public switched network (PSN)

Any switching system that provides a circuit switched to many customers. In the USA, there are four: Telex, TWX, telephone, and Broadband Exchange.; 提供線路交換給許多客戶的交換系統。在美國有Telex(電傳用戶電報)、TWX(電傳打字)、電話 和寬頻帶交換系統等四類。