Thin-streams and TCP
  ====================
  A wide range of Internet-based services that use reliable transport
  protocols display what we call thin-stream properties. This means
  that the application sends data with such a low rate that the
  retransmission mechanisms of the transport protocol are not fully
  effective. In time-dependent scenarios (like online games, control
  systems, stock trading etc.) where the user experience depends
  on the data delivery latency, packet loss can be devastating for
  the service quality. Extreme latencies are caused by TCP's
  dependency on the arrival of new data from the application to trigger
  retransmissions effectively through fast retransmit instead of
  waiting for long timeouts.
  
  After analysing a large number of time-dependent interactive
  applications, we have seen that they often produce thin streams
  and also stay with this traffic pattern throughout its entire
  lifespan. The combination of time-dependency and the fact that the
  streams provoke high latencies when using TCP is unfortunate.
  
  In order to reduce application-layer latency when packets are lost,
  a set of mechanisms has been made, which address these latency issues
  for thin streams. In short, if the kernel detects a thin stream,
  the retransmission mechanisms are modified in the following manner:
  
  1) If the stream is thin, fast retransmit on the first dupACK.
  2) If the stream is thin, do not apply exponential backoff.
  
  These enhancements are applied only if the stream is detected as
  thin. This is accomplished by defining a threshold for the number
  of packets in flight. If there are less than 4 packets in flight,
  fast retransmissions can not be triggered, and the stream is prone
  to experience high retransmission latencies.
  
  Since these mechanisms are targeted at time-dependent applications,
  they must be specifically activated by the application using the
  TCP_THIN_LINEAR_TIMEOUTS and TCP_THIN_DUPACK IOCTLS or the
  tcp_thin_linear_timeouts and tcp_thin_dupack sysctls. Both
  modifications are turned off by default.
  
  References
  ==========
  More information on the modifications, as well as a wide range of
  experimental data can be found here:
  "Improving latency for interactive, thin-stream applications over
  reliable transport"
  http://simula.no/research/nd/publications/Simula.nd.477/simula_pdf_file