I work on rtl-tcp over ppp protocol. First gsm modüle is given IP by AT commands and then is connected ethernet over ppp protocol. At software , tcp socket is opened and tcp_send function is worked over ppp . RTL TCPNet is working very well. After a while, worked RL-Tcpnet over ppp protocol goes down and timeout. Debug screen always shows this error which is "000.0 TCP-ERR:Send, Socket 1 reentrant callback". Would to be the reason why ethernet go down and timeout?