One more disadvantage of this scheme will appear if connecting another switch to Switch 1 (see figure). logically, the router will be divided in two parts: the first part deals with unicast packets, the second - with multicast, and for each logical component its own routing table will be formed. The disadvantage of using the multicast is the complexity of network management, since the network should now be viewed in two planes: as unicast and as multicast. Thus, unicast and muticast packets will be distributed on the network simultaneously, i.e. Thus, only one copy of multicast traffic is transmitted to the network segment. A device which perform traffic distribution in multicast networks is called IGMP Querier. Only one IGMP Querier router is enabled in the network segment. Even if there are two routers configured to redirect multicast traffic to one network segment, one of them will be active and the other is set as backup. Step 4a: a client device can opt out of receiving multicast traffic ahead of schedule by sending IGMP Leave message to the Router. Step 4: Router 1 generates IGMP Query messages periodically, checking for active multicast traffic recipients in the network segment. Router 1 will continue the multicast transmission to the segment as long as receives responses to the generated messages. Step 3a: if user starts a program for viewing the surveillance cameras on PC2, then PC2 generates and sends IGMP Membership Report to Router 1. Since PC1 and PC2 are connected to the same Router 1 interface, this interface will not be duplicated in the interfaces list for multicast. Step 3: Router 1 processes the traffic from the multicast source and sends it to the recipients using generated list of interfaces.
Step 2: Router 1, having received the IGMP Membership Report message, adds the interface through which the message was received to the multicast distribution list. Multicast traffic will be transmitted via interfaces from this list. Step 1: user starts a program to view the surveillance cameras on PC1, PC1 generates an IGMP Membership Report message and sends it to Router 1. The group traffic distribution procedure is following: The multicast technology is shown in the figure below. PC1 and PC2 receive video from Camera 1, but, unlike the previous example, traffic is distributed as multicast. Thus, only one copy of the traffic is transmitted between Camera 1 and Switch 1. To perform this the router must be used, which will distribute traffic between sources and destinations. IGMP ( Internet Group Management Protocol) is a network protocol for the interaction of multicast clients and the nearest router. Using IGMP allows to use bandwidth more efficiently. If number of traffic recipients increases, the link load will increase significantly, which will lead to inefficiency of bandwidth using. In the example below PC1 and PC2 receive video from Camera 1 using unicast ( see Figure): PC1 and PC2 establish sessions with Camera 1, and Camera 1 transmits data separately for PC1 and separately for PC2. Thus, two traffic copies are transmitted between Camera 1 and Switch 1. If it is necessary to transmit traffic from one source to several recipients, group transmission mechanism is recommended to use. This data distribution form is called multicast and an example of such a scenario is the video transmission from a surveillance camera to several user devices. Multicast traffic distribution in the network.