Stored Program Controlled Network: Prologue

This special issue of The Bell System Technical Journal covers Stored Program Controlled (SPC) network structure and the innovative new service capabilities that this structure makes possible. It follows a series of special issues that have covered individual SPC switching systems and the common-channel interoffice signaling (ccis) system, which is being deployed at a rapid rate to interconnect them. The first step in the evolution of the SPC network was the introduction of No. 1 ESS in Succasunna, New Jersey, in 1965. The principal emphasis in No. 1 ESS design was the use of SPC to replace the earlier wired logic that had been employed in electromechanical switching systems. The use of SPC allowed the introduction of significant new service features, as well as reductions in operating expense. No. 1 ESS was followed by No. 2 ESS and No. 3 ESS, designed to cover suburban and rural segments of the local switching market. Today, more than 2500 local ESSS are in operation, providing nearly 50 percent of Bell System lines with modern circuit switching of voice bandwidth signals. 1575