Explain Sliding Window

The TCP receive window size is the amount of received data (in bytes) that can be buffered during a connection. The sending host can send only that amount of data before it must wait for an acknowledgment and window update from the receiving host. Sliding Window is when the size of the window changes in accordance with the traffic(congestion) in the Network. Higher the Congestion, Lesser the Window size will be. Here are more finer details though not required. No one will ask you that much in detail. When a receiver advertises the window size of 0, the sender stops sending data and starts the persist timer. The persist timer is used to protect TCP from the dead lock situation. The dead lock situation could be when the new window size update from the receiver is lost and the receiver has no more data to send while the sender is waiting for the new window size update. When the persist timer expires the TCP sender sends a small packet so that the receivers Acks the packet with the new window size and TCP can recover from such situations.