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Wiktionary:
(electronics, communication) a short message sent by one device to another to check that the link between the two is operating, or to prevent this link from being broken due to inactivity

ülevaateid
https://www.techopedia.com/definition/28979/keepalive

https://en.wikipedia.org/wiki/Keepalive

http://tldp.org/HOWTO/TCP-Keepalive-HOWTO/overview.html

https://www.cisco.com/c/en/us/support/docs/content-networking/keepalives/118390-technote-keepalive-00.pdf

https://tldp.org/HOWTO/pdf/TCP-Keepalive-HOWTO.pdf