Active Queue Management

TCP is not good for short flows. Definition: TCP friendliness – does a protocol back off when a loss occurs? TCP is not TCP friendly. Analogy: elephants vs. mice. Elephants are data intensive connections and mice are short connections. The elephants step on the mice because the data intensive connections get most of the bandwidth. The mice go through slow start each time, rarely getting to the point where they get their fair share of the bandwidth. Congestion gateway \ UW / \ / The border router should know what congestion there is between \ / the border router and Yahoo based on past connections to Yahoo. Border router Should control packets be treated differently than data packets? In the Internet today, every packet is equal. Maybe there should be a bit set for BGP packets to give them priority. This isn't happening today because of legacy issues. There is one proposal that says that slow start should start at four packets instead of one packet. This would cause the shorter connections to startup faster and acquire a fairer share of bandwidth. A loss at the beginning of a TCP connection can really reduce throughput for a shorter connection. Anecdote: At IBM, a study was done that asked people if they would prefer a variable or fixed delay when typing and getting keystrokes echoed back to them. People liked a fixed delay, so adding delay to equalize the delay of the echoed key strokes improved the user experience. Activity: get information back to the sender to get better control. Goals of active queue management: 1. Efficiency 2. Fairness