Fiber to the Home Explained: A Deep Dive into PON and AON Networks

Fiber to the Home (FTTH) is a broadband network technology that uses optical fiber to deliver communications signals directly to homes. Compared to traditional copper cable access, FTTH offers higher bandwidth, faster transmission speeds, and longer transmission distances.?With the rapid development of internet applications and increasing demand for high-speed broadband, FTTH has become the mainstream choice for broadband access.

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There are two main implementations of FTTH networks: Passive Optical Network (PON) and Active Optical Network (AON). PON relies on passive splitters to distribute optical signals, while AON uses active equipment (such as switches and routers) for signal amplification and distribution.

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?1. Optical Communication Technology

To understand FTTH networks, we first need to understand the basic principles and related technologies of optical communication. Optical communication uses the propagation characteristics of optical signals in optical fibers for data transmission. An optical fiber is a thin, flexible fiber made of glass or plastic, with extremely low signal loss and very high transmission rates, making it the core medium of modern communication systems.

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2. Types of Optical Fibers

Optical fibers are mainly divided into?single-mode fibers (SMF) and multi-mode fibers (MMF).

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Single-mode Fiber (SMF):?Has a small core diameter (typically 8-10 microns), allowing only one mode of light transmission. SMF has low signal loss, suitable for long-distance and high-bandwidth transmission.

Multi-mode Fiber (MMF):?Has a larger core diameter (typically 50 or 62.5 microns), allowing multiple modes of light transmission. MMF has higher signal loss and is usually used for short-distance transmission.

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3. FTTH Network Implementations:?PON and AON

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3.1. Passive Optical Network (PON)

A PON is an optical fiber network that requires no intermediate active equipment (such as amplifiers or switches).?In a PON system,?an Optical Line Terminal (OLT) located at the service provider's end connects to multiple Optical Network Units (ONUs) or Optical Network Terminals (ONTs) at the user's end through a passive splitter. PON systems are cost-effective and easy to maintain, making them widely used in FTTH networks.

Technologies and Standards:

??GPON (Gigabit-capable PON): An ITU-T standard, with downstream speeds up to 2.5Gbps and upstream speeds up to 1.25Gbps.

??EPON (Ethernet PON): An IEEE standard, with symmetrical speeds of 1Gbps, and supports the 10G-EPON standard for higher speeds.

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Key Components:

??OLT (Optical Line Terminal):?The core device located at the central office, responsible for signal processing, bandwidth allocation, and network management.

??ONU/ONT (Optical Network Unit/Terminal):?Located at the user end, converts optical signals to electrical signals and vice versa.

??Splitter:?A passive component that divides the optical signal from the OLT to multiple ONUs/ONTs.

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3.2. Active Optical Network (AON)

An AON relies on active equipment such as switches and routers for signal amplification and distribution, providing point-to-point connections between the central office and each user.

Technologies and Standards:

??Ethernet AON:?Based on IEEE 802.3 Ethernet standards, using Ethernet switches for data forwarding and management.

??WDM AON (Wavelength Division Multiplexing AON):?Uses different wavelengths to transmit multiple data channels on the same fiber, each user having a dedicated wavelength.

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Key Components:

??OLT (Optical Line Terminal):?Similar to PON, located at the central office.

??ONU/ONT (Optical Network Unit/Terminal):?Similar to PON, located at the user end.

??Switches and Routers:?Core components that forward, amplify, and manage optical signals.

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4. Comparison Between PON and AON

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Network Architecture:

PON:?Point-to-multipoint, using passive splitters, centralized management.

AON:?Point-to-point, using active equipment, distributed management.

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Bandwidth:

PON:?Shared bandwidth among users, with potential contention during peak times.

AON:?Dedicated bandwidth for each user, offering higher and more stable transmission rates.

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Latency:

PON:?Lower latency due to passive components, but potential delays from shared bandwidth.

AON: Some processing delay from active equipment, but overall lower and more stable latency.

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Transmission Distance:

PON:?Generally limited to around 20 km, with splitters' insertion loss affecting distance.

AON:?Longer distances achievable with active signal amplification and relaying.

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Cost and Maintenance:

PON:?Lower cost and maintenance due to passive components.

AON:?Higher cost and maintenance due to active components needing power and regular upkeep.

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5. FTTH Network Design and Deployment for PON

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Design Considerations:

Path Selection:?Choose the shortest, easiest routes considering existing infrastructure and obstacles.

Node Layout:?Place nodes such as OLTs, splitters, and ONUs optimally based on user distribution.

Splitter Placement:?Position splitters close to users to minimize fiber length and loss.

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Topology Structures:

Star:?Each user has an independent fiber to the central node, offering dedicated bandwidth but higher fiber usage.

Tree:?Splitters distribute signals to multiple users, optimizing fiber usage but sharing bandwidth.

Ring: Provides redundancy and fault tolerance but is more complex and costly.

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Equipment Selection:

OLT:?Based on network scale, user count, and supported standards.

ONU/ONT:?Based on user needs, interface types, and bandwidth capabilities.

Splitter:?Consider split ratio, insertion loss, and reliability.

Fiber Cable:?Choose appropriate types for different environments (single-mode, multi-mode, indoor, outdoor).

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Capacity Planning:

Bandwidth:?Plan based on user demand and usage patterns to ensure adequate capacity.

User Count:?Plan to support expected user numbers, ensuring sufficient splitter and OLT port capacity.

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Deployment:

Fiber Installation:?Lay fiber cables, connect, and protect them.

Equipment Installation and Testing:?Install and configure OLTs, ONUs, splitters, and test network performance and reliability.

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By considering these factors, FTTH networks can be designed and deployed to provide high-speed, reliable broadband access, meeting the growing demands for faster and more efficient communication services.