GPRS serial port programming in linux

For GPRS serial port programming in linux-General Linux technology-Linux programming and kernel information, see the following for details. I encountered a problem during GPRS development over the past few days. the serial communication program I wrote can communicate with super terminals on XP. I sent a string to xp through the development board: ATD15170476687; super keys on XP will print this string. In the same program, I connected the Development Board to GPRS using a serial line, and then ran the program. GPRS did not respond.
I connected GPRS directly to the PC using a serial cable, and then I sent it via the terminal opened on XP: ATD15170476687; GPRS would call this phone.
Why is it like this? the same command string only produces different objects. Why does GPRS fail to accept it?
To sum up, the above consciousness GPRS and arm development boards can communicate with PCs through serial ports, but the GPRS and ARM development boards cannot communicate with each other.

Could you please help me see what the problem is? thank you.