Why do I get random packets from my ISP?

[brakedown307]

Hello!

I have a router with a SIM card and a mobile connection and recently I did an experiment:

• 
  I did a factory reset;
  set up my mobile connection;
  enabled tcpdump logging;
  rebooted the router so that the RX/TX packet count would be reset;
  disconnected all devices from the router;
  left the router running overnight;
  checked the tcpdump file the next morning;

I discovered that the router was communicating mostly with one IP address, which I Googled and found that it belongs to my SIM card's ISP. Does anyone know why this happens? What is the purpose of this communication between my SIM card and my ISP?
Here's a screenshot of a portion of my tcpdump file:
http://imgur.com/a/zNpxv
I put red bars over my IP since it's a static public IP address and the card belongs to my employers, but the IP in question is 88.119.152.93. It was pretty easy to find that it belongs to my ISP, so it's nothing malicious, but my question is:
What is the purpose of this back and forth communication?

 

[brakedown307]

Solved the problem. Turns out this was happening because of my static public IP address. Deleted the APN and now it doesn't send or receive packets.