When the receiver has a full buffer, the window size is reduced to zero. In this state, the window is said to be 'Frozen' and the sender cannot send any more bytes until it receives a datagram from the receiver with a window size greater than zero.
A TCP/IP packet has the window size stuck for longer than the threshold interval.
If the window size is less than the maximum, the flow of data is restricted.
The sender will not exceed the receivers window size.
The receiver is overloaded.
The receiver has run out of buffer space.
There may be a problem with the receiver's TCP/IP stack.
There may too many connections to the receiver resulting in reduced buffer space.