In ISDN-PRI, the transmission standard for Layer 1 (the physical layer) is either DS1 T1 or E1. The DS1 T1 (used in North America and Japan) is a digital-transmission standard that carries traffic at the rate of 1.544 Mbps, and the E1 (used in Europe) carries traffic at a rate of 2.048 Mbps. The D (data) channel multiplexes signaling messages for the B (bearer) channels carrying voice or data. In a T1, when a D-channel is present, it occupies Channel 24. In an E1, when a D-channel is present, it occupies channel 16.

Communication Manager offers several administrable protocols, each of which provides a different set of ISDN services. The following combination of services, including but not limited to Basic Call, Basic Supplementary Services, Supplementary Services with Rerouting, Display, and QSIG Networking are supported on the ISDN-PRI interface. Available services outside the United States vary from country to country.

With ISDN, Communication Manager interfaces with a wide range of other products including servers, network switches, and host computers. These products include earlier releases of servers running Communication Manager, public network switches (for example, AT&T 4ESS, Lucent 5ESS, and Northern Telecom DMS250), and other products adhering to the ISDN signaling protocol.

The figure shows an example of how ISDN is used in private and public network configurations. For example, ISDN can be used to connect a switch to a public-switched network, to other switches, and to computers.