What's the meaning of 'An acknowledgment by TCP does not guarantee that the data has been delivered to the end user, but only that the receiving TCP has taken the responsibility to do so.'

[rookie R]

i!

I don't know what this passage means, can someone please explain it for me, Thanks! Do this means I finished all my work about TCP and I receive an ACK, this just means my work is done, It's somebody else's problem. ACK is just mean my work is done, not mean the data has transport to the user because the ACK is sent by the next router who receive the data.

It's in RFC 793, 2.6. Reliable Communication

An acknowledgment by TCP does not guarantee that the data has been delivered to the end user, but only that the receiving TCP has taken the responsibility to do so.

[aspetukhov · Accepted solution]

IMHO, it's all about hierarchical model. The "user" is the "application process". TCP is just one of the layers (transport, 4th). TCP is responsible for receiving/transmitted data only.

RFC 793
1.4. Interfaces
The TCP interfaces on one side to user or application processes and on the other side to a lower level protocol such as Internet Protocol.

Let's imagine that TCP receives data. Then the data should travel to the end user (Application, 7th layer). But application may be overloaded and discards the data. In this situation the remote side received TCP-ACK, but on our side the user has not received the message.

[rookie R]

Thanks! That really helps me a lot!