When a connection is established, TCP treads lightly at first to assess the bandwidth of the connection and to avoid overflowing the receiving host or any other devices or links in the path. The send window is set to two TCP segments, and if that is acknowledged, then it is incremented to three segments. If those are acknowledged, then it is incremented again, and so on until the amount of data being sent per burst reaches the size of the receive window on the remote host. At that point, the slow start algorithm is no longer in use and flow control is governed by the receive window. However, at any time during transmission, congestion could still occur on a connection. If this happens (evidenced by the need to retransmit), a congestion avoidance algorithm is used to reduce the send window size temporarily, and to grow it back toward the receive window size. Slow start and congestion avoidance are discussed further in RFC 1122.

Note:
The slow start algorithm and congestion avoidance are supported without configuration.

See Also