Sending Behaviour

A sender has a Congestion Window (cwnd). The cwnd is defined as the bytes starting from the first unACKed byte, to the last availale byte (a set of these may already be in-flight but unACKed).

The sender will send all the bytes within its' cwnd, wait RTT for ACKs, update the cwnd, and start again.

$\displaystyle rate \approx \frac{cwnd}{RTT}bytes / second$

(3)

$\displaystyle \textrm{last byte sent} - \textrm{last byte acked} \leq cwnd$

(4)

The cwnd is adjusted based on the observed congestion, thus limiting the rate at which the sender sends packets.