multiple client socket connections issue w/ RTOS SDK

[独孤垂钓2003]

Hi,
I'm trying to use two client sockets to connect the remote server, one is for message/command communication while another one is used for OTA upgrade. These two sockets are using differnt port.

Now the problem is that, I can create both two sockets, connected to the remote server. But only one socket can write/recv packet, another one is blocked in socket write() function. I tried to modify some TCP related parameters in LWIP opt.h/lwipopt.h files and recompiled the liblwip.a, but seems not working yet.

I remember somewhere stated in ESP8266 documents saying there is only one client socket connection and four server scoket connections can be used. Could you please let me know where is the limitation for that implementation? something related with LWIP stack?

Could you please recommend how I can move on?

Thanks in advance!