Design an On-Call Escalation System

Question Description:

Design an On-call Escalation System. The levels of employees handling oncall - Developer, Manager and Director. Initial ticket always goes to a developer. If a developer is not able to handle the ticket or no developer is available, ticket gets escalated to a manager. Similarly, if no manager is available or a manager is not able to resolve the ticket, it gets escalated to director. If no one is available to take the ticket, it goes into a pending queue.

This is a combination of Product and System Design, not really too much into scalability.