hi, all: I implemented ppp protocol on lpc2138, the modem is GPRS modem. The server send udp data to modem fastly, Some times, the datas modem gived to cpu lost the char "7E".when it's occured,the protocol can not handle all the next datas. I will close the option UDP_OPT_SEND_CS and UDP_OPT_CHK_CS.Is this effectively? Thanks!