Question: In TCP, the _______ timer is needed to handle the zero window-size advertisement.

Answer:

• In TCP, the retransmission timer is needed to handle the zero window-size advertisement.
• When a TCP receiver advertises a zero window size, it means that it has no buffer space available to receive more data at the moment. This can happen if the application at the receiver end is not processing data quickly enough or if the network is congested. When the sender receives a zero window size advertisement, it must stop sending data until the receiver advertises a non-zero window size.
• To handle the situation where the receiver's window size remains zero for an extended period, TCP uses the retransmission timer. The retransmission timer is a timer that is started when a segment is sent, and it is reset each time an acknowledgment is received. If an acknowledgment is not received within the timer's expiration time, then the segment is assumed to be lost, and TCP retransmits it.
• When the sender receives a zero window size advertisement, it starts the retransmission timer for the unacknowledged segments. If the timer expires before the receiver advertises a non-zero window size, then the sender retransmits the segments. This process continues until either the receiver advertises a non-zero window size or the maximum number of retransmission attempts is reached.
• Therefore, the retransmission timer is needed to handle the situation where a receiver's window size remains zero, ensuring that data is not lost and the connection remains reliable.