Re: [lwip-users] Send out TCP packet asap?

[Simon Goldschmidt]

Chen <address@hidden> wrote:
> I use lwip_send (....0), along with FreeRTOS on AVR32, to send out TCP
> packets
> 
> Each time I call, I present 200 bytes to lwip. From Wireshark, I can 
> see the packets size alternating between 200 and 1400 bytes with more 
> idle time right before the 1400-byte packet
> 
> Is there a flag I can set so that lwip sends out the packet (200 
> bytes) if the output queque is empty, without trying to packaging the 
> data to make it more efficient?

It is efficient as it is, as it uses less header bytes per data byte when 
combining multiple 200-byte-chunks into one 1400-byte-packet. Note that this is 
only done when there is un-ACKed data - this is the TCP representation of your 
"output queue is empty". Note that when using sockets, the actual output queue 
is always empty as tcp_output() is called after each send().

What you want is less latency, I guess (i.e. sending the packets right away 
without combining them)? This can be achieved by disabling the nagle algorithm, 
which can be done like this on most socket implementations:


int flag = 1;
ret = setsockopt( sock, IPPROTO_TCP, TCP_NODELAY, (char *)&flag, sizeof(flag) );



Simon