Commit 30833ffe authored by Gerrit Renker's avatar Gerrit Renker Committed by David S. Miller
Browse files

[CCID3]: 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: default avatarGerrit Renker <gerrit@erg.abdn.ac.uk>
Signed-off-by: default avatarIan McDonald <ian.mcdonald@jandi.co.nz>
Signed-off-by: default avatarArnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 89560b53

net/dccp/ccids/ccid3.c

+21 −10
Original line number Diff line number Diff line
@@ -334,19 +334,30 @@ static int ccid3_hc_tx_send_packet(struct sock *sk, struct sk_buff *skb) 
				usecs_to_jiffies(TFRC_INITIAL_TIMEOUT)));

		hctx->ccid3hctx_last_win_count	 = 0;

		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) */

		hctx->ccid3hctx_x = hctx->ccid3hctx_s = skb->len;

		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;



		/* Set t_0 for initial packet */

		hctx->ccid3hctx_t_nom = now;



		hctx->ccid3hctx_s = skb->len;



		/*

		 * Use initial RTT sample when available: recommended by erratum

		 * to RFC 4342. This implements the initialisation procedure of

		 * draft rfc3448bis, section 4.2. Remember, 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 {

			/* Sender does not have RTT sample: X = MSS/second */

			hctx->ccid3hctx_x = dp->dccps_mss_cache;

			hctx->ccid3hctx_x <<= 6;

		}

		ccid3_update_send_interval(hctx);



		ccid3_hc_tx_set_state(sk, TFRC_SSTATE_NO_FBACK);

		break;

	case TFRC_SSTATE_NO_FBACK:

	case TFRC_SSTATE_FBACK:

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