Re: [lwip-users] Debug pppos packet loss issue

[Patrick Klos]

On 3/2/2017 8:10 AM, Sylvain Rochet wrote:
> Hi Axel,
>
> On Thu, Mar 02, 2017 at 08:55:15PM +0800, Axel Lin wrote:
> > Hi,
> > I'm using current lwIP master tree.
> >
> > I got my device connect to internet via 4G/LTE module now (by PPPoS).
> > However, I found sometimes download file size mismatch when
> > try to download some files (about 100KB) from http server.
> >
> > I tried enable PPP_DEBUG / PRINTPKT_SUPPORT / PPP_PROTOCOLNAME /
> > LWIP_STATS_DISPLAY, but I don't see any unusual things.
> >
> > The only strange thing is in download success case, the download speed
> > is fast. In download file mismatch (seems some packet lost) case, the
> > download speed is very low. Any hint to debug such issue?
> HTTP uses TCP so whatever happens you shouldn't have a size mismatch.

I was thinking the same thing.  If you get to the end of the HTTP 
download with a file, then the network communications via TCP is 
(probably) not responsible for the corrupt file.  That implies that your 
app that collects the pieces of the file from the network and writes 
them down may have a problem instead.

Add to that the fact that the transfer takes a lot longer when the file 
is corrupt, and knowing that LwIP has rules about what can be called 
when and in which context, it seems probable that your app's use of LwIP 
is not quite right and causing the network errors that are resulting in 
the problems you're seeing.

Do you have a packet trace of the HTTP download?  That will likely have 
clues about what's going on

Patrick