A HELLO message consists information of its neighbors and their link status. The addresses of all the neighbors to which there exists a valid bi-directional links. And addresses of the neighbor that received the HELLO messages. All one-hop nodes receive the message. Every node in the network periodically sends the HELLO messages to its neighbors. As a node receives a HELLO message, it updates its MPR selector table.
The question is how one can select the multi point relay. It is selected independently by each node on the network. The set of MPRs is selected in such a way that all the two hop neighbors are selected, and this information can be retrieved from the HELLO messages received by this node. Only the information of bi directional link nodes is taken. Whenever the node of the network is updated or a node fails, the multipoint relay is recalculated.
The information of MPR should also be mentioned to other nodes. This can be sent with topology control packets. The TC messages sent by the MPR includes its own sequence number to the list. The topology control messages that are sent throughout the network helps in building the topology of the network. The interval of TC messages may depend on the MPR selector set, that if a change occurs then sent early. A node records information about all the multipoint relays, using the information obtained from TC messages. The