Wednesday, December 29, 2010

【 Weak current College 】 video-on-demand of unicast, multicast and broadcast 】

Unicast "(Unicast)," multicast "(Multicast) and" broadcasting "(Broadcast) these three terms are used to describe the network communication between nodes. These terms actually mean? difference? .1. unicast: network communication between nodes is like a dialogue between people. If a person is talking to another person, then use network technology terms to describe it is "Unicast", in which case the information received and delivered only between two nodes. Unicast network has been widely used, most of the data on the network is transmitted by unicast, only general Web users do not know. For example, in your email, browse the Web, you must mail server, Web Server establishes a connection, use of the unicast data transfer mode. But usually use a "peer to peer communication" (Point to Point) in place of "Unicast" because "Unicast" General and "multicast" and "broadcast" relative should use. 2. multicast: "multicast" can also be called a "multicast", in network technology and not the many, online video, online video on demand is particularly suited to use multicast mode.   Because if you use unicast mode, the transport, on a per node basis, the number of the destination node, there will be a number of transfer process, which obviously inefficient, it is not desirable if the use does not distinguish between target and send all manner of broadcasting, although one can transfer the data, but obviously cannot distinguish between specific data receiving objects. Using multicast mode, you can achieve a transfer of all the target node of the data, or you can reach only transfer data to a particular object. IP multicast normally through a multicast IP address. Multicast IP addresses are class d IP addresses, i.e. between to Windows 2000 DHCP Manager supports multicast IP addresses automatically assigned. 3. Radio: "broadcast" application in the network, such as client through DHCP to automatically obtain an IP address is achieved by broadcast.But compared with the unicast and multicast, broadcast almost takes the subnet network all bandwidth.   Take a meeting, for example, in the meeting can have only one person speaking, imagine if all the people at the same time to speak with the microphone, the meeting will be messed up.   Hub because it works decided not possible filtering broadcast storm, General switch is not a feature, but now there is network switches (e.g., Omni's QS series switches) also have filtering broadcast storm features, router itself has the function of isolating broadcast storm. Broadcast storm cannot be completely eliminated, but only in the same subnet, as if the speaker's voice can only be transmitted at the same venue, so by hundreds or even thousands of computers in LAN consisting of large and medium-sized, General subnet, as will a Hall with walls isolation into many small offices, in order to achieve the purpose of isolating broadcast storm. In the IP network, broadcast address,, by IP address "," to represent the IP address of the representative of the same subnet as the IP address in all.

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