To provide firewall traversal, which components are needed?

To provide firewall traversal, which components are needed?

A.
2 Cisco TelePresence Video Communication Server Controls

B.
1 Cisco TelePresence Video Communication Server Control 2 Cisco TelePresence Video Communication Server Expressways

C.
2 Cisco TelePresence Video Communication Server Expressways

D.
1 Cisco TelePresence Video Communication Server Control 1 Cisco TelePresence Video Communication Server Expressway