Third and fourth phase update of control network in J-PARC MR

The control network in J-PARC is a dedicated network that enables to control distributed power supplies and measuring instruments used for the accelerator. It is independent from the office network, but some communications are permitted through a firewall. The control network consists of a lot of switches: (a) core switches in the central control building, (b) aggregation switches in each accelerator facility, and (c) edge switches. The control network started in 2005, and this year, 2025, marks its 20th anniversary. At J-PARC, the network equipment has been updated about every 7 years. The third phase of update began around 2018, and in Main Ring it was completed in 2023. This report describes how the control network changed from the original design up to the third phase of update. It also discusses the planned fourth phase, including big changes on operation and maintenance support.