[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 <gerrit@xxxxxxxxxxxxxx> --- net/dccp/dccp.h | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) --- a/net/dccp/dccp.h +++ b/net/dccp/dccp.h @@ -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)) - To unsubscribe from this list: send the line "unsubscribe dccp" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
