In a DMR Tier III network the MSO is the part that makes it a network rather than a set of repeaters. Everything about how calls are allocated, who may make them and what happens when a site is lost is decided here.

Logically the MSO comprises a central control unit, a softswitch, a database, network management, a dispatch unit, an MTU and gateways. Physically these can be consolidated or distributed depending on the scale of the network.

• Switching between base stations and between systems
• Subscriber and group management, including dynamic regrouping
• Registration, handover and roaming as radios move across sites
• Control channel reselection when a site's control channel is lost
• Call types — individual, group, emergency, notification, broadcast and all-call
• Data services — short and long text, GPS pull-up, status messaging, emergency alarm
• Priority and rights management, which is what makes emergency pre-emption possible

Local and geographic redundancy, with immediate takeover on failure of the primary equipment. Geographic redundancy means the second copy is not in the same building — which is the only version of redundancy that survives the events it exists for.

SIP interconnection, PSTN and PABX gateways, and interfaces for secondary development. Network, alarm and maintenance management run through the NMC. See DMR Tier III trunking.