The receiver has one state variable:

• windowStart (initial value 0) is the start index of the receive window.

Save it and send an acknowledgment for the packet.

Forward acknowledged packets at the beginning of the window to the application layer and advance windowStart past these packets.

Just send an acknowledgment for the packet. The sender must not have received the previous acknowledgment.

The same as the sequence number of the received packet.

Reliable Data Transfer Receiver

	Alternating Bit	Go Back n	Selective Repeat	Cumulative Acknowledgment
Receiver initialization
Response to an incoming packet with the expected sequence number
Response to an incoming packet with an unexpected sequence number
Receiver acknowledgment sequence number