This paper discusses techniques added for the sake of packet conservation in TCP. Three problems addressed are connections not getting to equilibrium, senders injecting new packets before old ones exit, and equilibrium not being attained due to limited resources on the path. The first problem is fixed through slow start. For every ack that arrives, two new ones are generated, opening the window exponentially.
The second problem is due to not estimating variation of round-trip time, ultimately causing packets to be retransmitted whose delivery has only been delayed; the authors provide an estimation method and also suggest the use of an exponential backoff timer for retransmits. The solution to this second problem, that is, taking variation into account, is one of the most important contributions of the paper because it hugely reduces the number of packets needing to be retransmitted. For the third problem, the authors note that a timeout is a good indicator of packet loss, which is a good indicator of congestion, hence suggestion to use timeout as a signal of congestion. Upon receiving a timeout, the congestion window is halved, and for each ack the congestion window is increased by 1/(congestion window).
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