sb

When an application sends or receives data from TCP, it is gets the data from the TCP buffers. Data is put into these buffers from the physical network, and the speed varies depending on packet collision and so on.

When sending, an application puts data into the buffer and continues its own processing. TCP empties the buffer as quickly as it can. If the application sends more quickly than TCP can actually send, the send buffer starts to fill up. When it is full, the send operation blocks and waits until room is available in the buffer. The converse is true for receiving.

The default buffer size provided by TCP is adequate for most applications. Applications that transfer large amounts of data can benefit by increasing the amount of data that can be buffered, for example, to 16 or 32 kilobytes. This is difficult to determine, so the sb (send buffer) and rb (receive buffer) settings allow you to experiment.