Common Channel Interoffice Signaling: 4A Toll Crossbar Application

4A Toll Crossbar Application By K. E. CRAWFORD, C. J. FUNK, P. R. MILLER and J. D. SIPES (Manuscript received May 7, 1977) The No. 4 toll crossbar switching system is presently the backbone of the Direct Distance Dialing (DDD) network. Conversion of No. 4 offices equipped with the Electronic Translator System (ETS) is vital to the rapid introduction of CCIS to the DDD network. CCIS capability represents a major increase in the role of the ETS software in the call switching process. Significant changes and additions to the switching equipment are required to support this expanded software control. I. INTRODUCTION 1.1 General The No. 4 toll switching system comprises a family of common control crossbar switchers which presently form the backbone of the Direct Distance Dialing (DDD) network. 1 As of year end 1976, there were 183 Bell System No. 4 crossbar offices serving this network in the class 1 though class 4 categories, including all ten regional centers and virtually all sectional centers. All but 19 were of the 4A/ETS type which utilizes the Electronic Translator System (ETS) to perform the route translation and network management functions. Although existing No. 4 crossbar offices will be gradually replaced by No. 4 ESS, it is planned to retrofit CCIS into about half of the 4A/ETS offices to expedite the conversion of the DDD network from SF/MF signaling and, therefore, take maximum system advantage of the reduced signaling costs, faster call setup, and new services available with CCIS.