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 Stick 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

What is EPON, GPON, XG-PON & XGS-PON, and How to Choose it ?

For information on what GPON is, as well as introductions to EPON, GPON, XG-PON, and XGS-PON and how to choose between them, please refer to this article: How to Choose From EPON, GPON, XG-PON & XGS-PON,Ultimate Guide to PON Technologies

Asterfusion GPON Solution Powered by SONiC and GPON OLT Stick SFP modules

Asterfusion integrates GPON OLT Stick SFP modules directly into SONiC-powered switches to create a fully optical, open, and centrally managed access network without the need for standalone OLT devices. The solution consists of five key components:

1. GPON OLT Stick SFP Modules
   • Compact, hot-swappable, SC-type modules (Class B+/C+, 1490 nm TX, 1310 nm RX)
   • Inserted into SONiC switch SFP+ ports, compatible with white-box switches
2. SONiC-Powered Network Switches (AsterNOS)
   • Preloaded with enterprise SONiC OS supporting rich L2/L3 features
   • FRRouting (BGP, OSPF), VXLAN, BGP-EVPN, LLDP, ZTP
3. Optical Distribution Network (ODN)
   • Passive PLC splitter-based network (typical 1:16 or 1:32 split ratio)
   • No power needed, easy installation, zero maintenance
4. ONU GPON Access Points
   • GPON uplink with high user capacity
   • Multiple Gigabit LAN ports, multiple SSIDs for segmentation
   • Dual-band Wi-Fi 6 or tri-band Wi-Fi 7 for high throughput
5. OpenWiFi-Compatible Controller
   • Enables unified management and automated configuration of both wireless and wired devices

Asterfusion GPON Spine-Leaf Architecture for High-Performance Campus Access

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

Campus Access Connectivity with GPON OLT SFP Modules Powered by SONiC

Why it stands out:

• Plug-and-play PON: Modular, hot-swappable OLT Stick SFP modules deliver PON capability directly on Asterfusion SONiC switches—no standalone OLT needed.
• Centralized management: Unified management and automated configuration of both wireless and wired devices via an OpenWiFi-compatible controller.
• Massive scalability: Each SONiC switch SFP port supports up to a 1:128 split ratio, connecting up to 128 APs.
• Cost efficiency: Achieve over 30% savings in deployment and operational expenses compared to traditional Ethernet approaches.

With Asterfusion, campuses and SMEs can unlock high-performance, all-optical connectivity—built for the demands of today and the opportunities of tomorrow.

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

Q&A

What’s the difference between a GPON OLT SFP and a GPON OLT Stick SFP?

In fiber network deployments—especially GPON networks—many people have trouble distinguishing between a GPON OLT SFP and a GPON OLT Stick SFP. While they share similar functions, their purpose, design, and application scenarios differ significantly. Below is a brief explanation of each device and their key differences to help clear up the confusion.

Comparison Item	GPON OLT SFP	GPON OLT Stick SFP
Is a standalone OLT device required?	Yes	NO
Can it be used with an SFP Ethernet switch?	NO	Yes
Does it include OLT forwarding logic?	NO	Yes
Main functions	Only responsible for physical layer optical signal transmission and reception	It integrates optical modules and some OLT functions (such as bandwidth management and protocol processing).
Optical chips	GPON PHYchip	GPON MAC+PHYChip with control logic
CPU	NONE	Onboard microcpu
storage	NONE	Onboard RAM and Flash
Management System	NONE	Tailored Linux management system
Hardware requirements	It needs to be inserted into an independent OLT device and relies on the processing capabilities of the OLT.	It can be inserted into general devices that support SFP (such as switches and routers), without the need for dedicated OLT equipment.
Deployment complexity	It needs to be configured in a complete OLT system and is complex to deploy.	Plug and play, easy to deploy, suitable for small and middile scale networks.
cost	Usually the cost is lower, but it requires additional OLT equipment support.	The cost may be higher, but it reduces the reliance on standalone OLT equipment.
Power consumption	The power consumption is low and depends on the overall power consumption of the OLT equipment.	The power consumption may be slightly higher due to the integration of more functions.