Đang tải... (xem toàn văn)
Giới thiệu về multicast groups .các giao thức chạy trong định tuyến multicast
Multicast networking Multicast Broadcast Class MulticastSocket Using multicast A peer-to-peer multicast chat system A client/server multicast chat system Wrapping up Conclusion Multicast networking Multicast and broadcast are datagram network protocols. Broadcast packets can not get across a router, while multicast packets can. Multicast, thus, requires a router to be multicast aware: both the hosts and routers must support IGMP. Multicast networking Internet Group Management Protocol (IGMP) Hosts willing to receive multicast messages (packets) need to inform their immediately- neighboring routers that they are interested in receiving multicast messages sent to certain multicast groups. This way, each node can become a member of one or more multicast groups and receive the multicast packets sent to those groups. The protocol through which hosts communicate this information with their local routers is called Internet Group Management Protocol (IGMP). Multicast A packet is sent to a multicast group. All the interested recipients in the group will receive the packet. As with UDP, multicast is packet-based and does not guarantee reliability. Successful delivery may be different for different recipients in packet lost, duplication, and order. Multicast groups A multicast group is simply an IP address that falls into IP class D (224.0.0.0~239.255.255.255). Recipients express an interest in receiving packets addressed to a particular multicast group. The underlying network protocols announcing this interest to relevant routers on the network. Multicast groups To multicast is to simply insert a packet into the network with the appropriate target address. A sender need not even be a member of the group. The packet will also be picked up by routers that will forward it as appropriate to adjacent networks that are interested. The significant complexity of multicast is how routers will know what adjacent networks are interested. Multicast groups The MBone The largest deployment of multicast on the Internet is perhaps the Mbone. A multicast packet is transported as usual within a island, but is also picked up by router hosts that transmit the data through TCP tunnels to other router hosts on other islands. TTL-Time To Live Multicast packets use a TTL field to limit how far a packet will propagated. The definition of the TTL field depends on the routing protocol. Reliability There are other reliable multicast protocols such as MTP, RAMP, RMP, RMTP, RTP, TMTP, or XTP. [...]... to receiving multicast packets from a single host, from which they came from They are usually not allowed to transmit multicast packets IGMP must be used Using multicast Using multicast is similar to using UDP except that a TTL can be specified when a packet is sent through a MulticastSocket Using multicast Receiving a multicast packet involves one more step The receiver must join a multicast group... port on a single machine, while many clients can engage in the same multicast conversation from a single machine Class MulticastSocket The MulticastSocket class extents the DatagramSocket class by adding support for IP multicast The additional methods are: Methods to control group membership A send() method that allows the TTL of a multicast packet to be specified Java does not support querying the...Broadcast Similar at a local level to multicast: every broadcast-based network has a broadcast address Clients must choose a UDP port number on which to operate Multicast vs broadcast Multicast is preferable Multicast is often supported correctly, but broadcast results in a permission error Multicast and broadcast result in almost the same traffic From java, only... packets to arrive An code frag ment A peer-to-peer multicast chat system Multicast and broadcast allow the development of true peer-to-peer applications - there is no central server This example shows how clients in a multicast- based chat system communicate among each other A client/server multicast chat system This implementation combines unicast and multicast to overcome the Java applet security limitation... client unicasts its message to a central server, which then multicast it back to all the client This requires that the server must reside at the Web server’s location to comply with Java applet security limitation A client/server multicast chat system This system consists of two classes – MixedcastChat and MixedcastServer A client/server multicast chat system To deployed as a web-based chat system,... MixedcastChat and MixedcastServer A client/server multicast chat system To deployed as a web-based chat system, the server must run on the same machine as the web server Client can only connect if they are multicastconnected to the server . Multicast networking Multicast Broadcast Class MulticastSocket Using multicast A peer-to-peer multicast chat system A client/server multicast chat system Wrapping up Conclusion Multicast. receiving multicast messages sent to certain multicast groups. This way, each node can become a member of one or more multicast groups and receive the multicast packets sent to those groups. . complexity of multicast is how routers will know what adjacent networks are interested. Multicast groups The MBone The largest deployment of multicast on the Internet is perhaps the Mbone. A multicast