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

[Jon Bean]

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.

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?

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

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.

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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