Re: [lwip-users] TCP ACK Problem?

[Rodrigo Garbi]

Hi!

Thank you Bill and Chauveau for your answers. Firstly I would like to solve the problem running LwIP 1.4.0, or at least to understand a little more about it; then, if no solution arises, I would try with LwIP 1.4.1.

Chauveau, device A transmits one data packet that won´t be acknowledged by my board running LwIP, and then it will transmit another 3 data packets, until it is aware of need of retransmission. Then, it will retransmit only the first two data packets (instead of four) and my board will acknowledge the 4 data packets. But the problem is that at application level I only get the first two data packets... That´s why I say I lose two data packets.

IP_REASSEMBLY is activated and IP_REASS_MAX_PBUFS is set to 16. 

But, I don´t think it´s related to that, because data packets are only 9-bytes long.

--

 

2013/8/27 Chauveau Wilfried <address@hidden>

Hello,
I'm not that pro in TCP/IP communication but it seems that only 1 packet is lost.
When A retransmit the missing one plus some more data, your board is finally able to rebuild the stream and continue acknowledging all received data. A does not retransmit the last 18 bytes because they have been successfully received & acknowledged.
Is IP_REASSEMBLY activated and how big is your

IP_REASS_MAX_PBUFS ?
Except for the part where you lose a packet, the flow does not seems to me that buggy.

--

Le 23/08/2013 22:30, Rodrigo Garbi a écrit :

Hi!

I'm working with FreeRTOS v7.0.1 and LwIP 1.4.0 and I'm facing the following problem:

Device A and B transmit data every 40 ms to my board (where I'm running LwIP) and once in a while I can notice some data from device A is being missed.

So I did some research with CommView and found that:

1) Device A sends data (9 bytes length) to my board and get correct ACK from it:

Sequence: 0x13D5388C (332740748)

 

Acknowledgement: 0x00001A57 (6743)

Response from my board:

Sequence: 0x00001A57 (6743)
Acknowledgement: 0x13D53895 (332740757)

 

2) Device A send 9-bytes data to my board, but this won´t ACK:

Sequence: 0x13D5389E (332740766)

Acknowledgement: 0x00001A57 (6743)

Sequence: 0x00001A57 (6743)
Acknowledgement: 0x13D5389E (332740766)

3)Device A does not care about it (maybe because data is already in ethernet transceiver buffer) and sends a new data (9-bytes); my board will not ACK it:

Sequence: 0x13D538A7 (332740775)

Acknowledgement: 0x00001A57 (6743)

Sequence: 0x00001A57 (6743)

Acknowledgement: 0x13D5389E (332740766)

4)Same as 3

Sequence: 0x13D538B0 (332740784)

Acknowledgement: 0x00001A57 (6743)

Sequence: 0x00001A57 (6743)
Acknowledgement: 0x13D5389E (332740766)

5) Same as 3

Sequence: 0x13D538B9 (332740793)

Acknowledgement: 0x00001A57 (6743)

Sequence: 0x00001A57 (6743)
Acknowledgement: 0x13D5389E (332740766)

6) Finally, device A is aware of the problem and retransmits data, but instead of transmitting 36 bytes (9 x 4), only transmits 18 bytes

Sequence: 0x13D5389E (332740766)

Acknowledgement: 0x00001A57 (6743)

Data length: 0x12 (18)

    

And my board running Lwip 1.4.0 will acknowledge 36 bytes instead of 18:

Sequence: 0x00001A57 (6743)
Acknowledgement: 0x13D538C2 (332740802)

So device A won´t transmit last two 9-bytes packets, and they will be lost!

Anyone can help me with this? Is it a bug in LwIP or what is happening?

Thank you!

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