Why do I see a RST, ACK packet instead of a RST packet? SYN --> <-- SYN ACK ACK --> In the case of a RST ACK, The device is acknowledging whatever data was sent in the previous packet (s) in the sequence with an ACK and then notifying the sender that the connection has closed with the RST The device is simply combining the two packets into one, just like a SYN ACK
Why is the last ACK needed in TCP four way termination The question of why the last ACK is required is just that nay FIN only means that the sender of the FIN is done sending, and it must still be open to receive more segments, and it must resend any unacknowledged segments Each side is a peer (client server is an application concept), and both sides must agree that everything is done
Why need Ack flag if we already have ack number in TCP The ACK flag indicates that the Acknowledgment Number field is significant, ie containing a meaningful value When a socket connection has already been established that is nearly always the case, but it isn't while a connection is being established Acknowledgment Number: 32 bits If the ACK control bit is set this field contains the value of the next sequence number the sender of the segment
TCP Fast Retransmit and duplicated acknowledgements Ask I can't claim i know the exact reasons it is that specific number without some research, but i would think this is taking into account long distant network connections and how they behave TCP adapts itself to delays in a network and the timeout window can adjust accordingly Fast retransmit helps here to act faster than waiting for a timeout window
TCP and Go-Back-N - Network Engineering Stack Exchange 1 TCP :cumulative ack for the last correctively received, in-order seg 2 cumulative and correctly received but out-of-order segs are not individually acked ⇒ TCP sender need only maintain SendBase and NextSeqNum What is the meaning of cumulative ACK? and what is the difference between selective ACK? and why TCP uses the first one?
Window Size and ACK Number - Network Engineering Stack Exchange Copy-pasting from my lecturer's slides: • Receiver indicates the window size is 3000 • Transfer goes ahead • Acknowledge every 3000 bytes • Receiver increases window size to 4000 • 4000 bytes
NACK vs. ACK? When to use one over the other one? 23 Personally I don't even feel that there is a need for ACK It's faster if we just send NACK (n) for the lost packets instead of sending an ACK for each received packet So when which situations would one use ACK over NACK and viceversa?
Why the TCP client havent receive the ACK response, it send the FIN . . . If the receiver doesn't receive data, it will send a duplicate ACK to the sender So the sender waits for a time and if it doesn't receive acknowledgment of the FIN or data within this time, or if it receives a duplicate ACK, it will retransmit the packets ACK control flag is always sent once a connection is established; As RFC 793 says:
Why do we need a 3-way handshake? Why not just 2-way? Because a SYN-ACK is an ACK, the client now knows for sure that it can send packets to the server And because a SYN-ACK is a SYN, it also knows that the server wants proof that this message got through So it sends back an ACK: just a plain ACK this time, because it doesn't need proof anymore that its packets can get through