Piggybacking

Question

When piggybacking occurs then sender is not send any data until receiver will not send acknowledgement.when will receiver send the ack .?

Comments

Piggybacking has nothing to do with what you mentioned. Instead, When ACK is Piggybacked, that means sender / rcvr is sending ACK along with (inside) the data packet.

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When ack is piggybacked then next packet packet is send by receiver or sender?please explain it.

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Whether ACK is piggybacked or not, who should send the next packet, depends on the flow control mechanism - Stop & Wait, Sliding Window. TCP using Sliding Window. So, here sender / rcvr will send a window of packets rather than a packet at a time. Sender / Rcvr does not wait for to send next packet. They send the packets as per window size (negotiated during connection establishment / changed as per network congestion) and then ACK s rcvd (usually cumulative).

So, when ACK is piggybacked (or is not), anyone can send packets. Receiver might piggyback an ACK and then send the next packet of window / Receiver might piggyback an ACK and then sender might send next packet.

If a sender is waiting for ACK from receiver (because sender has already sent packets equal to window size and has received no ACK from receiver), then on receiving ACK (piggybacked or plain ACK), the sender would send the next packet

Answer 1

Piggybacking is the process in flow control protocols in which to improve Efficiency, the receiver after receiving the packer, holds the acknowledgement until it has something to send to the sender, when receiver gets some data to send to the receiver, it combines the acknowledgement with the data and it send it in one packet to the sender. So the answer to your question is "The Receiver will send the ack after it gets something to send to the sender from Upper layers".