Primary Rate Interface (or PRI) is an ISDN line type.
In Europe, Asia and Australia, the PRI service usually operates on E1 lines up to 2,048 Mbps consisting of 30 64-bit B channels (Bearer) and 64-bit K-64 (64 kBps) D type (Delta) for framing sync.
In the United States and Japan, T1 lines up to 1,544 Mbps are composed of 23 64-bit 64-bit B channels and a 64 kBps D-channel with 8 kBps for framing and synchronization.
It distinguishes itself from the BIS (Basic Rate Interface acronym) that is used when serving fewer channels, as it consists of only two B channels and a D channel at 16 kBps with additional 48 kBps for a total of 192 kBps .
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