Today, along with the development of network applications, it became more essential to lessen the band width and for this purpose, multi cast service has become more common. One kind of connections in computer networks is multicast in which the destination of sent packages, is a group of receivers. Multicast is a very good network service which delivers data to a group of clients that all are members of a multicast group. This service uses the network band width efficiently and is appropriate specially for multimedia –cast for a group of clients in network. Some of the applications of multicast are video conference, internet television and radio, Elearning and so on. Multicast uses it's own special algorithms to route multicast data. Multicast routing algorithms devide to two general group of tree algorithm: source based tree algorithm and shared tree algorithem. The purpose of multicast routing is to find a tree which includes all routers that have at least one member of group in their subnetworks. Different protocols are designed on the basis of these two routing algorithms among which PIM protocol is used in practical implementation of IP multicast, because of it's advantages. This protocol includes two PIM-DM modes operating on the basis of source based tree algorithm and also PIM-SM on the basis of shared tree algorithm. Although it has advantages, the IP multicast model is not widely implemented. One of the reasons is the non secure IP multicast service. In other words in the 0in 28.3pt 0pt 27pt" dir=ltr Keywords: IP multicast, multicast routing algorithems, access control, authentication, group key.
