Re: [lwip-users] What are LwIP TCP max transfer rates and how can I optimize them?

[Blue]

Jonathan Larmour schrieb:
> Blue wrote:
>   
> > Hello to everybody,
> >
> > For my final exam I have to realise a connection between a PC and a
> > camera via TCP/IP. On the camera the LwIP Stack (Version 1.1.1) is
> > embedded. It is the first time, that I work with LwIP.
> >
> > At the moment I have realized the connection with the low-level “callback”
> > API, the higher-level “sequential” API can not be used on the camera.
> > I’m able to transmit pictures from the camera to the PC, but it is not
> > fast enough. I can transmit four frames in a second (compiles about 53
> > MBit/s). The camera and the PC have a 1000 Mbit/s Ethernet Port, so that
> > this is fast enough. When I send only text data as fast as possible the
> > maximal transfer rate is 86 Mbit/s and I need around 160 Mbit/s to get a
> > usable result.
> > Has anybody experiences with transfer rates and knows which transfer rates
> > are possible with the LwIP TCP Stack and which parameter is relevant to
> > get the transmission faster?
> >     
>
> Assuming you've got enough memory, optimise your TCP MSS to what will fit
> in the MTU. Increase the window size as large as you can. Enable lwIP's
> statistics and see if it's running out of any resources. Do packet sniffing
> to see if you can find any abnormal delays.
>
> Does your ethernet driver copy packets? Maybe for your application you may
> wish to try doing zero-copy packets (assuming your ethernet MAC can DMA).
>
> Ultimately, some hardware (CPU, memory bus, ethernet MAC) simply isn't fast
> enough to drive things over the wire fast enough. You may have already hit
> the limit with your hardware.
>
> Jifl
>   

Thank you for your answer. The problem is, that I can not change the TCP 
MSS because LwIP is implemented on the camera by the manufacturer. That 
is why I can not change all parameters on my own. I only have the chance 
to ask the manufacturer to change things when I know, that this would be 
optimize the performance.

I made a test with the UDP protocol. I have change continuously the pbuf 
size in the moment I’m able to send data. First it stops by a pbuf size 
of 1460 where I get a transfer rate of 14 frames per second. Than I 
changed the network card of the PC the Jumbo Frames to 9014 so I get 
transfer rats of 35 frames per second. So I would say the hardware is 
not the problem. Or are there differences between the hardware used for 
UDP and that for TCP?

Here are some parameters where I would think they are important:

MEM_SIZE                     0x8000
TCP_MSS                      1460
TCP_SND_QUEUELEN             (4 * TCP_SND_BUF / TCP_MSS) --> 44
TCP_WND                      4096
TCP_MARTX                    12
TCP_SYNMAXRTX                4
MTU                          1500   (that value I can modify)

What do you think which values are the best to get the maximum data 
transfer?

Gregor