Private calls allow to call other participants directly without interfering with other calls (except for using the repeater). In the introduction into DMR above, the private call over several repeaters has been described. I consider this aspect of DMR particularly interesting. With the exception of TG 8 & 9, private and group calls are transparent with respect to the repeaters used. It simply does not matter which repeaters are actually used to establish a connection. Therefore, I do not need ot know where the other participants are located.
Consider the typical vacation situation: An OM at his holiday location may want to participate in his local afternoon net. He can do that by simply starting a group call to the nets talk group over the repeater at his holiday location. Now the local holiday repeater has subscribed to the local talk group at home and the OM can participate as usual in the net. The other participants in the net may not even recognize that the OM is at his holiday location.
In a similar fashion, private calls can be started and received at the holiday location. The DMR network knows the repeater a participant was last active on. By briefly pressing the PTT at the holiday repeater, the OM is registered and can now receive private calls at his holiday location. The friends at home may not even know where the OMs current location is nor which repeater to use to reach him. The network takes care of that.
Example 1.11, “Direct calls between countries.” shows such a private call between countries. DM3MAT starts a private call to DL2XYZ using his local repeater DB0ABC. DL2XYZ, however, is at his holiday location in Italy. As he had registered himself at that repeater, the private call gets forwarded to the holiday repeater I0ABC in Italy, where DL2XYZ can receive it. DM3MAT does not need to know the location of the callee nor which repeaters are near to him. This automatic routing of calls (group and private calls) is a major advantage over the analog FM repeater network and EchoLink. For the latter, the ID of the destination repeater needs to be known.