[CCID 3]: Use initial RTT sample from SYN exchange
The patch follows the following recommendation made in an erratum to RFC 4342:
"Senders MAY additionally make use of other available RTT measurements,
including those from the initial Request-Response packet exchange."
It implements larger initial windows with regard to this inital RTT measurement,
using the mechanism suggested in draft-ietf-dccp-rfc3448bis, section 4.2.
Signed-off-by: Gerrit Renker <gerrit@xxxxxxxxxxxxxx>
---
net/dccp/ccids/ccid3.c | 23 ++++++++++++++++-------
1 file changed, 16 insertions(+), 7 deletions(-)
--- a/net/dccp/ccids/ccid3.c
+++ b/net/dccp/ccids/ccid3.c
@@ -337,15 +337,24 @@ static int ccid3_hc_tx_send_packet(struc
hctx->ccid3hctx_t_last_win_count = now;
ccid3_hc_tx_set_state(sk, TFRC_SSTATE_NO_FBACK);
- /* Set initial sending rate X/s to 1pps (X is scaled by 2^6) */
ccid3_hc_tx_update_s(hctx, skb->len);
- hctx->ccid3hctx_x = hctx->ccid3hctx_s;
- hctx->ccid3hctx_x <<= 6;
- /* First timeout, according to [RFC 3448, 4.2], is 1 second */
- hctx->ccid3hctx_t_ipi = USEC_PER_SEC;
- /* Initial delta: minimum of 0.5 sec and t_gran/2 */
- hctx->ccid3hctx_delta = TFRC_OPSYS_HALF_TIME_GRAN;
+ /*
+ * Use initial RTT sample when available: recommended by erratum
+ * to RFC 4342. This implements the initialisation procedure of
+ * draft-ietf-dccp-rfc3448bis, section 4.2. X is scaled by 2^6.
+ */
+ if (dp->dccps_syn_rtt) {
+ ccid3_pr_debug("SYN RTT = %uus\n", dp->dccps_syn_rtt);
+ hctx->ccid3hctx_rtt = dp->dccps_syn_rtt;
+ hctx->ccid3hctx_x = rfc3390_initial_rate(sk);
+ hctx->ccid3hctx_t_ld = now;
+ } else {
+ /* Fall back to RFC 3448: set X/s initially to 1pps */
+ hctx->ccid3hctx_x = hctx->ccid3hctx_s;
+ hctx->ccid3hctx_x <<= 6;
+ }
+ ccid3_update_send_interval(hctx);
/* Set t_0 for initial packet */
hctx->ccid3hctx_t_nom = now;
-
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