Lucent 5ESS Switch has three main types of modules:

• Switching Module (SM) – Each SM handles several hundred to few thousand telephone lines or several hundred trunks or mixture thereof where each of them has its own processors, also called Module Controllers, which perform most call handling processes, using their own memory boards.
• Administrative Module (AM) – AM is a dual processor mini main frame computer of the AT&T 3B series, running UNIX-RTR. AM contains the hard drives and tape drives used to load and backup the central and peripheral processor software and translations.
• Communication Module (CM) – The Communications Modules form the central time switch of the exchange. 5ESS runs on a Time-Space-Time (TST) topology in which the Time-Slot-Interchangers (TSI) in the Switching Modules (SM) assign each phone call to a time slot for routing through the CM.