Data is collected in system buffers and must be removed using the Receive method, Search method, or Fill method. The Receive event fires to indicate that data is available. The value increases as data arrives and is collected in system buffers. The value decreases as your application calls the Receive method, Search method, or Fill method to remove data. If these methods are not invoked or are seldom invoked, then "back pressure" will be exerted at the remote host and packet transmission rates will decrease.