PRI Reference Points

Depending on country implementation, either the ANSI T1.601 or ITU-T I.431 standard governs the physical layer of the PRI interface.

PRI technology is simpler than BRI. The wiring is not multipoint because there is only the straight connection between the CSU/DSU and the PRI interface. (Multipoint refers to the ability to have multiple ISDN devices connected to the network, all of which have access to the ISDN network.) Arbitration at Layer 1 and Layer 2 allows multiple devices that need to share the ISDN network to access the network without collisions or interruptions. PRI does not require this arbitration because there are no multiple devices.

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