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

[Axel Lin]

Hi Patrick,

2017-03-02 21:21 GMT+08:00 Patrick Klos <address@hidden>:
> 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.

The problem is I don't get any error code while download the file.
Only compare the download size then I know it's incorrect.
(and sometimes it's correct)

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

Regarding "packet trace of the HTTP download" do you mean wireshark log?
I don't know how to capture the packet  sent/received via LTE.
Or do you mean get the packet trace by enable some debug options?

Thanks for your help,
Axel