SIP SIP standards for Session Initiation Protocol and It's Purely IP based. BRI/PRI PRI stands for Primary Rate Interface and It contains One 64Kbps T1 or E1 Chanel for Signaling AKA Channel D and 23 T1 or 30 E1 Channels as Bearing Chanel aka Channel B.\ BRI standards for Basic Rate Interface and Contain Two Barer channel and One Signaling Chnnel AKA 2B+D. Further Both Both PRI and BRI are ISDN services and also data rate of PRI is 2.048Mbps while 128-144Kbps. ISDN : Integrated Service Digital Network / It's Some Dumb Network SIP vs BRI/PRI SIP does Best effort Delivery as same as IP traffic do, while BRI/PRI Provide QoS. If someone requires to attain QoS through SIP something like MPLS will do with a considerable amount cost. SIP is more flexible than BRI/PRI because it can be accommodated by company existing data network while BRI/PRI reuires to have a dedicated link for it self.