[lwip-users] Retransmit too quick?

[Xun Chen]

Hi all,

I ran into a problem with lwip 1.4.1. For some reason, lwip decides to 
retransmit package immediately, without waiting for the ACK for the receiver

The Wireshark captures for the moment (16KB only) can be downloaded from

https://www.dropbox.com/s/zr4b4qo9c9tp20m/AckTooQuick.pcapng?dl=0

(The above capture is tiny part of a huge capture of many MBs lwip 
transferred without any trouble, the data rate is 200KB/sec)

Here you can see, the PC acks lwip TCP transfer properly (one Ack for 
every two TCP packets), untile packet #17, lwip decides to retransmit 
packet #16 immediately (only 0.3ms after #16 is transmitted).

Can anyone shine me some light on this? such as any possible mistakes in 
my lwip configuration, program flow, or error handling, etc?

Thanks for any pointer.

Chen