Re: [lwip-users] tcp_write function merges 2 different packets while sending

[Rod Boyce]

On 21/12/2019 08:53, goldsimon wrote:
>
> Urvi wrote:
>> [..]
>>
>> But when I send 1 data packet of size=6 bytes (call tcp_write() and
>> then
>> tcp_output()) and next packet of size=45 bytes (call tcp_write() and
>> then
>> tcp_output()), then at server side it receives as a one single data
>> packet
>> of size=51 bytes; due to this my complete data packet becomes garbage
>> and I
>> got failure in communication. (this is just one packet example, but it
>> happens often).
>>
>>
>> How to solve this issue?
> That's expected TCP behaviour, not an lwIP issue. Of you need datagrams 
> strictly separated, use UDP.
>
> Regards,
> Simon
>
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TCP is a streaming protocol this means that packets can be joined
together either at the sender or the receiver.

UDP will keep the packets separate but sending a 6 byte packet is very
inefficient over Ethernet. 

The minimum Ethernet packet size is 64-bytes, if you are the protocol
owner I would suggest some sort of packet ageration to merge smaller
packets and make for a more efficient transfer over Ethernet.


Rod