TCP IP Illustrated

when a multicast datagram is received by a host it

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Unformatted text preview: reception of these multicast frames. This is called "joining a multicast group." (The reason we use the plural "receiving processes" is because there are normally multiple receivers for a given multicast message, either on the same host or on multiple hosts, which is why we're using multicasting in the first place.) When a multicast datagram is received by a host, it must deliver a copy to all the processes that belong to that multicast group. This is different from UDP where a single process receives an incoming unicast UDP datagram. With multicasting it is possible for multiple processes on a given host to belong to the same multicast group. But complications arise when we extend multicasting beyond a single physical network and pass multicast packets through routers. A protocol is needed for multicast routers to know if any hosts on a given physical network belong to a given multicast group. This protocol is called the Internet Group Management Protocol (IGMP) and is the topic of the next chapter. Multicasting on FDDI and Token Ring Networks FDDI networks use the same mapping between the class D IP address and the 48-bit FDDI address [Katz 1990]. Token ring networks normally use a different mapping, because of limitations in most token ring controllers [Pusateri 1993]. 12.5 Summary Broadcasting is sending a packet to all hosts on a network (usually a locally attached network) and multicasting is sending a packet to a set of hosts on a network. Basic to these two concepts is an understanding of the different types of filtering that occur when a received frame passes up a protocol stack. Each layer can discard a received packet for different reasons. There are four types of broadcast addresses: limited, net-directed, subnet-directed, and allsubnets-directed. The most common is subnet-directed. The limited broadcast address is normally seen only when a system is bootstrapping. Problems occur when trying to broadcast through routers, often because the router may not know the subnet mask of the destination network. The results depen...
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This test prep was uploaded on 04/04/2014 for the course ECE EL5373 taught by Professor Guoyang during the Spring '12 term at NYU Poly.

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