Web service for persistent SMPP polling?

Question

linux

There is such a task:
1. An SMS number works for a cellular operator, when receiving an SMS on this number, the operator sends a string with the number via an SMPP connection.
2. You need to make a web service that keeps a permanent SMPP connection to the server, receives responses and sends its requests.
In which direction to dig? Thoughts aside while towards demons and sockets.