Definicija: A message transmitted to indicate that data has been received correctly. The Transmission Control Protocol (TCP) requires that the recipient acknowledge successful receipt of data. Such acknowledgments (ACKs) generate additional network traffic, decreasing the rate at which data passes but increasing reliability. To reduce the impact on performance, most hosts send an acknowledgment for every other segment or when a specified time interval has passed.

Definicija: a postal service which returns to the sender of a letter (usually registered; in the case of a parcel, it may be insured) a form or card signed by the recipient. This is evidence that the letter was received.

Definicija: poštna storitev, pri kateri naslovnik vročitev potrdi na posebnem obrazcu, ki se imenuje povratnica. Povratnica se pošiljatelju pošiljke pošlje kot navadno pismo.