The D channel carries control and signaling information. The Basic Rate Interface consists of two 64 Kbps B channels and one 16 Kbps D channel. Thus, a Basic Rate user can have up to 128 Kbps service. The Primary Rate consists of 23 B channels and one 64 Kpbs D channel in the United States or 30 B channels and 1 D channel . Integrated Services Digital Network in concept is the integration of both analog or voice data together with digital data over the same network.
Frame relay is an interface used for wide-area networking.
It is used to reduce the cost of connecting remote sites, in any application that would typically use expensive leased circuits. The more locations you have, the greater your savings. With the right carrier service, frame relay network links may be quickly adjusted to meet changes to applications and network topology. Because network managers must react quickly when a new application, organizational unit, business partner or location is needed, leased-line networks often present a roadblock. Using frame relay, backbone changes can be quickly programmed by the carrier, saving the long installation delays and high costs associated with running physical circuits.