So, at least how many Session Managers are needed?

A customer wants to migrate to a SIP relay and has a mobile demand. Each of their SIP trunks has nine users, and they want 30% of users to be able to use mobile devices at any times. There are now 9,000 SIP users. After discussion, they want each user to use three devices at the same time.

So, at least how many Session Managers are needed?
A . 1 Session Manager
B . 2 Session Managers
C . 3 Session Mangers
D . 4 Session Managers

Answer: B