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Introduction To PON (Passive Optical Network) And Its Network Architecture

Time: 2023-06-25
        PON is short for Passive Optical Network, a mainstream fixed-line access technology that enables simultaneous access for multiple users over a single optical fiber. It has been deployed on a large scale in China since 2006, expanding from initial residential and commercial user access to large enterprise parks and industrial networks, with increasingly diverse application scenarios.
        PON features a point-to-multipoint (P2MP) structure, consisting of three core components: Optical Line Terminal (OLT), Optical Network Unit (ONU), and Optical Distribution Network (ODN). The network architecture is shown in Figure 1.
Network architecture diagram of PON
Figure 1 PON Network Architecture Diagram
    • OLT (Optical Line Terminal):
      As the carrier-side equipment at the "upper end" of the optical fiber network, the OLT communicates with user-side ONUs through the ODN. It is typically deployed in carrier base stations or service node equipment rooms.
    • ONU (Optical Network Unit):
      As user-side equipment, the ONU receives data sent by the OLT and provides direct services to end users. The OLT and ONU adopt master-slave communication, with the OLT managing signaling and monitoring information from the ONU.
    • ODN (Optical Distribution Network):
      As the passive optical transmission network between the OLT and ONU, the ODN is composed of optical fibers and optical splitters, providing physical optical transmission channels between the two devices. It supports single-stage or dual-stage optical splitting; dual-stage splitting is widely adopted in actual engineering.
        Various PON technologies have evolved with network development, including early narrowband PON, APON, BPON, mainstream EPON, GPON, 10G EPON, XG-PON, XGS-PON, and the upcoming 50G-PON. While technical differences exist between these solutions, user-perceivable variations mainly lie in line rate, available bandwidth, operating wavelength, and user capacity. The basic network architecture and working principle remain similar across all PON types.
        Notably, PON is called a "passive optical network" because the ODN contains no electronic components or power supply—it only uses passive optical devices such as optical splitters and connectors. The OLT and ONU themselves are still active powered devices.
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