Evolution of 5ESS(R) Class 5 Switch to an ISDN PBX

The 5ESS(R) Class 5 Switch is dynamically evolving to meet the needs of the industry and remain state-of-the-art. Its evolution to be part of a private network as an ISDN PBX is described in this paper. The Q.931 protocol (layer 3 of the OSI reference model), supported by the 5ESS Switch, initially supported only the network-side protocol to interface with PBX's. This functionality is being expanded to support the user-side protocol, extending its applications to various ISDN networks.