Hi all,
I met some problems when studying the following section of source code, which
is about the behavior of a TFRC receiver:
static void ccid3_hc_rx_packet_recv(struct sock *sk, struct sk_buff *skb)
{
.
993 ins = dccp_rx_hist_add_packet(ccid3_rx_hist, &hcrx->ccid3hcrx_hist,
&hcrx->ccid3hcrx_li_hist, packet);
if (DCCP_SKB_CB(skb)->dccpd_type == DCCP_PKT_ACK)
return;
999 switch (hcrx->ccid3hcrx_state) {
case TFRC_RSTATE_NO_DATA:
.
return;
1008 case TFRC_RSTATE_DATA:
hcrx->ccid3hcrx_bytes_recv += skb->len -
dccp_hdr(skb)->dccph_doff * 4;
1011 if (ins != 0)
1012 break;
dccp_timestamp(sk, &now);
if (timeval_delta(&now, &hcrx->ccid3hcrx_tstamp_last_ack) >=
hcrx->ccid3hcrx_rtt) {
hcrx->ccid3hcrx_tstamp_last_ack = now;
ccid3_hc_rx_send_feedback(sk);
}
return;
default:
.
return;
}
/* Dealing with packet loss */
.
1032 ccid3_hc_rx_detect_loss(sk);
p_prev = hcrx->ccid3hcrx_p;
/* Calculate loss event rate */
if (!list_empty(&hcrx->ccid3hcrx_li_hist))
/* Scaling up by 1000000 as fixed decimal */
hcrx->ccid3hcrx_p = 1000000 /
dccp_li_hist_calc_i_mean(&hcrx->ccid3hcrx_li_hist);
if (hcrx->ccid3hcrx_p > p_prev) {
ccid3_hc_rx_send_feedback(sk);
return;
}
}
According to RFC 3448 section 6.1,
"When a data packet is received, the receiver performs the following steps:
1) Add the packet to the packet history.
2) Let the previous value of p be p_prev. Calculate the new value of p as
described in Section 5.
3) If p > p_prev, cause the feedback timer to expire, and perform the
actions described in Section 6.2
If p <= p_prev no action need be performed."
To my way of thinking, the step 1 is done in line 993. However, the step 2 and
3 have no chance to be done in most cases: in the switch process starting from
line 999, the only possibility to jump out to the "p" calculation (line 1032)
is the variable "ins" is not be 0 (line 1011 and 1012). But ins=1 only happens
when unordered packet is received. This is quite different from what RFC says.
What's wrong in my analysis?
Thank you.
Regards,
Zhou Bin
-
To unsubscribe from this list: send the line "unsubscribe dccp" in
the body of a message to [EMAIL PROTECTED]
More majordomo info at http://vger.kernel.org/majordomo-info.html
