To provide firewall traversal, which components are needed?

To provide firewall traversal, which components are needed?

A.
Cisco TelePresence Video Communications Server Control and 2 Cisco TelePresence Video Communications Server Expressways

B.
Cisco TelePresence Video Communication Server Control and 1 Cisco TelePresence Video Communication Server Expressway

C.
2 Cisco TelePresence Video Communication Server Expressways

D.
2 Cisco TelePresence Video Communication Server Controls