RFC 2581 (rfc2581) - Page 2 of 14
TCP Congestion Control
Alternative Format: Original Text Document
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