tcp tuning tcp_abc

echo 1 > /proc/sys/net/ipv4/tcp_abc
From RFC 34100.

A Modified Algorithm for Increasing the Congestion Window

   As originally outlined in [Jac88] and specified in [RFC2581], TCP
   uses two algorithms for increasing the congestion window.  During
   steady-state, TCP uses the Congestion Avoidance algorithm to linearly
   increase the value of cwnd.  At the beginning of a transfer, after a
   retransmission timeout or after a long idle period (in some
   implementations), TCP uses the Slow Start algorithm to increase cwnd
   exponentially.  According to RFC 2581, slow start bases the cwnd
   increase on the number of incoming acknowledgments.  During
   congestion avoidance RFC 2581 allows more latitude in increasing
   cwnd, but traditionally implementations have based the increase on
   the number of arriving ACKs.  In the following two subsections, we
   detail modifications to these algorithms to increase cwnd based on
   the number of bytes being acknowledged by each arriving ACK, rather
   than by the number of ACKs that arrive.  We call these changes
   "Appropriate Byte Counting" (ABC) [All99].


Read more: http://www.faqs.org/rfcs/rfc34100.html#ixzz0mJkZPK7k