What is Passive Optical Network (PON) and GPON？How does It Work?

Passive Optical Network (PON) technology delivers high-speed, reliable, and cost-effective broadband access. Among its types, Gigabit PON (GPON) is widely used for providing gigabit-level bandwidth to meet modern connectivity needs.

Asterfusion’s GPON solution combines GPON OLT SFP modules with SONiC-based open switches, creating a flexible, scalable, and cost-efficient all-optical access network that can be centrally managed through an OpenWiFi-compatible controller—making it ideal for campuses and small-to-medium enterprises seeking simplified deployment and unified control.

For more: Asterfusion’s GPON solution

What is Passive Optical Network (PON) Technology ?

A Passive Optical Network (PON) is a fiber-based broadband access technology designed to deliver high-speed internet, voice, and video services to end users. The key feature of PON is its “passive” nature—there are no powered electronic devices (such as amplifiers or switches) in the transmission path. Instead, it relies on passive optical components, such as splitters, to distribute and aggregate signals. This design results in low power consumption, high reliability, and reduced maintenance costs, making PON ideal for large-scale deployments.

Core Components

1. OLT (Optical Line Terminal)

• Location: Typically installed in the service provider’s central office or data center.
• Functions:
  • Converts data from the internet into optical signals for transmission over fiber.
  • Receives optical signals from end users and converts them back into electrical signals.
  • Manages upstream and downstream traffic across the entire PON network.
• Analogy: Acts as the “central hub” or “brain” of the PON system.

2. ODN (Optical Distribution Network)

• Composition: A network of optical fibers, optical splitters, and connectors.
• Functions:
  • Distributes optical signals from the OLT to multiple end users.
  • Aggregates signals from users back to the OLT.
• Key Feature:
  • Completely passive—no external power required, relying solely on light propagation in the fiber.
  • Common split ratios include 1:8, 1:16, 1:32, and 1:64.
• Analogy: Similar to a municipal water distribution system that channels supply from a main pipe to individual households.

3. ONU / ONT (Optical Network Unit / Optical Network Terminal)

• Location:
  • ONU: Installed in shared spaces such as building equipment rooms, serving multiple users.
  • ONT: Located inside homes or offices, dedicated to a single user.
• Functions:
  • Converts optical signals into electrical Ethernet signals for end devices.
  • Enables computers, routers, phones, and TVs to directly access the network.
• Analogy: Comparable to a household “faucet” that delivers water from the municipal system for immediate use.

Why We Need Passive Optical Networks (PON)?

Passive Optical Networks (PON) were developed to solve the “last mile” problem—delivering high-speed internet from the provider to homes and businesses in a faster, cheaper, and more reliable way.

1. The Old “Last Mile” was Inefficient：Copper, DSL, and coaxial cables suffered from speed loss over distance, frequent maintenance issues, and costly per-home wiring. A better, scalable solution was needed.

2. Fiber Became Affordable: Falling fiber costs and advances in optical modules and splitters made fiber-to-the-home (FTTH) economically viable—just as demand for HD video, AI, and cloud services surged.

3. Passive Beats Active in Reliability ：Active networks require powered devices in the field, which consume energy, complicate installation, and fail during outages. PON uses unpowered splitters, cutting costs and boosting reliability.

4. One Fiber, Many Users：A single PON trunk can serve 32–64 users, reducing cable needs, lowering construction costs, and simplifying maintenance for providers.

In short: PON delivers more bandwidth, better reliability, and lower costs—driven by advances in technology, rising user demand, and the need for operational efficiency.

How does PON Work ?

PON adopts a Point-to-Multipoint topology, distributing signals from a single optical fiber to multiple user endpoints through an optical splitter. Its working principle can be divided into two directions: downstream transmission and upstream transmission:

Downstream Transmission (OLT to ONU/ONT)

• Broadcast Mode: The OLT sends optical signals through the fiber, which are distributed to all connected ONU/ONTs via an optical splitter (typically with a splitting ratio of 1:8, 1:16, 1:32, or 1:64).
• Data Encapsulation: Downstream data is broadcast as optical signals, containing packet data for all users, with each packet carrying an identifier (e.g., VLAN tags or GPON’s GEM Port-ID).
• Signal Filtering: Each ONU/ONT extracts its own data based on the packet identifiers, discarding irrelevant data.
• Wavelength: Downstream transmission typically uses a 1490nm wavelength (GPON standard) to avoid interference with upstream signals.

Upstream Transmission (ONU/ONT to OLT)

• Time Division Multiple Access (TDMA): Since multiple ONU/ONTs share the same fiber for upstream transmission, PON employs a TDMA mechanism to prevent signal collisions. The OLT assigns specific time slots to each ONU/ONT, ensuring orderly upstream data transmission.
• Dynamic Bandwidth Allocation (DBA): The OLT dynamically allocates upstream time slots based on user demand, optimizing bandwidth utilization. For example, high-priority users (e.g., video streaming) may receive more time slots.
• Wavelength: Upstream transmission typically uses a 1310nm wavelength, distinct from the downstream signal.
• Synchronization and Control: The OLT coordinates upstream transmission from ONU/ONTs using control signaling (e.g., GPON’s PLOAM messages or EPON’s MPCP protocol), ensuring time synchronization and data integrity.

Wavelength Division Multiplexing (WDM)

PON achieves bidirectional communication over a single fiber using WDM technology:

• Downstream and upstream signals use different wavelengths (e.g., 1490nm for downstream and 1310nm for upstream), separated by WDM filters.
• Some advanced PON systems (e.g., NG-PON2) employ multiple wavelengths (TWDM) to further increase bandwidth.

Main Types and Differences of PON

Technology	Description	Standard
GPON (Gigabit PON)	Gigabit Passive Optical Network, offering 2.488 Gbps downstream and 1.244 Gbps upstream. Widely used in FTTH (Fiber to the Home) to support high bandwidth demands.	ITU-T G.984
EPON (Ethernet PON)	Ethernet-based PON, providing 1 Gbps symmetrical speed (10G-EPON supports up to 10 Gbps). Defined by IEEE 802.3, suitable for scenarios with high Ethernet compatibility requirements.	IEEE 802.3
10G-PON (XG-PON/XGS-PON)	Next-generation PON technology supporting 10 Gbps speeds. XG-PON (asymmetric, 10G downstream / 2.5G upstream) and XGS-PON (symmetric, 10G both ways). Used for 5G, 4K video, and cloud computing high-bandwidth needs.	ITU-T G.987 / G.9807
NG-PON2	Supports multiple wavelengths (TWDM) and offers 40 Gbps or higher. Suitable for ultra-high bandwidth and flexible deployment scenarios.	ITU-T G.989

Asterfusion Campus Access Connectivity with GPON OLT SFP Modules Powered by SONiC

As campuses and small-to-medium enterprises (SMEs) move toward smarter digital environments, traditional Ethernet access networks struggle to meet the growing demands for bandwidth, flexibility, and scalability. Asterfusion’s solution combines GPON OLT SFP modules with open switches driven by the SONiC operating system to build a fully optical access architecture. This approach offers an open, flexible, and cost-effective solution that can be centrally managed via an OpenWiFi-compatible controller.

Key advantages of this solution include:

• Modular, hot-swappable OLT SFP modules enable PON functionality directly on Asterfusion SONiC switches without requiring separate OLT devices;
• Unified management of both wireless and wired devices is enabled through an OpenWiFi-compatible controller.
• Automated configuration is also supported by the OpenWiFi controller.
• High-bandwidth access realized by Passive Optical Network (PON) technology, with scalable AP deployment supported by the splitter ratio design of the SFP slots;
• Over 30% savings in deployment and operational costs compared to traditional Ethernet method.

Campus Access Connectivity with GPON OLT SFP Modules Powered by SONiC

• One CX202P-24S-M-H supports up to 48 ODNs for extremely large deployments, totaling 336 at the ODN layer. Each ODN connects 32 APs, supporting up to 10752 APs, each one supporting up to 300 Mbps bandwidth, easily meeting the demands of high density.

• OpenWiFi based Network Controller : Asterfusion provide a centralized platform for unified management of wired and wireless networks, supporting automation, monitoring, and flexible deployment options.

This future-ready network access solution is ideal for campus and SME deployments, balancing efficiency, cost, and flexibility.

CIf you’re interested in our solution, feel free to contact us! bd@cloudswit.ch