No. 4 Electronic Switching System

The major functional equipment areas include: The processor acts as the CPU for the switch.

A master control console (MCC) provides office technicians access to the switch through the processor peripheral interface (PPI).

[3] It also includes equipment not directly on the PUB including terminating equipment used to connect the switch to the transport network and the TSIs and TMSs, which actually perform the "time-space-time" switching function.

4ESS development began circa 1970, mainly in Naperville, Illinois under the direction of Henry Earle Vaughan.

The decision to switch in a digital voice format was controversial at the time, both from a technical and economic viewpoint.

At the peak of the product's life time in 1999, AT&T employed 145 4ESS switches in its long-haul network, and several were owned by various Regional Bell Operating Companies (RBOCs).

The N4E-N1B includes the 4E APS and 4ESS software, but replaces the 1B processor and the peripheral units which run in emulated environments on an ATCA blade or commercial off-the-shelf servers.

[5] The N4E-N1B is based on the Alcatel-Lucent (now Nokia) gateway platform (7520 Media Gateway (MGW)), 1310 Operations and Management Console – Plus (OMC-P) and the 5400 Linux Control Platform (LCP) and includes other elements such as MRV console terminal servers.