The Reno TCP agent is very similar to the Tahoe TCP agent,
except it also includes fast recovery, where the current
congestion window is ``inflated'' by the number of duplicate ACKs
the TCP sender has received before receiving a new ACK.
A ``new ACK'' refers to any ACK with a value higher than the higest
seen so far.
In addition, the Reno TCP agent does not return to slow-start during
a fast retransmit.
Rather, it reduces sets the congestion window to half the current
window and resets ssthresh_ to match this value.