Re: [lwip-users] TCP ACK Problem?

[Bill Auerbach]

Doesn’t it make sense to update to 1.4.1 before asking about a bug or problem?

 

From: address@hidden [mailto:address@hidden On Behalf Of Rodrigo Garbi
Sent: Tuesday, August 27, 2013 9:29 AM
To: address@hidden
Subject: Re: [lwip-users] TCP ACK Problem?

 

Anyone?

 

 

2013/8/23 Rodrigo Garbi <address@hidden>

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!