Many firewall or NAT systems will close a connection if there has been no activity in some time period.
The Keep Alive signal can be used to trick intermediate hosts to not close the connection due to inactivity.
A keepalive signal is often sent at predefined intervals, and plays an important role on the Internet.
Since the only purpose is to find links that do not work or to indicate connections that should be preserved, keepalive messages tend to be short and not take much bandwidth.
Transmission Control Protocol (TCP) keepalives are an optional feature, and if included must default to off.
If a certain number of keepalives are sent and no response (ACK) is received, the sending host will terminate the connection from its end.