TCP service is obtained by having both the sender and receiver create end points, called sockets.
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Host A sends a TCP segment (Seq = 43, ACK = 103), to which host B replies with a TCP segment (Seq = 103, ACK = 57). The payload of the first TCP segment is
A. 57 bytes long
B. 46 bytes long
C. 43 bytes long
D. 14 bytes long
Many client-server applications (e.g. DNS) that have one request and one response use UDP.
UDP transmits segments consisting of an 8-byte header followed by the payload.
UDP will be replaced by TCP, as UDP is too slow.