Frame relay makes sense if your enterprise network interconnects more than four sites and network traffic is fairly heavy. Once attached to the cloud, any site can communicate with any other. Each site has a local connection, which is then connected into a larger packet-switched network. Packet-switched technologies maintain virtual connections between two users. It appears to the end users that they are directly connected, when, in reality, the connection may go through intermediate points.
Virtual connections can either be permanent or temporary.
A permanent virtual circuit is guaranteed to be available at all times. With a temporary, or switched virtual circuit, the connection is set up for the duration of the transmission, then broken down. X.25 is a packet-switched technology that has been used for more than 20 years. It was designed to transport character data from host terminals, and for such low-bandwidth applications, X.25 delivers adequate performance. Frame relay retains many of X.25's good traits, including packet switching, while dropping other traits, such as the overhead.