Signaling systems and technology

This paper traces the evolution of the signaling art. From early two-state dc signaling arrangements, equivalent to sophisticated doorbell circuits but completely adequate for the early stages of the telecommunications art, to the ultimate of common channel signaling to meet the ever increasing demands of both customer services and communication networks control is discussed. The advantages and disadvantages of the various signaling approaches are reviewed and the differing conclusions reached in the North American Network and the rest of the world are indicated.