A resource group usually corresponds to a physical entity such as an adapter or a DSP. Each resource group contains a number of port sets. In a running system, there may be multiple instances of each defined resource group. TDM connection management will create multiple instances of the resource group, depending on how many adapters or DSPs are installed.
The main benefit of the resource group concept is that a resource group is only defined once when a new resource group type is configured, and the actual number of resource groups in the system can be discovered dynamically at system startup. No configuration changes are needed just to add a new instance of an existing resource group.