The Linksys SPA-400 is a 4-port analog telephone adapter that allows users to connect up to four analog phones or fax machines to a voice-over-IP (VoIP) network. It features support for a variety of VoIP protocols, including SIP and SPCP, and includes advanced call features such as caller ID, call waiting, and voicemail. The SPA-400 also includes built-in security features such as password protection and encryption to ensure the privacy and security of data transmitted over the network.

The SPA-400 is a router manufactured by the company Linksys that allows multiple devices to connect to a network and communicate with each other. It works by receiving data packets from devices and forwarding them to their intended destination. The router is assigned a unique IP address , which serves as its identifier on the network.

To access the router's settings and configure its functions, users can log in using a web browser and their and . Once logged in, users can customize various settings such as network name, password, and security protocols. They can also set up parental controls, prioritize bandwidth usage, and monitor network activity.