Which of the following are functions that are often provided by an ITSP but are not typically  provided by the PSTN？（）

A. device PoE requirements
B. device IP address
C. device voice VLAN ID
D. device platform

A. an edge port that transitions to the forwarding state
B. a non-edge port that transitions to the blocking state
C. a non-edge port that transitions to the forwarding state
D. an edge port that transitions to the blocking state
E. any port that transitions to the blocking state
F. any port that transitions to the forwarding state

A. active
B. speak
C. learn
D. listen
E. init
F. standby