STUN is for signaling, but the hole-punching business is not 100% guaranteed to work, so you need TURN as the back up relay server. DTLS is needed for both p2p

STUN is for signaling, but the hole-punching business is not 100% guaranteed to work, so you need TURN as the back up relay server. DTLS is needed for both p2p traffic and the replaying traffic through TURN, so your TURN server does need DTLS for its job.