Re: [lwip-users] Sending a large amount of data using UDP

[Patrick Klos]

On 7/19/2020 10:27 AM, Jon Bean wrote:
> Hi Patrick
>
> Yes I did try with fragmentation enabled but that didn't seem to work. 
> I can see in wireshark that there is a packet with IP4 type that 
> mentions fragmentation , but I don't get any UDP packets.

Does Wireshark reassemble the fragments into a whole 4K UDP packet? Are 
you willing/able to share the Wireshark trace file (.pcap)?

> I also did a test where I just send two packets of 1400, one after 
> another, but only one get sent. I am wondering if I need to check some 
> send buffer like in TCP?

I've had no problem using UDP reliably on the TIVA with LwIP.  Did you 
allocate enough buffers?

> If I just allocate a pbuf of 2800 and then send it I dont actually get 
> any errors, it just doesnt send anything.

Unless fragmentation was enabled, that's not going to get very far.

> The problem is that I cant really do anything with the data in terms 
> of adding sequence numbers, as I am developing the code for the TIVA 
> for a pc application that is already defined. I kind of thought that 
> UDP could send up to 64k. I am a bit surprised I cant just ask LWIP to 
> send a large amount of data and then it send multiple packets.

So the receiver is already expecting a 4K UDP packet?  That kind of ties 
your hands, but I'm (pretty) sure you can get it to work with LwIP on 
the TIVA*.

Patrick

* I don't think I've ever actually use IP fragmentation on the TIVA, but 
I'm sure it works (and if it doesn't, it can be debugged and fixed - 
it's not that complicated)

> Regards
>
> Jon
>
>
> On 19/07/2020 15:18, Patrick Klos wrote:
> > On 7/19/2020 6:44 AM, Jon Bean wrote:
> > > Hi
> > >
> > > I have an application were I need to send around 4k of data using 
> > > UDP. What I would like to know is how I go about sending this using 
> > > LWIP. I can send small packets no problem. I first allocate a pbuf. 
> > > Then copy my data to the pbuf. Then send the data. But sending 4k of 
> > > data doesnt work. I realise that the Ethernet has a max payload of 
> > > 1500 bytes. Is there a different way to send large amounts of data? 
> > > Do I need to configure something and then do it the same way I have 
> > > previously? I am using a embedded TIVA micro controller.
> > >
> > > Thanks
> > >
> > > Jon
> >
> > Have you enabled IP fragmentation? (IP_FRAG)
> >
> > Or you could just break up the data yourself, add a little custom 
> > header, and essentially fragment the data yourself. Depending on 
> > what's in this data, you could add sequence numbers and a way for the 
> > peer to report they missed a chunk?  How often are you sending these 
> > blocks of data?
> >
> > Patrick
> >
> >
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