What do you know about TCP window?

TCP window is the size of the buffer that the sender is willing to use for transmitting data without waiting for acknowledgment from the receiver. It is used for flow control and preventing buffer overflow at the receiver. The window size dynamically changes during the connection.

Main aspects:

• Flow control: Ensures that a fast sender does not overwhelm a slow receiver.
• Reliability: Allows multiple segments to be sent before receiving ACK, increasing throughput in high-latency networks.
• Window scaling (TCP Window Scale Option): An extension to TCP that allows the use of larger window sizes (up to 1 GB), which is critical for high-speed networks with long channels.

Example of operation:

The sender sends data segments within the current window size. Each received segment is acknowledged (ACK), informing the sender of the received data and the current available buffer size (new TCP window). The sender can only send new data until the total size of unacknowledged and unsent data does not exceed the window size announced by the receiver.

// Example of sending segments within the window
// Assume window size is 64KB
// Send 16KB
// Remaining space in window: 48KB

// Send another 32KB
// Remaining space in window: 16KB

// Send another 16KB
// Window space exhausted, waiting for ACK from receiver

// Receive ACK for the first 16KB
// Window size increased by 16KB (now 16KB + 16KB = 32KB available for new data)
// Can send another 32KB