One central objective of DMR is to be repeater transparent. That is, it does not matter which repeater you use. You will always be able to reach the same groups and be always reachable through the same means (private or group call). This concept is violated by the talk groups 8 & 9. The are the regional and local talk groups.
The talk group 9 (TG9) is the so-called local talk group. Group calls to that talk group are not forwarded though the network and only retransmitted locally. Usually “locally” means only the repeater. Sometimes, however, these calls are also forwarded to other repeaters nearby. This case is shown in Example 1.10, “Two regions with two repeaters each.” on the left side. Here DM3MAT sends a group call to TG9 via the repeater DB0ABC. This call is not forwarded to any other repeater and thus is only received in the local area around the repeater. DL1XYZ is in that local area and may receive that call if he configured his radio to receive calls from the TG9.
The talk group 8 (TG8) is the so-called regional talk group. A call to that talk group is usually forwarded to all repeaters within a specific region. Which repeaters are part of a “region”, is a decision of the repeater administrators. So it is hard to predict to which repeaters a regional call gets forwarded. In Example 1.10, “Two regions with two repeaters each.” on the right side, DL3XYZ sends a group call to TG8 to the repeater DB0GHI. This call gets forwarded to all repeaters in the “region”. In this case, also to the repeater DB0JKL within the same region. Therefore, all participants within that region are able to receive the group call if they configured their radios accordingly. In this example, not only DL4XYZ received the call but also DL5XYZ who is not close to the repeater DB0GHI and would have missed a group call to the local talk group.