Complex sentence: A keepalive signal is often sent at predefined intervals, and plays an important role on the Internet: if no reply is received, the link is assumed to be down and future data will be routed via another path until the link is up again.
Split into simpler sentences: A keepalive signal is often sent at predefined intervals, and plays an important role on the Internet. After a signal is sent, if no reply is received the link is assumed to be down and future data will be routed via another path until the link is up again.