In the terminology of the integrated services digital network (ISDN), narrowband refers to bandwidth at the level of DS-1 or less. According to North American standards, a DS-1 translates to an ISDN primary rate interface (PRI), which runs over a T1 facility, which has a signaling rate of 1.544 Mbps.According to European standards, a DS-1 translates to ISDN primary rate access (PRA), which runs over an E-1 facility, which has a signaling rate of 2.048 Mbps. N-ISDN is in contrast to broadband ISDN (B-ISDN), which operates at a rate greater than the primary rate. See also B-ISDN, broadband, DS-1, E-1, ISDN, narrowband, PRA, PRI, signaling rate, and T1.