广播,单播和多播的区别

广播,单播和多播的区别 The difference between broadcast, unicast, and multicast Unicast (Unicast), multicast (Multicast) and broadcast (Broadcast) are three terms used to describe the communication between network nodes. So what exactly do these terms mean? What's the difference? . 1. unicast: communication between network nodes is like a conversation between people. If one speaks to another, then the term "unicast" is described in terms of network technology, where information is received and transmitted only between two nodes. Unicast has been widely used in the network. Most of the data on the network is transmitted in unicast form, but only the general network users do not know it. For example, you must connect with the mail server and the Web server when you send and receive e-mail and browse the web. Unicast data transfer is used at this point. However, Point to Point is often used instead of unicast because unicast is generally used in comparison with multicast and broadcast. 2. multicast: multicast can also be called multicast, and there are not many applications in network technology. Online video conference and VOD are especially suitable for multicast. Because if the unicast transmission node, one by one, the number of the target node, there will be many times the transfer process, which is obviously the efficiency is very low, is not desirable; if the target does not distinguish between, all send broadcast, although a few can be transmitted according to, but obviously not up to identify specific data receiving the purpose of the object. Multicast can not only transfer data of all target nodes at one time, but also achieve the purpose of transmitting data only to specific objects. Multicasting in IP networks is usually achieved by multicast IP addresses. The multicast IP address is the D class IP address, that is, the IP address between 224.0.0.0 and 239.255.255.255. The DHCP manager in Windows 2000 supports the automatic allocation of multicast IP addresses. 3. broadcast: "broadcast" in the network more applications, such as the client through the DHCP automatically obtain IP address is through the broadcast process to achieve. But compared with unicast and multicast, the broadcast takes almost all the bandwidth of the subnet in the subnet. Take a meeting to make an analogy, in the meeting room, only one person to speak, imagine if all the people at the same time with the microphone to speak that meeting will be a mess. The hub because of its working principle decides that it is impossible to filter the broadcast storm, the general switch also have this function, but now some of the network switches (such as omnidirectional QS series switch) also broadcast storm filter function, the router itself has the function of isolating the broadcast storm. The broadcast storm can not be completely eliminated, but can only be spread in the same subnet, like the sound of the horn only under one roof spread like so by hundreds or even thousands of computer composed of large and medium-sized local area network, the general is subnetted, like a large hall with walls separated into many small department of, in order to achieve the purpose of isolating the broadcast storm. In IP networks, broadcast addresses are represented by the IP address "255.255.255.255", This IP address represents all the IP addresses within the same subnet. There are three communication modes in the network: unicast, broadcast, multicast (multicast), the multicast has the latest time, but it has the advantages of unicast and broadcast, and it has the most promising future. Unicast: The "one to one" communication mode between hosts, the switches and routers in the network transmit data only and do not copy. If 10 clients need the same data, the server needs to be sent one by one and repeat the same work 10 times. But because it can respond promptly to each customer, all web browsing now uses IP unicast protocols. Routers and switches in the network select the transmission path based on their destination address and transfer IP unicast data to their designated destination. Unicast advantages: 1. the server responds to the client's request in time 2., the server for each customer does not pass the request to send data, and easy to achieve personalized service. Unicast defects: The 1. server sends data flow to each client, server traffic = client number * client flow; servers are overwhelmed in streaming applications with large customer numbers and large client traffic. 2., the existing network bandwidth is the Pyramid structure, and the inter city backbone bandwidth is only 5% of the total bandwidth of all its users. If all unicast protocols are used, the network backbone is overwhelmed. The current P2P application has made the trunk often blocked, and as long as 5% of the customers are using the network at full speed, the rest of the population will not play. It is almost impossible to expand the trunk 20 times. Two, broadcast: "A mode of communication between the host of all the network without copy and transmit the signal to the conditions of each host are issued, all hosts can receive all the information (whether you need), without the use of path selection, so the network cost can be very low. CATV network is a typical broadcast network, our TV is actually receiving all the channel signal, but only the signal of one channel is reduced to picture. Broadcast is also allowed in data networks, but is restricted to the local area network of the two layer switches, prohibiting broadcast data passing through routers to prevent broadcast data from affecting large areas of hosts. Advantages of broadcasting: 1. network equipment is simple, easy maintenance, low cost network 2. server traffic is very low because the server does not have to send data individually to each client. Disadvantages of broadcasting: 1., unable to provide personalized service for each customer's requirements and time. 2., the network allows the server to provide data with limited bandwidth, and the maximum bandwidth of the client = the total bandwidth of the service. For example, the client cable lines to support the 100 channels (if using digital compression technology, theory can provide 500 channels), even if the service providers have greater financial resources allocation of transmission equipment, more into the optical fiber backbone can not exceed this limit. In other words, it can not provide more diversified and more personalized services to many customers. 3. broadcasting prohibits the transmission on Internet broadband networks. Three multicast: Between the host of "one to one" mode of communication, it is joined with a group of hosts can receive all data from this group, network switches and routers only need to replicate and transmit its data. A host can request, join, or exit a group from a router, and routers and switches in the network selectively copy and transmit data, that is, only the data within the group is transmitted to the hosts that join the group. This allows you to transfer data to multiple hosts that need to be added at once, and to ensure that other communications are not affected by other hosts that do not need to be joined. Multicast advantages: 1., clients that need the same data stream share the same group to share a data stream, saving the server's load. Have the advantages of broadcasting. 2. because the multicast protocol copies and forwards the data stream according to the needs of the receiver, the total bandwidth of the server is not limited by the bandwidth of the client's access terminal. The IP protocol allows 200 million and 6 million (268435456) multicast, so its services can be very rich. 3., this protocol, like unicast protocols, is allowed to be transmitted over Internet broadband networks. Disadvantages of multicast: 1. compared with unicast protocols, there is no error correction mechanism, packet loss is difficult to make up after packet error, but it can be compensated by a certain fault tolerance mechanism and QOS. Although the 2. existing network support multicast transmission, but in client authentication, QOS still need to improve, these shortcomings have a mature solution in theory, just need to be gradually applied to the existing network.