[lwip-users] Slow sending speed

[Sebastian]

Hello,

as the title already says, I've got a problem with the sending speed, which is 
extremly slow. My  platform is a LPC2468 Controller from NXP with an ARM 
Core.
It seems the problem is that lwIP sometimes holds back packets and waits for 
the next ACK of the packet just sent. According to a typical TCP session, the 
remote station expects a second packet and waits for 200ms before it's sends 
the ACK. After that, lwIP will send the next packets.

Here is the log of Wireshark:

  No.  Time       Source    Dest.   Protocol  Info
  2873 0.220744   lwIP      .net       ESP    ESP (SPI=0x0e0e0e0e)
  2874 0.221078   lwIP      .net       ESP    ESP (SPI=0x0e0e0e0e)
  2875 0.221095   .net      lwIP       TCP    udt_os > ndmp [ACK] Seq=1048577 
Ack=515073 Win=65535 Len=0
  2876 0.221912   lwIP      .net       ESP    ESP (SPI=0x0e0e0e0e)
  2877 0.353007   lwIP      .net       ESP    ESP (SPI=0x0e0e0e0e)
  2878 0.353065   .net      lwIP       TCP    udt_os > ndmp [ACK] Seq=1048577 
Ack=517121 Win=65535 Len=0
  2879 0.353277   lwIP      .net       ESP    ESP (SPI=0x0e0e0e0e)
  2880 0.546842   .net      lwIP       TCP    udt_os > ndmp [ACK] Seq=1048577 
Ack=518145 Win=65535 Len=0
  2881 0.547778   lwIP      .net       ESP    ESP (SPI=0x0e0e0e0e)
  2882 0.548066   lwIP      .net       ESP    ESP (SPI=0x0e0e0e0e)
  2883 0.548089   .net      lwIP       TCP    udt_os > ndmp [ACK] Seq=1048577 
Ack=520193 Win=65535 Len=0
  2884 0.548904   lwIP      .net       ESP    ESP (SPI=0x0e0e0e0e)
  2885 0.549227   lwIP      .net       ESP    ESP (SPI=0x0e0e0e0e)
  2886 0.549244   .net      lwIP       TCP    udt_os > ndmp [ACK] Seq=1048577 
Ack=522241 Win=65535 Len=0
  2887 0.550089   lwIP      .net       ESP    ESP (SPI=0x0e0e0e0e)
  2888 0.765583   .net      lwIP       TCP    udt_os > ndmp [ACK] Seq=1048577 
Ack=523265 Win=65535 Len=0
  2889 0.766469   lwIP      .net       ESP    ESP (SPI=0x0e0e0e0e)
  2890 0.766782   lwIP      .net       ESP    ESP (SPI=0x0e0e0e0e)
  2891 0.766801   .net      lwIP       TCP    udt_os > ndmp [ACK] Seq=1048577 
Ack=525313 Win=65535 Len=0
  2892 0.767610   lwIP      .net       ESP    ESP (SPI=0x0e0e0e0e)
  2893 0.767943   lwIP      .net       ESP    ESP (SPI=0x0e0e0e0e)
  2894 0.767960   .net      lwIP       TCP    udt_os > ndmp [ACK] Seq=1048577 
Ack=527361 Win=65535 Len=0
  2895 0.768778   lwIP      .net       ESP    ESP (SPI=0x0e0e0e0e)
  2896 0.846978   lwIP      .net       ESP    ESP (SPI=0x0e0e0e0e)
  2897 0.847028   .net      lwIP       TCP    udt_os > ndmp [ACK] Seq=1048577 
Ack=529409 Win=65535 Len=0
  2898 0.847265   lwIP      .net       ESP    ESP (SPI=0x0e0e0e0e)
  2899 0.984325   .net      lwIP       TCP    udt_os > ndmp [ACK] Seq=1048577 
Ack=530433 Win=65535 Len=0
  2900 0.985204   lwIP      .net       ESP    ESP (SPI=0x0e0e0e0e)
  2901 0.985516   lwIP      .net       ESP    ESP (SPI=0x0e0e0e0e)
  2902 0.985535   .net      lwIP       TCP    udt_os > ndmp [ACK] Seq=1048577 
Ack=532481 Win=65535 Len=0


Here are the options I used:

#define TCP_WND                 2048
#define TCP_MSS                 1024

#define MEMP_NUM_PBUF   32
#define PBUF_POOL_SIZE          32
#define MEMP_NUM_TCP_SEG        32

#define TCP_SND_BUF             2048
#define TCP_SND_QUEUELEN        (16 * (TCP_SND_BUF/TCP_MSS)) * 2
#define TCP_SNDLOWAT            1024


Maybe someone has an idea.

Greetings, Sebastian