Function

1. Send Ethernet data to the ONU(optical network unit) in broadcast mode;

2. Initiate and control the ranging process, and record the ranging information;

3. Allocate bandwidth for the ONU. That is, it controls the start time and the size of the sending window when the ONU sends data.

EPON is a local end device (OLT) in a passive optical network system. It is a multi-service platform that supports both IP services and traditional TDM services. It is deployed on the edge of a MAN or at the egress of a community access network, converges access services, and transmits them to the IP network.

Core components:  including aggregation distribution, service processing, and ODN adaptation functions

Service: Provides service interface functions, including interface adaptation and interface protection, as well as signaling processing and media transmission system conversion functions for specific services when required

Common parts: including power supply and OAM functions

In the EPON system, the passive optical line terminal (OLT) is the device at the core network side. Firstly, the function of OLT in EPON system is introduced briefly, and a single board OLT based on ARM9 processor is presented. 

OLT system design idea

The whole OLT system design adopts the embedded design idea. The embedded hardware platform is small in size, high in reliability, low in power consumption, rich in resources, and easy to operate, which provides convenience for debugging and upgrading software and hardware of OLT.

The hardware design of an OLT system consists of the backplane, main control board, and OLT board.

The backplane is used to connect multiple OLT boards to the main control board. In actual projects, you can design four boards (including four PON ports) or 20 boards (including 20 PON ports).

The main control board is used to control and manage multiple OLT boards, centralized management of ONUs, remote monitoring, remote commissioning and maintenance, and remote online upgrade. The MPU is connected to the OLT through the Media Independent Interface (MII). The design mainly describes the hardware design and implementation of a single OLT board.