Ceragon Networks interview questions

1, design a communication system for Pelofonia so that each user should receive an IP address and a certain type of service (gold, silver and normal subscription), according to the type of subscription we will know what privileges the user can receive Literally the data structure and the following operations - IP assignment to a new user - Finding an existing user - Deleting an existing user. What are the costs for each action? 2, Now there are several threads running on the above system, what could be the problems that will arise