While the Primary Rate consists of 23 B channels and one 64 Kbps D channel. Basically ISDN is the integration of both analog and or voice data together with digital data over the same network. Frame relay puts data in a variable-size unit called a frame and leaves any necessary error correction up to the end points, which speeds up overall data transmission. For most services, the network provides a dedicated connection without having to pay for a full-time leased line while the services provider figures out the route for each frame travels to its destination and can charge based on usage. For example an enterprise can select a level of service quality-prioritizing some frames and making others less important.
Frame relay is offered by a lot of service providers.
Frame relay is provided on fractional or full T-1 carriers. Frame relay complements and provides a mid-range service between ISDN and ATM, which operates in a similar fashion to frame relay but at different speeds. Frame relay is often used to connect LANs with major backbones as well as on public WANs and also in private networks with leased lines over T-1 lines. It requires a dedicated connection during the transmission period. Frame relay is not ideally suited for voice or video transmission, which requires a steady flow of transmissions.