parameter tcp_retries1

A UNIX Parameter
$cat /proc/sys/net/ipv4/tcp_retries1
3
$echo 4 > /proc/sys/net/ipv4/tcp_r

Parameter Definition
This value influences the  time, after which TCP decides,
that  something  is   wrong  due  to  unacknowledged  RTO
retransmissions,  and  reports   this  suspicion  to  the
network   layer.   RFC   1122  recommends   at   least  3
retransmissions, which is the default.

Parameter Code Internals


snippet 1
{
.procname = "tcp_retries1",
.data = &sysctl_tcp_retries1,
.maxlen = sizeof(int),
.mode = 0644,
.proc_handler = proc_dointvec_minmax,
.extra2 = &tcp_retr1_max
},

snippet 2
if (retransmits_timed_out(sk, sysctl_tcp_retries1, 0, 0)) {
/* Black hole detection */
tcp_mtu_probing(icsk, sk);

dst_negative_advice(sk);
}


Related From Research Paper
In this paper we have investigated TCP behavior in a 802.11b wireless Infrastructure network by means of experiments in a wireless network testbed. We have compared results obtained with similar experiments done in NS2 simulator. We conclude that TCP ACK skipping indeed improves TCP performance in real-life wireless LANs. Although the original goal was to explore the simultaneous-send problem reported in [1], several other insights were also obtained. The NS2 simulations showed the simultaneous-send problem manifest when MAC retries were disabled. However we were unable to reproduce the NO MAC retries case. Unlike in the NS2 simulator, various status indicators cannot be tracked in real experimentation. Instead the simultaneous-send phenomenon was observed using standalone network sniffers.
source: Experimental Evaluation of the TCP Simultaneous-Send Problem in 802.11 Wireless Local Area Networks Sumathi Gopal WINLAB, Rutgers University 73, Brett Road Piscataway, NJ 08854-8048 001 609 720 1202 sumathi@winlab.rutgers.edu Dipankar Raychaudhuri WINLAB, Rutgers University 73, Brett Road Piscataway, NJ 08854-8048 001 732 445 0877 ray@winlab.rutgers.edu
 

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