A simple and feasible implementation method of fiber optic protection in EP0N System (1)

Introduction

Ethernet Passive Optical Network (EPON) is an Ethernet-based, point-to-point optical fiber access technology. It combines the simplicity of the Ethernet technology and the efficiency of the PON network, it is the best way to achieve fiber-to-user access networks in the future.

Currently, all Protection Switching methods used in the EPON system require redundant PON modules, which are costly and complicated to implement. However, as one of the access network technologies, EPON is mainly used for broadband access services of FTTH/FTTB. The user access costs are sensitive and the protection requirements are relatively low, therefore, the existing protection methods of the EPON system have less practical application value.

1. Significance of implementing Backbone Optical Fiber Protection Switching in the EPON system

EPON uses a tree-like topology with a point-to-point structure. If the backbone optical fiber fails, all the onus to which it belongs cannot communicate with the EPON network. Therefore, the survivability of backbone optical fibers ensures the reliability of the entire EPON network. At the same time, because the access optical fiber at the end of the access network cannot have multiple routes, the replacement method of the optical fiber full protection has no practical significance. Therefore, the backbone optical fiber protection switching method will be the main protection switching method to improve the reliability of the EPON system in network applications.

2. Existing optical fiber protection solutions in the EPON system

EPON international standard IEEE 802.3ah) does not define the protection method. In the "access network technical requirements-Ethernet-based Passive Optical Network EPON" formulated by the China Communications Standards Commission, it has been made clear that the use of ITU-T G.984.1 two GPON system protection methods: backbone fiber Protection Switching Mode and optical fiber full protection switching mode, 1 ~ 2:

Switch Mode of EPON system Backbone Optical Fiber Protection

All-protected Optical Fiber switching mode of EPON system

In the backbone optical fiber protection mode, the ports of the active and standby PON modules on the OLT side are connected to the two ports in the 2: N shard through the active and standby optical fiber trunk, from the Shard to The ONU side, conventional connections are used. When the active PON module of the OLT is in the active state, the Standby PON module is in the cold backup state. If the Active Optical Fiber fails or the active PON module fails, enable the standby PON module and optical fiber. When switched to the backup PON module, it takes a long time for the signal transmitting module in the backup PON module to be activated to work normally. In this way, the OLT side requires two PON modules, the master and the slave, and the backbone optical fiber cables need to be laid on the master and the slave, so as to implement protection for the backbone optical fiber segments and improve the system reliability.

In the optical fiber full protection switching mode, each ONU implements dual-homing connection with two independent optical splitter modules through the master and slave PON modules, and each splitter connects two PON ports of the AOLT. The OLT backup module adopts the hot backup mode and switches to each ONU. The Protocol needs to be switched. In this way, both the active and standby PON modules must be configured for the OLT and The ONU. The backbone optical fiber cables must be laid for the active and standby optical fibers, and two slave nodes must be set for the backbone optical fibers, the primary and secondary access optical fiber cables are laid for each ONU to protect each network element in the EPON system and improve the system reliability.

The backbone optical fiber protection method is less costly than the optical fiber full protection switching method. It only protects the backbone fiber segments of the EPON system; the optical fiber full-Protection Switching Method completely eliminates the single point of failure (spof) risks in the EPON system, but the cost also doubles as a whole.

3. Implementation of Optical Fiber Protection Switching for simple backbone in the EPON system

3.1 Implementation of simple Backbone Optical Fiber Protection Switching in EPON system

In order to achieve simple switching of backbone optical fiber protection, the EPON system should be composed of optical line terminal OLT, working optical fiber, protected optical fiber, 2: N Optical splitter, and optical network unit ONU, the OLT includes the protection switching control module, which sends a switching signal to control the Protection Switching of the system when the optical fiber fails) the PON module receives the optical signal provided by the optical access network and sends the optical signal to the user side. Meanwhile, the PON module can send an alarm based on the working conditions of the optical fiber connected to it, such as optical signal loss and signal deterioration alarms) and 1X2 optical switches. 3.

EPON system structure supporting backbone fiber protection

The PON module output PON port is connected to the 1 × 2 optical switch input. The two output ports of the optical switch are connected to the working optical fiber and the protected Optical Fiber respectively. The working optical fiber and the protected optical fiber are connected to the following Optical Fiber respectively: two input ports of the N-Shard, from 2: N-Shard to The ONU side using conventional connections, ONU using conventional ONU.

When the system works normally, the switching control module can monitor the operating status and related alarm information of the olt pon module online, when the Protection Switching Control Module receives the line fault, signal deterioration, and other warning information from the OLT, it determines whether to perform Switching Based on the preset mechanism and triggers the optical switch to implement switching, in this way, the master and slave Switches of the backbone optical fiber of the EPON system are implemented.

After the optical switch is switched, the length of the primary and secondary optical fibers cannot be the same. To avoid uplink service conflicts, the control module also triggers the PON module to re-initiate the discovery, ranging, registration, and other processes, in this way, the protection of EPON system services is reversed.

3.2 process for implementing simple optical fiber Protection Switching in the EPON system

Optical fiber Protection Switching can be performed in the following two situations: ① automatic switching: triggered by fault detection, such as signal loss; ② forced switching: triggered by a management event.