Slow Start and Congestion Avoidance
Before this, TCP would start to transmit as much data as was allowed in the advertised window.
A new window was added called the congestion window.
- It is not negotiated, it is assumed. It starts out with one segment
- Segment size is variable, but usually set to 512 or 536 bytes
Multiply this by the millions of hosts that are conversing on the Internet and you can see that immediate congestion follows.
Slow start initializes a congestion window of 1 segment
- Each subsequent ACK increments this window exponentially
(1, 2, 4, 8, etc.) eventually to the advertised window size
As long as there are no time-outs or duplicate ACKs during the transmission between two stations, it stays at the advertised window size.