This is the subaddress that, combined with the node's base address, routes an X.25 call to this node's broadcast port without needing a separate routing table entry. This is the addressing mechanism a device or terminal uses to reach the node's broadcast-message function directly, paralleling how cdx6500NMNPCctpSubAddr reaches the control port; both are well-known internal subaddresses baked into the node rather than requiring explicit route configuration. For example, a terminal wanting to send a broadcast message to multiple destinations would dial the node's address plus this broadcast-port subaddress to reach that specific internal function.