RFC 2581 (rfc2581) - Page 2 of 14

TCP Congestion Control

RFC 2581                 TCP Congestion Control               April 1999


   This document is organized as follows.  Section 2 provides various
   definitions which will be used throughout the document.  Section 3
   provides a specification of the congestion control algorithms.
   Section 4 outlines concerns related to the congestion control
   algorithms and finally, section 5 outlines security considerations.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [Bra97].

2. Definitions

   This section provides the definition of several terms that will be
   used throughout the remainder of this document.

   SEGMENT:
      A segment is ANY TCP/IP data or acknowledgment packet (or both).

   SENDER MAXIMUM SEGMENT SIZE (SMSS):  The SMSS is the size of the
      largest segment that the sender can transmit.  This value can be
      based on the maximum transmission unit of the network, the path
      MTU discovery [MD90] algorithm, RMSS (see next item), or other
      factors.  The size does not include the TCP/IP headers and
      options.

   RECEIVER MAXIMUM SEGMENT SIZE (RMSS):  The RMSS is the size of the
      largest segment the receiver is willing to accept.  This is the
      value specified in the MSS option sent by the receiver during
      connection startup.  Or, if the MSS option is not used, 536 bytes
      [Bra89].  The size does not include the TCP/IP headers and
      options.

   FULL-SIZED SEGMENT: A segment that contains the maximum number of
      data bytes permitted (i.e., a segment containing SMSS bytes of
      data).

   RECEIVER WINDOW (rwnd) The most recently advertised receiver window.

   CONGESTION WINDOW (cwnd):  A TCP state variable that limits the
      amount of data a TCP can send.  At any given time, a TCP MUST NOT
      send data with a sequence number higher than the sum of the
      highest acknowledged sequence number and the minimum of cwnd and
      rwnd.

   INITIAL WINDOW (IW):  The initial window is the size of the sender's
      congestion window after the three-way handshake is completed.





Allman, et. al.             Standards Track