In voice$-$over$-$IP systems, select possible answer$($s$)$

Group of answer choices

Jitter is a major problem in real$-$time traffic because of the delay variation of the communicated packets

A main problem in peer$-$to$-$peer VoIP system is that the users are usually hidden behind a network address translator

Skype and similar peer$-$to$-$peer applications use helping nodes with public IP address to establish the connection between the peers.

Voice$-$over$-$IP systems can only use TCP protocol