From: Guus Sliepen <guus@sliepen.org>
Date: Mon, 14 Oct 2019 20:32:35 +0000 (+0200)
Subject: Fix retransmission timeout calculation.
X-Git-Url: http://git.meshlink.io/?a=commitdiff_plain;ds=sidebyside;h=eb85ec4ae5f32102430e0622e3855aaba110c032;hp=25675cca79330f968b3fb106793a5265615f4df7;p=utcp

Fix retransmission timeout calculation.

The RTO calculation was missing a factor 4 multiplication of the
RTT variance, which caused it to set the RTO to a much lower value than
specified by RFC 6298. This would result in more retranmissions and a
lower throughput.
---

diff --git a/utcp.c b/utcp.c
index f35f965..802d95a 100644
--- a/utcp.c
+++ b/utcp.c
@@ -415,13 +415,13 @@ static void update_rtt(struct utcp_connection *c, uint32_t rtt) {
 	if(!utcp->srtt) {
 		utcp->srtt = rtt;
 		utcp->rttvar = rtt / 2;
-		utcp->rto = rtt + max(2 * rtt, CLOCK_GRANULARITY);
 	} else {
 		utcp->rttvar = (utcp->rttvar * 3 + absdiff(utcp->srtt, rtt)) / 4;
 		utcp->srtt = (utcp->srtt * 7 + rtt) / 8;
-		utcp->rto = utcp->srtt + max(utcp->rttvar, CLOCK_GRANULARITY);
 	}
 
+	utcp->rto = utcp->srtt + max(4 * utcp->rttvar, CLOCK_GRANULARITY);
+
 	if(utcp->rto > MAX_RTO) {
 		utcp->rto = MAX_RTO;
 	}