffic. The performance of an Optical Line Termination ( OLT ) is typically measured in terms of its throughput, which is the amount of data that can be transmitted per second.

What are Optical Network Units（ONUs )

The Optical Network Unit（ONU) is a critical component of a PON network, connecting the customer's premises to the service provider's network and enabling multiple customers to share a single fiber optic connection. It supports a wide range of services, including high-speed broadband, voice-over IP, and video streaming, and includes advanced features such as QoS and security mechanisms to ensure that the network is reliable and secure.

The Optical Network Unit（ONU) has two functions: selectively receive the broadcast sent by the Optical Line Termination ( OLT ), and respond to the Optical Line Termination ( OLT ) if it needs to receive the data; collect and cache the Ethernet data that the user needs to send, and send it to the OLT according to the assigned sending window Send the cached data.

Different deployments of FTTx networks have different Optical Network Unit（ONU) access methods. For example, 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 Curb): To The Home): The ONU is placed in the home user.

Some of the key features of an ONU are:

• Upstream and downstream data transmission: The Optical Network Unit（ONU) is responsible for transmitting data upstream to the service provider's network and downstream to the customer's equipment.
• Optical signal conversion: The Optical Network Unit（ONU) converts the optical signal received from the Optical Distribution Network (ODN) into an electrical signal that can be used by the customer's equipment.
• Service support: The Optical Network Unit（ONU) supports a wide range of services such as high-speed broadband, voice-over IP, and video streaming, allowing customers to access a variety of services using a single fiber optic connection.
• Quality of Service (QoS): The Optical Network Unit（ONU) includes QoS mechanisms that prioritize and manage network traffic to ensure that critical applications receive the necessary bandwidth and network resources.
• Security: The Optical Network Unit（ONU) includes security features such as Access Control Lists (ACLs), Virtual LAN (VLAN) tagging, and encryption protocols to ensure the security of the network.
• Management: The Optical Network Unit（ONU) can be managed remotely by the service provider using Simple Network Management Protocol (SNMP) or Command Line Interface (CLI) interfaces, allowing them to monitor and manage the network and quickly identify and troubleshoot any issues.

What are Optical Distribution Networks (ODNs)

ODN is Optical Distribution Network, which is the optical transmission physical channel between OLT and ONU. The supporting equipment of the device is composed, the most important part of which is the optical splitter.

The ODN plays a crucial role in a PON network by distributing the optical signal from the OLT to the ONUs or ONTs, enabling multiple customers to share a single fiber optic connection. The ODN uses passive components such as splitters, which divide the optical signal into multiple paths, allowing it to be distributed to multiple ONUs or ONTs.

The ODN is designed to be passive, meaning that it does not require any power or active components to operate. This makes the ODN cost-effective and reliable, as it has fewer points of failure and requires less maintenance than active networks.

Some of the key features of an ODN are:

• Fiber optic cables: The Optical Distribution Network (ODN) uses fiber optic cables to transmit the optical signal between the OLT and the ONUs or ONTs. These cables are designed to be durable and reliable, ensuring that the optical signal is transmitted accurately and efficiently.
• Splitters: Splitters are passive components used in the Optical Distribution Network (ODN) to divide the optical signal into multiple paths, allowing it to be distributed to multiple ONUs or ONTs.Splitters are available in various ratios, such as 1:2, 1:4, 1:8, and 1:16, which determine the number of paths that the optical signal can be divided into.
• Connectors: Connectors are used to connect the fiber optic cables and splitters in the Optical Distribution Network (ODN). They are designed to be durable and reliable, ensuring that the optical signal is transmitted accurately and efficiently.
• Optical attenuators: Optical attenuators are used in the Optical Distribution Network (ODN) to reduce the power of the optical signal, ensuring that it is transmitted at the correct level to the ONUs or ONTs. This helps to prevent signal distortion and ensures that the network is reliable and efficient.
• Network design: The Optical Distribution Network (ODN) is designed to be scalable, allowing it to be extended as the number of subscribers increases. The design of the ODN is critical to the performance of the network, as it determines the maximum distance that the optical signal can be transmitted and the number of subscribers that can be supported.

What are Optical Network Terminals (ONTs)

Basically, ONU and ONT are the same devices. Belong to different standard bodies, they both refer to the user side equipment in the GEPON system. In practice, they have a little difference, ONT is located at the customer premise, and ONU is located outside the home. ONU can be working on different temperatures and weather conditions. It should resist water, winds and vandals. The ONU usually communicates with an optical network terminal (ONT), which may be a separate box that connects the PON to TV sets, telephones, computers, or a wireless router.

Some key features of an ONT are:

• Upstream and downstream data transmission: The Optical Network Terminal (ONT) is responsible for transmitting data upstream to the service provider's network and downstream to the customer's equipment.
• Optical signal conversion: The Optical Network Terminal (ONT) converts the optical signal received from the Optical Distribution Network (ODN) into an electrical signal that can be used by the customer's equipment.
• Service support: The Optical Network Terminal (ONT) supports a wide range of services such as high-speed broadband, voice over IP, and video streaming, allowing customers to access a variety of services using a single fiber optic connection.
• Quality of Service (QoS): The Optical Network Terminal (ONT) includes QoS mechanisms that prioritize and manage network traffic to ensure that critical applications receive the necessary bandwidth and network resources.
• Security: The Optical Network Terminal (ONT) includes security features such as Access Control Lists (ACLs), Virtual LAN (VLAN) tagging, and encryption protocols to ensure the security of the network.
• Management: The Optical Network Terminal (ONT) can be managed remotely by the service provider using Simple Network Management Protocol (SNMP) or Command Line Interface (CLI) interfaces, allowing them to monitor and manage the network and quickly identify and troubleshoot any issues.

Conclusion:

OLT, ONU, ONT and ODN are the main components in a PON system, which have been widely used in FTTH applications. The reduced cabling infrastructure (no active elements) and flexible media transmission contribute to the passive optical networks more ideal for home Internet, voice, and video applications. Additionally, passive optical networks can also be applied in college campuses and business environments, providing cost-effective solutions. As PON technology has continued to improve, the potential applications have expanded as well.