DMS switches are divided into four “Functional” areas designed to do certain operations.

These areas are:

• Central Control Complex – Within the Central Control Complex (CCC), the main program in the switch controls the processing of calls, maintenance and administrative routines, and changes the activity for these routines to other areas of the switch.
• Network – The Network Modules (NMs) handle the routing of speech paths between the Peripheral Modules (PMs) and keep these speech connections for the rest of the call.
• Maintenance and Administration – Within the Maintenance and Administration includes Input/Output Controllers (IOCs) – IOCs interface local or remote input/output devices. The I/O devices are used to do testing, maintenance, or administrative functions for the system.
• Peripheral Modules – Peripheral Modules (PMs) are used as interfaces between digital carrier spans (DS-1), analog trunks, and subscriber lines.