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In telecommunication, a primary rate interface (PRI) is an integrated services digital network (ISDN) interface standard (a) that is designated in North America as having a 23B+D channels, (b) in which all circuit-switched B channels operate at 64 kb/s, and (c) in which the D channel also operates at 64 kb/s.
Note: The PRI combination of channels results in a digital signal 1 (T1) interface at the network boundary.
Source: From Federal Standard 1037C
