1

When point A sends data to point B, it's delivered reliably over TCP. If the underlying channel loses data, the TCP stack on point B side automatically asks to re-transmit lost frames.

Let's assume between point A and B there are 2 different hops: x1, x2. Does each one of these hops do the same re-transmission internally? E.g. if A sends data to B using A -> x1 -> x2 -> B route and x1 -> x2 is lossy link, does x2 ask x1 to resend missing frames, or is it the final destination only (B) that asks for data to be resent and only origin (A) re-sends it?

3

Only the two endpoints, the TCP peers, even know that TCP is used. Routers route packets at layer-3, but TCP send segments at layer-4. The TCP segments are encapsulated inside the IP packets, and the routers only look at the IP headers to determine where to send the packets. They do not look at the packet payload.

So, no, the routers will not ask to resend TCP. IP is connectionless, so one router is not even expecting more packets from the other router, but it deals with them individually, regardless of what has come before, if it does receive packets from the other router.

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