[S1] VoIP stands for 'Voice over IP'. Thus the voice media is always carried over IP, but signaling may be done via circuit switched means  -  False True

[S2] The difference between IP Telephony and VoIP is that IP Telephony media is not limited to Voice. The signaling however for both IP Telephony and VoIP is basically the same  -  False True

[S3] Jitter is the variation in packet loss  - FalseTrue

[S4] Diffserv  is a QoS technique, which enables treating packets differently on the fly, i.e. with Diffserv apriori agreement or/and resource reservation is not required  - False True

[S5] Even two circuit switched users using their POTS (Plain Old Telephone Service) phones may still be involved in a VoIP call  -  False True