X.25 is an ISO standard protocol suite that specifies the interface between the DTE and the DCE in a packet-switched network. X.25 defines the lowest three layers of the ISO standard protocol stack model: the physical layer, the link layer, and the network layer. It, like all packet-switching paradigms, was developed to minimize the amount of time it takes for a packet to cross a network link and optimize the use of the available bandwidth of the network.1