[lwip-devel] [bug #63092] When the length of unack data is less than pcb->cwnd, LWIP cannot send packets.

[jiangheng]

URL:
  <https://savannah.nongnu.org/bugs/?63092>

                 Summary: When the length of unack data is less than
pcb->cwnd, LWIP cannot send packets.
                 Project: lwIP - A Lightweight TCP/IP stack
               Submitter: jinag12345
               Submitted: Fri 23 Sep 2022 10:14:28 AM UTC
                Category: TCP
                Severity: 3 - Normal
              Item Group: None
                  Status: None
                 Privacy: Public
             Assigned to: None
             Open/Closed: Open
         Discussion Lock: Any
         Planned Release: None
            lwIP version: 2.1.3


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Follow-up Comments:


-------------------------------------------------------
Date: Fri 23 Sep 2022 10:14:28 AM UTC By: jiangheng <jinag12345>
In tcp_output function:
if (lwip_ntohl(seg->tcphdr->seqno) - pcb->lastack + seg->len > wnd) {
    ....
    goto output_done;
}

In tcp_slowmgr function:
if (pcb->rtime >= pcb->rto) {
    pcb->cwnd = pcb->mss;
    tcp_rexmit_rto_commit(pcb);
}

tcp_rexmit_rto_commit ≈ tcp_output;

in tcp_output, The printf command output is as follows:
lwip_ntohl(seg->tcphdr->seqno) = 405161
pcb->lastack = 403701
seg->len = 1460
pcb->snd_wnd 65535
pcb->cwnd = 1460
so tcp_output will not send this tcp segment, It enters the slow start phase
of congestion control and cannot exit.
Although unack data exists, the value of snd_wnd is 65535. lwip cant send data
is correct this moment?








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