SIM900不能发送GPRS数据

最近在用ATK-SIM900A GSM/GPRS模块短信电话开发板调试，
，但是出现了一点问题，TCP方式下，无法发送数据，我用电脑串口调试工具向SIM900A模块发送AT指令，结果如下：
AT+CSQ
+CSQ: 26,0
OK
AT+CGCLASS="B"
OK
AT+CGDCONT=1,"IP","CMNET"
OK
AT+CGATT=1
OK
AT+CIPCSGP=1,"CMNET"
OK
AT+CLPORT="TCP","3001"
OK
AT+CIPSTART="TCP","115.159.185.143","7270"
OK
STATE: TCP CLOSED
CONNECT FAIL
AT+CIPSTART="TCP","115.159.185.143","7270"
OK
CONNECT OK
AT+CIPSEND
> 123456789123456789123456789123456789
123456789
123456789
123456789
123456789
始终 没有出现 SENK OK 的提示，同时在TCP服务器端也看不到数据。
请问这是怎么回事？谢谢！