Stored Program Controlled Network: No. 1/1A ESS - SPC Network Capabilitiesand Signaling Architecture

The No. 1 ESS was the Bell System's first major electronic switching system to provide commercial service. It went into service in 1965 and has served since then as a metropolitan local switching system. It uses Stored Program Control (SPC) capabilities to provide basic telephone service, as well as numerous residential and business features. In 1976, an improved metropolitan local switching system, the No. 1A ESS, went into service. It uses the same switching network as the No. 1 ESS, but with a higher performance processor it has about twice the call capacity of No. 1 E S S . Today, No. 1 and No. 1A E S S S serve nearly onehalf of all Bell System subscriber lines. In addition, these systems also provide toll-switching capabilities when they are used as toll offices. In 1976, SPC toll switching systems were first interconnected with a modern common-channel interoffice signaling (ccis) system. No. 1 ESS 1611 joined the resulting SPC network with the introduction of ccis in 1978. No. 1A ESS followed in 1979. The ccis system currently provides toll network signaling improvements, which result in such benefits as faster call setup, as well as trunk and service circuit cost savings. Ultimately, the major benefits to be derived from the use of modern common-channel signaling systems will be in the new features and customer services that they can provide. To fully realize these benefits, the SPC network is being extended to include local switching offices which provide direct interfaces with the customer.