10.1.4 The amount of data that needs to be transmitted is often too large to be sent in a single data segment. In this case, the data must be broken into smaller pieces to allow for proper data transmission. TCP is responsible for breaking data into segments. This can be compared to the way that small children are fed. Their food is cut into smaller pieces that their mouths can accommodate. Additionally, a device may not be able to receive data as quickly as the source can send it. The device may be busy with other tasks or the sender may be a more robust device.
Once the data is segmented, it must be transmitted to the destination device. One of the services provided by TCP is flow control, which regulates how much data is sent during a given transmission period. The process of flow control is known as windowing.
Window size determines the amount of data that can be transmitted at one time before the destination responds with an acknowledgment. After a host transmits the window-sized number of bytes, the host must receive an acknowledgment that the data has been received before it can send any more data. For example, if the window size is 1, each byte must be acknowledged before the next byte is sent.
TCP utilizes windowing to dynamically determine transmission size. Devices negotiate a window size to allow a specific number of bytes to be transmitted before an acknowledgment.
This process of dynamically varying the window size increases reliability. The window size can be varied based upon acknowledgments.
The Interactive Media Activity will help students understand the concept of windowing.
The next page describes TCP sequence numbers.
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