While working on the promised EWMA patch for CCID 3 packet sizes, I stumbled over two things
and can make no sense of a bit of CCID 3 Receive code:
1) ccid3_hc_rx_sock maintains a real-timer RTT counter ccid3hcrx_rtt
which is an alias for a TFRC structure defined in <linux/tfrc.h>
2) ccid3_hc_rx_packet_recv (detailed below) updates this, but leaves the variable
`win_count = packet->dccphrx_ccval;' entirely untouched after initialisation
It may be that ... ?
* this is because a real-time counter as opposed to the 4-digit window value
counter affords better reliability (but then win_count should be removed)
* this stems from the original TFRC code and might need update
I'd be glad for clarification about this code:
static void ccid3_hc_rx_packet_recv(struct sock *sk, struct sk_buff *skb)
{
/* ... */
switch (DCCP_SKB_CB(skb)->dccpd_type) {
case DCCP_PKT_ACK:
if (hcrx->ccid3hcrx_state == TFRC_RSTATE_NO_DATA)
return;
case DCCP_PKT_DATAACK:
/* ... */
rtt_prev = hcrx->ccid3hcrx_rtt;
/* ... */
r_sample = timeval_usecs(&now);
t_elapsed = opt_recv->dccpor_elapsed_time * 10;
/*
after updating r_sample with regard to t_elapsed ...
==> The code that now follows is identical with ccid3_hc_tx_packet_recv
--is this a leftover ?
--should it not rather update the sending structure (ccid3hctx_rtt)
==> why not use win_count ??
*/
if (hcrx->ccid3hcrx_state == TFRC_RSTATE_NO_DATA)
hcrx->ccid3hcrx_rtt = r_sample;
else
hcrx->ccid3hcrx_rtt = (hcrx->ccid3hcrx_rtt * 9) / 10 +
r_sample / 10;
/* ... */
break;
case DCCP_PKT_DATA:
break;
default: /* We're not interested in other packet types, move along */
return;
}
/* ... */
win_count = packet->dccphrx_ccval; /* XXX this is the only place `win_count' appears */
/* ... */
}
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