Optical communication system, master station, and optical communication method

A master station device configured to perform communication with each of a plurality of slave station devices in an optical communication system, wherein:

• the plurality of slave station devices are connected in parallel to a looped path,
• a communication path between the master station device and each of the slave station devices includes:
• a normal path extending in a first direction through the looped path from the master station device to the slave station device;
• and
• a backup path extending in a second direction opposite to the first direction through the looped path from the master station device to the slave station device,
• the master station device performs communication control processing that controls communication with each of the slave station devices based on round-trip propagation time (hereinafter referred to as round trip time (RTT)) between the master station device and the slave station device,
• normal path RTT is the RTT in a case of the communication through the normal path,
• backup path RTT is the RTT in a case of the communication through the backup path,
• a first slave station device is a slave station device with which the communication through the normal path has become impossible among the plurality of slave station devices,
• first normal path RTT is the normal path RTT between the master station device and the first slave station device,
• first backup path RTT is the backup path RTT between the master station device and the first slave station device,
• first partial RTT is the RTT between the master station device and the looped path,
• loop propagation time is propagation time necessary for one trip through the looped path,
• the master station device holds the normal path RTT, the first partial RTT, and the loop propagation time of each of the slave station devices, the master station device calculates the first backup path RTT based on the first normal path RTT, the first partial RTT, and the loop propagation time,
• the master station device performs the communication control processing for each of the slave station devices based on the normal path RTT when the first slave station device does not exist, and
• the master station device resumes the communication control processing for the first slave station device based on the calculated first backup path RTT without measuring the first backup path RTT when the first slave station device is sensed.

An optical communication method of performing communication between a master station device and each of a plurality of slave station devices in an optical communication system, wherein:

• the plurality of slave station devices are connected in parallel to a looped path,
• a communication path between the master station device and each of the slave station devices includes:
• a normal path extending in a first direction through the looped path from the master station device to the slave station device;
• and
• a backup path extending in a second direction opposite to the first direction through the looped path from the master station device to the slave station device,
• communication control processing that controls communication between the master station device and each of the slave station devices is performed based on round-trip propagation time (hereinafter referred to as round trip time (RTT)) between the master station device and the slave station device,
• normal path RTT is the RTT in a case of the communication through the normal path,
• backup path RTT is the RTT in a case of the communication through the backup path,
• a first slave station device is a slave station device with which the communication through the normal path has become impossible among the plurality of slave station devices,
• first normal path RTT is the normal path RTT between the master station device and the first slave station device,
• first backup path RTT is the backup path RTT between the master station device and the first slave station device,
• first partial RTT is the RTT between the master station device and the looped path,
• loop propagation time is propagation time necessary for one trip through the looped path, and
• the optical communication method includes:
• holding the normal path RTT, the first partial RTT, and the loop propagation time of each of the slave station devices;
• calculating the first backup path RTT based on the first normal path RTT, the first partial RTT, and the loop propagation time;
• performing the communication control processing for each of the slave station devices based on the normal path RTT when the first slave station device does not exist;
• and
• resuming the communication control processing for the first slave station device based on the calculated first backup path RTT without measuring the first backup path RTT when the first slave station device is sensed.