: Provide fallback RTT value when none is available
PATCH 10/43 : Provide fallback RTT value when none is available
[DCCP]: Provide fallback RTT value when none is available
This implements RFC 4340, section 3.4:
"Each DCCP implementation thus defines a default round-trip time
for use when no estimate is available. This parameter should default to not less than 0.2 seconds [...]."
In addition, after consulting with a few TCP experts, the over-cautious upper bound of 4 seconds for an RTT sample has now been reduced to 3 seconds: to match the initial TCP RTO value as specified in [RFC 1122, 4.2.3.1].
Signed-off-by Gerrit Renker <[email protected]>
--- net/dccp/dccp.h | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-)
net/dccp/dccp.h +5 -2
@@ -73,9 +73,12 @@ extern void dccp_time_wait(struct sock *#define DCCP_RTO_MAX ((unsigned)(120 * HZ))/* FIXME: using TCP value */ -/* bounds for sampled RTT values from packet exchanges (in usec) */ +/* +* RTT sampling: sanity bounds and fallback RTT value from RFC 4340, section 3.4 +*/ #define DCCP_SANE_RTT_MIN 100 -#define DCCP_SANE_RTT_MAX (4 * USEC_PER_SEC) +#define DCCP_FALLBACK_RTT (USEC_PER_SEC / 5) +#define DCCP_SANE_RTT_MAX (3 * USEC_PER_SEC)/* Maximal interval between probes for local resources. */ #define DCCP_RESOURCE_PROBE_INTERVAL ((unsigned)(HZ / 2U))
Quoted 2 lines · Gerrit Renker
[DCCP]: Provide fallback RTT value when none is available
Acked-by Ian McDonald <[email protected]>
Signature · 3 lines
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