A line-side T1 or E1 ISDN-PRI facility is comprised of a group of DS0s. In this context, these DS0s are also called channels. T1 facilities have 23 B-channels and a single D-channel. E1 facilities have 30 B-channels, 1 D-channel, and a framing channel. Data flows bidirectionally across the facility between the server that is running Communication Manager and the ISDN-PRI terminal adapter.