Asterisk connect to SER

i am a student and i have a project to setup and configure system that

PSTN (phone call) ---- Asterisk (via SIP) ------ SER (i.e. any time
traffic is to be sent/received to/from PSTN, use Asterisk as GW)

Both SER and ASTERISK are in the same LAN.

Now, i can set SER server and Asterisk server completely.
but the problem is “How i connect SER and Asterisk together?”

Please give me the explanation or suggestion to setup.

Thank you very much.