## 3 Proposed Zone-Based Secure Multicast Techniques
### ZSM Group Management  
The ZSM technique proposed in this paper proposed a group management technique that manages efficiently based zones for multicast member nodes in order to provide strength to the dynamic characteristic of network topology and improve network performance by reducing the amount of control packets. First, nodes participating in the multicast  
Figure 1: Types of nodes in the network.  
calculate their node connectivity, broadcast this information, and then join a zone after receiving information from their neighbors. The group management node is elected within a zone only if there are member nodes in that zone. When a node moves to a new zone and the group member nodes are unknown, the node sends a query to the neighboring nodes of the zone to find the group member nodes. Through this process, the group management node is elected. The group management node maintains information about the member nodes participating in the multicast in the zone and is responsible for issuing member keys to be used in data transmission to each member node. The information about member nodes is stored in the group node table (GNT). The group management nodes must accurately manage the state of the member nodes so that they are not greatly affected by node movement. And the efficiency of data transmission can be increased. Therefore, the GNT is updated by periodically receiving state update information for member nodes. Figure 2 shows the structure of GNT.  
The group management node in each zone broadcasts Hello_GroupManager to inform the overall network. It stores the group management node information existing in the other zone in the neighbor GNT. It periodically broadcasts the GNT management to neighbor group management nodes. When transmitting GNT information, it is encrypted and transmitted to a group key issued from the authentication node in order to prevent data modulation by malicious nodes. Figure 3 shows the pseudo-code for the state information exchange of the group management node.  
If a group management node does not receive state information from a particular member node for a certain period of time, the information on the node is deleted from  
Figure 3: Pseudo code for exchanging status information between group management nodes.  
Figure 2: The structure of group node table.  
GNT. If a member node moves to another zone, it requests that a membership key be issued to the group management node of the moved zone. The group management node receiving issuance of the membership key verifies the node's information in GNT, and the member key is issued if the node's information exists. However, if the information does not exist, it is checked by the group management node of the previous zone, and then the issuance of the member key is decided. If the group management node of the previous zone receives a packet requesting information confirmation, the information of the node is confirmed, and information of the member node is deleted from its GNT. If a member key is issued, its GNT is updated, and the information is transmitted to a neighbor group management node. Through this method, the multicast member nodes are managed, and multicast participation of malicious nodes is prevented through the authentication process for the nodes by using the member key. Figure 4 shows the management method of the member nodes of the group management nodes according to the zone movement of the member nodes.