[lwip-devel] [bug #57976] TCP data communication broken due to ACK transmission delay

[Praveen Kumar]

URL:
  <https://savannah.nongnu.org/bugs/?57976>

                 Summary: TCP data communication broken due to ACK 
transmission delay
                 Project: lwIP - A Lightweight TCP/IP stack
            Submitted by: praveen_embedded
            Submitted on: Mon 09 Mar 2020 10:41:34 AM UTC
                Category: IPv4
                Severity: 3 - Normal
              Item Group: Faulty Behaviour
                  Status: None
                 Privacy: Public
             Assigned to: None
             Open/Closed: Open
         Discussion Lock: Any
         Planned Release: None
            lwIP version: 2.0.3

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Details:

Hi ,
we are using LWIP 2.0.3 for one of our project to establish the TCP connection
from ECU and Atmel micro.
We got the LWIP from atmel itself and i have modified little to support VLAN
data receive and transmit.
But now we are seeing some issue during data transmission.
When the ECU goes to sleep, it cut down the Ethernet link and when it wakes up
it will establish the Ethernet connection.
But here when the ECU wakes up the communication is not going well from our
LWIP stack. We are seeing multiple re transmissions which are causing issues
in data transmission.
I have seen new behavior like when i received new frame on TCP, i am trying to
ACK back using ACK now function(pcb->prio =
TCP_PRIO_MAX;tcp_ack_now(pcb);tcp_send_empty_ack(pcb);tcp_output(pcb);), but i
am seeing the ACK packet after my data packet is been transferred.
This i didn't understand like why the ACK packet is transferred after data
packet? this is also one of the reason for us to see communication failure.
Can someone please help me here that how to send ACK immediately after
receiving the TCP packet(currently my data packets are sent out every 10ms
once and the ACK is transmitted after data packet is being sent out). Please
let know how to send ACK immediate, currently we are stuck here and our
communication is not proper.
I am attaching the images for our communication issues.
Here LWIP_IP: 192.168.6.182
     ECU IP : 192.168.6.144
If you see LWIP_TCP_DataSentoutFirst.JPG, the data is send first and ACK is
sent after that even though the ACK transmission is initiated first with
priority level set to MAX.

Thanks & Regards,
PraveenKumar.



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File Attachments:


-------------------------------------------------------
Date: Mon 09 Mar 2020 10:41:34 AM UTC  Name: LWIP_TCP_DataSentoutFirst.JPG 
Size: 121KiB   By: praveen_embedded

<http://savannah.nongnu.org/bugs/download.php?file_id=48564>
-------------------------------------------------------
Date: Mon 09 Mar 2020 10:41:34 AM UTC  Name: LWIPCommunicationIssue.JPG  Size:
296KiB   By: praveen_embedded

<http://savannah.nongnu.org/bugs/download.php?file_id=48565>

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