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IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF * SUCH DAMAGE. * * @(#)tcp_timer.h 8.1 (Berkeley) 6/10/93 * $FreeBSD: src/sys/netinet/tcp_timer.h,v 1.18 1999/12/29 04:41:03 peter Exp $ */ #ifndef _NETINET_TCP_TIMER_H_ #define _NETINET_TCP_TIMER_H_ #include /* Keep the external definition the same for binary compatibility */ #define TCPT_NTIMERS_EXT 4 /* * Definitions of the TCP timers. * * The TCPT_PTO timer is used for probing for a tail loss in a send window. * If this probe gets acknowledged using SACK, it will allow the connection * to enter fast-recovery instead of hitting a retransmit timeout. A probe * timeout will send the last unacknowledged segment to generate more acks * with SACK information which can be used for fast-retransmiting the lost * packets. This will fire in the order of 10ms. * * The TCPT_REXMT timer is used to force retransmissions. * The TCP has the TCPT_REXMT timer set whenever segments * have been sent for which ACKs are expected but not yet * received. If an ACK is received which advances tp->snd_una, * then the retransmit timer is cleared (if there are no more * outstanding segments) or reset to the base value (if there * are more ACKs expected). Whenever the retransmit timer goes off, * we retransmit one unacknowledged segment, and do a backoff * on the retransmit timer. * * The TCPT_DELACK timer is used for transmitting delayed acknowledgements * if an acknowledgement was delayed in anticipation of a new segment. * * The TCPT_PERSIST timer is used to keep window size information * flowing even if the window goes shut. If all previous transmissions * have been acknowledged(so that there are no retransmissions in progress), * and the window is too small to bother sending anything, then we start * the TCPT_PERSIST timer. When it expires, if the window is nonzero, * we go to transmit state. Otherwise, at intervals send a single byte * into the peer's window to force him to update our window information. * We do this at most as often as TCPT_PERSMIN time intervals, * but no more frequently than the current estimate of round-trip * packet time. The TCPT_PERSIST timer is cleared whenever we receive * a window update from the peer. * * The TCPT_KEEP timer is used to keep connections alive. If an * connection is idle (no segments received) for TCPTV_KEEP_INIT amount * of time, but not yet established, then we drop the connection. * Once the connection is established, if the connection is idle for * TCPTV_KEEP_IDLE time (and keepalives have been enabled on the socket), * we begin to probe the connection. We force the peer to send us a * segment by sending: * * This segment is (deliberately) outside the window, and should elicit * an ack segment in response from the peer. If, despite the TCPT_KEEP * initiated segments we cannot elicit a response from a peer in * TCPT_MAXIDLE amount of time probing, then we drop the connection. * * The TCPT_2MSL timer is used for keeping the conenction in Time-wait state * before fully closing it so that the connection 4-tuple can be reused. */ #define TCPT_REXMT 0 /* retransmit */ #define TCPT_PERSIST 1 /* retransmit persistence */ #define TCPT_KEEP 2 /* keep alive */ #define TCPT_2MSL 3 /* 2*msl quiet time timer */ #define TCPT_DELACK 4 /* delayed ack timer */ #if MPTCP #define TCPT_JACK_RXMT 5 /* retransmit timer for join ack */ #define TCPT_MAX 5 #else /* MPTCP */ #define TCPT_MAX 4 #endif /* !MPTCP */ #define TCPT_NONE (TCPT_MAX + 1) #define TCPT_NTIMERS (TCPT_MAX + 1) #endif /* !_NETINET_TCP_TIMER_H_ */