A coexistence central entity CCE receives deployment messages from each of a plurality of N access nodes. Each deployment message has an identifier of an access node of the plurality and an identifier of a channel in a license-exempt band. From the received deployment messages the CCE compiles and maintains a database which associates each channel with a multicast group. Each multicast group includes all of the access nodes from which was received at least one deployment message identifying a said channel corresponding thereto. When the CCE receives a multicast message from one of the access nodes identifying a given channel, it checks the database to find members of a multicast group associated with the given channel, and notifies at least some of those members of the received multicast message. In this manner the access node's multicast message is forwarded among the whole group.