Unicast (Unicast: Between main engine “a pair one” the communication pattern, in the network switchboard and the router only carry on the repeater to the data not to make the copy.If 10 clients need the same data, then the server needs to transmit one by one, duplicates 10 time same work.But because its can aim at each customer the prompt response, therefore the present homepage glances over completely all uses the IP unicast agreement.In the network router and the switchboard act according to its goal address selection transmission route, the IP unicast data transfer the destination which assigns to it.
broadcasts (Broadcast: Between main engine “a pair all” the communication pattern, the network the signal which sends out to each main engine all carries on duplicates unconditionally and retransmits, all main engines all may receive all informations (no matter you whether needs, because it does not need the way to choose, therefore its network cost may be very inexpensive.The wired television network is the typical broadcast network, our television in fact is accepts all channels the signal, but only a channel signal reduction picture.Also permits the broadcast in the data network the existence, but it is limited in two switchboard local area network scopes, the prohibition broadcast data traversing router, prevented the broadcast data affects the big area the main engine.
multicast (Multicast: Between main engine “a pair of group” communication pattern, also on joined the identical group's main engine to be possible to accept this group of in all data, in the network switchboard and the router only to has the demand duplication and retransmits its needs the data.The main engine may to the router request joins or withdraws from some group, in the network router and the switchboard has the choice duplication and transmits the data, namely only the data transmission joins the group in for these the group the main engine.Like this both can one time the data transmission for many has the need (to join group the main engine, and can guarantee does not affect other do not need (not to join group the main engine other communications. The
multicast brings the advantage is obvious, but the multicast technology application, very is specially difficult on the Internet multicast application to realize, its reason mainly is the multicast needs the agreement and the equipment support, all is situated between the multicast source (server or multicast proxy server and the receive (client side equipment and so on between router, switchboard, HUB, firewall must support the multicast, but on the Internet network equipment often from the overall efficiency, the security and prevented factors and so on network storm considered, all closes its multicast agreement generally the support, but the link takes office a node not to support to the multicast all can cause the multicast information to be unable the download.Therefore looked on the present network environment, the multicast only can can realize in the terminal local area network or some special nets.

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