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Modern communications has evolved to a network architecture based on distributed intelligence. First introduced in the public network and later expanded by private network developments, out-of-band signaling has been used to achieve this distributed architecture. Integrated Services Digital Network takes this to the next step by linking private and public networks to each other and to terminals and hosts in a fully distributed processing architecture that allows integrated support of voice, data, and video applications. The next steps in AT&T's ISDN beyond those planned for today will focus on the need to accommodate higher bandwidth and larger capacity and the provision of Universal Information Services.