Unicast, multicast (multicast) and broadcast differences, engage in communication sorting understand these three things

The three terms unicast, multicast, and broadcast unicast (Unicast), multicast (multicast), and broadcast (broadcast) are terms used to describe how network nodes communicate with each other. So what do these terms mean? What's the difference?

1. Unicast:

Communication between network nodes is like a conversation between people. If a person speaks to another person, the term "unicast" is described in terms of network technology, when the 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 the form of unicast, but the general network users do not know. For example, when you are sending and receiving e-mails, browsing Web pages, you must establish a connection with the mail server, the Web server, and use the unicast data transfer method. However, it is common to use point-to-point communication instead of unicast, because unicast is generally used relative to multicast and broadcast.

2. Multicast:

"Multicast" can also be called "Multicast", the application of network technology is not many, on-line video conferencing, online video-on-demand is particularly suitable for the use of multicast. Because if the unicast mode, node by section, how many target nodes, there will be the number of transmission process, this method is obviously very inefficient, is not desirable, if the use of non-differentiated target, all sent broadcast mode, although the data can be transmitted at one time, but it is clear that the purpose of differentiating the specific data receiving object. 　　By using multicast, the data of all the target nodes can be transferred at once, and the data can only be transferred to specific objects. IP network multicast is generally implemented by multicast IP addresses. The multicast IP address is the class D IP address, which is the IP address between 224.0.0.0 and 239.255.255.255. DHCP Manager in Windows 2000 supports automatic assignment of multicast IP addresses.

3. Broadcast:

"Broadcast" is widely used in the network, such as the process that the client obtains the IP address automatically through the DHCP is realizes through the broadcast. However, compared to unicast and multicast, broadcast consumes almost all the bandwidth of the network within the subnet. Take the meeting for example, there can only be one person speaking at the meeting, imagine if all the people at the same time with the microphone to speak, the venue will be chaos into porridge. Hub because it works to determine the impossibility of filtering the broadcast storm, the general switch does not have this function, but now some network switches (such as the Omni-Direction QS series switch) also has the filtering broadcast storm function, the router itself has the role of isolating broadcast storm. Broadcast storms can not be completely eliminated, but only in the same subnet spread, as if the sound of the horn can only be spread in the same venue, so in the hundreds of or even thousands of computers made up of large and medium-sized LAN, the general sub-network division, like a hall with walls isolated into many small halls, To achieve the purpose of isolating the broadcast storm. In an IP network, the broadcast address is represented by an IP "255.255.255.255", which represents all IP addresses within the same subnet.

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There are three kinds of communication modes in the current network: unicast, broadcast, multicast, which have the advantage of unicast and broadcast at the latest, and have the most development foreground.

1. Unicast:
The host-to-one mode of communication between the hosts, switches and routers in the network are forwarded to the data only and not replicated. If 10 clients require the same data, the server needs to be routed one at a time, repeating the same work 10 times. However, because of its ability to respond to each customer in a timely manner, so now the Web browsing is all using unicast mode, specifically, IP unicast protocol. Routers and switches in the network select the transmission path based on their destination address, transferring the IP unicast data to its specified destination.
Advantages of unicast:
1) The server responds to client requests in a timely manner
2) The server can not send the data to each customer's request, it is easy to realize the personalized service.

The disadvantages of unicast:
1) The server sends data streams for each client, server traffic = number of clients x client traffic, and servers are overwhelmed in streaming media applications where the number of clients is large and each client is heavily traffic.
2) The existing network bandwidth is the pyramid structure, the inter-city inter-provincial backbone bandwidth is only equivalent to all of its user bandwidth of 5%. If you use all unicast protocols, you will be overwhelmed by the network backbone. Current-to-peer applications have often blocked the trunk. It is almost impossible to expand the backbone by 20 times times.

2. Broadcast:
The host a pair of all communication modes, the network to each of the host signals are unconditionally copied and forwarded, all the host can receive all the information (whether you need), because it does not have a path selection, so its network cost can be very low. The cable network is a typical broadcast network, and our TV is actually receiving signals from all channels, but only one channel is restored to the screen. Broadcasting is also allowed in the data network, but it is restricted to the two-layer switch's LAN range, which prohibits broadcast data from passing through the router, preventing broadcast data from affecting large areas of the host.
Advantages of broadcasting:
1) Simple network equipment, simple maintenance, low cost of cloth network
2) Server traffic is extremely low because the server does not send data separately to each client.

Disadvantages of broadcasting:
1) It is not possible to provide personalized service in time for each customer's requirements and times.
2) The network allows the server to provide data with limited bandwidth, the maximum bandwidth of the client = The total bandwidth of the service. For example, the cable client's line support 100 channels (if using digital compression technology, theoretically can provide 500 channels), even if the service provider has more financial resources to allocate more transmission equipment, to the fiber backbone, can not exceed this limit. In other words, it is impossible to provide more diversified and more personalized services to many customers.
3) broadcasts are forbidden to allow transmission over internet broadband Internet.

3. Multicast:
A pair of communication patterns between hosts, that is, a host that joins the same group can accept all the data in the group, and the switches and routers in the network only replicate and forward their required data to the person in need. The host can request to the router to join or exit a group, and routers and switches in the network have the option of replicating and transmitting data, i.e., data is transferred to only those hosts that are in the group. This allows the data to be transferred to multiple hosts that are required (to join the group) at once, and to ensure that other communications from other hosts that do not need to join the group are not affected.
Advantages of multicast:
1) clients that require the same data stream join the same group to share a single data stream, saving the server's load. Have the advantages of broadcasting.
2) Since the multicast Protocol is to replicate and forward the data stream according to the needs of the receiver, the total service bandwidth of the service end is not limited by the bandwidth of the customer's access port. The IP protocol allows for 2亿6千多万个 multicast, so the services it provides can be very rich.
3) This protocol, like the unicast protocol, allows transmission over the Internet broadband Internet.

the disadvantages of multicast:
1) There is no error correction mechanism compared with unicast protocol, it is difficult to make up after packet loss, but it can be compensated by some fault-tolerant mechanism and QoS.
2) Although the current network support multicast transmission, but in the customer authentication, QoS and other aspects need to be perfected, these shortcomings in theory have a mature solution, just need to gradually spread to the existing network.

Unicast, multicast (multicast) and broadcast differences, engage in communication sorting understand these three things