Unveiling the Power of GPON in Modern FTTH Networks

Why Is GPON a Preferred Choice in FTTH Network?

GPON Network, or Gigabit Passive Optical Network, as defined by ITU-T recommendation series G.984.x, stands out in the realm of fiber-optic communication for several compelling reasons. It surpasses its predecessors like ATM PON (APON) and broadband PON (BPON) by offering increased bandwidth and versatile support for various types of traffic, including Ethernet, ATM, and TDM (PSTN, ISDN, E1, and E3).

Key Advantages of GPON in FTTH Networks

Enhanced Bandwidth

GPON represents a significant leap in bandwidth compared to earlier PON technologies. This increased capacity is pivotal for accommodating the growing demand for high-speed internet and multimedia services.

Triple-Play Services Support

GPON is designed to support triple-play services, encompassing data, voice, and IP video. This versatility makes it an ideal choice for delivering a comprehensive range of services to end-users.

Extended Reach

With a reach of up to 20 km, GPON can cover large geographical areas, making it suitable for various deployment scenarios, particularly in Fiber to the x (FTTx) networks.

FTTH Application

In the context of Fiber to the Home (FTTH) applications, GPON excels. The passive optical network (PON) architecture in FTTH is a point-to-multipoint system where unpowered optical splitters enable a single optical fiber to serve multiple premises (32-128). This makes GPON a cost-effective solution for residential and small business connectivity.

Scalability and Efficiency

GPON's ability to serve multiple users from a single fiber, combined with its scalability, makes it an efficient solution for network providers aiming to reach a large number of subscribers.

As we delve further into this article, the focus will shift towards exploring the components and architecture of GPON FTTH access networks, providing insights into the technology that underpins its popularity in modern fiber-optic communication.

Components of GPON FTTH Access Network

In a GPON FTTH access network, there are three main components: optical line terminal (OLT), optical splitters and optical network terminal (ONT).

Figure 1: Components of GPON FTTH Network

OLT (Optical Line Terminal)

The OLT functions as the endpoint for service providers in a passive optical network, typically situated in a data center or main equipment room. Serving as the powerhouse for FTTH systems, the OLT transforms optical signals into electrical signals, presenting them to a core Ethernet switch. In doing so, it replaces multiple layer 2 switches at distribution points. The OLT's distributed signal connects to backbone cabling or horizontal cabling through optical splitters, establishing links with optical network terminals at individual work area outlets.

ONT/ONU (Optical Network Terminal/Unit)

Deployed at customer premises, the ONT/ONU connects to the OLT via optical fiber, with no active elements in the link. In GPON, the transceiver within the ONT/ONU establishes the physical connection between customer premises and the central office OLT. The ONT/ONU serves as the interface for end-users, facilitating the conversion of optical signals back into electrical signals for seamless connectivity to various devices such as computers, phones, and televisions in a Fiber to the Home (FTTH) network.

Optical Splitter

The optical splitter divides the signal power, allowing a single fiber link entering the splitter to be split into multiple fibers. Multiple levels of fibers often correspond to various levels of splitters, facilitating the shared use of each fiber by numerous users. Passive optical splitters offer broad operating wavelength ranges, low insertion loss, uniformity, compact dimensions, high reliability, and support for network survivability and protection policies.

Architecture of GPON FTTH Access Networks

Employing a tree topology, GPON ensures maximum coverage with minimal network splits, effectively minimizing optical power requirements. The architecture of an FTTH (Fiber to the Home) access network can be delineated into five distinct areas: a core network area, a central office area, a feeder area, a distribution area and a user area/customer premises (see the picture below).

Figure 2: Architecture of GPON FTTH Network

Core Network

The core network integrates essential components such as ISP equipment, PSTN (public switched telephone network) - whether packet-switched or legacy circuit-switched - and cable TV provider equipment. This centralized hub forms the backbone of FTTH architecture.

Central Office

Serving as a pivotal location, the central office hosts the Optical Line Terminal (OLT) and Optical Distribution Frame (ODF), providing necessary powering. It may also house certain elements of the core network, consolidating key functionalities in one central hub.

Feeder Network

Extending from the ODF in the central office (CO) to distribution points, typically street cabinets known as Fiber Distribution Terminals (FDTs), the feeder network incorporates level-1 splitters. The feeder cable adopts a ring topology, enhancing reliability and providing Type B protection.

Distribution Network

The distribution cable links the level-1 splitter within the FDT to the level-2 splitter, often hosted in a pole-mounted box called a Fiber Access Terminal (FAT) at the neighborhood entrance. This level-2 splitter further refines signal distribution.

User Area

In the user area, drop cables establish connections from the level-2 splitter inside the FAT to subscriber premises. To facilitate maintenance, an aerial drop cable terminates at the subscriber's entrance via a Terminal Box (TB). Subsequently, an indoor drop cable links the TB to an Access Terminal Box (ATB) within the home. A patch cord then completes the connectivity, linking the Optical Network Terminal (ONT) to the ATB.

Summary

Gigabit Passive Optical Network (GPON) stands out among other passive optical networks thanks to its immense benefits. A GPON-based FTTH network architecture is reliable, scalable, and secure. Since it is a passive network, there are no active components from the CO to the end user, which dramatically minimizes the network maintenance cost and requirements. The GPON-based FTTH is a future-proof solution for providing broadband services.