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Unicast、Multicast、Broadcast

2022-07-19 03:15:00 【Rock–】

Unicast、Multicast、Broadcast

“ unicast ”（Unicast）、“ multicast ”（Multicast） and “ radio broadcast ”（Broadcast） These three terms are used to describe the communication mode between network nodes . So what exactly do these terms mean ？ Where is the difference? ？ And listen to the following breakdown .

Unicast

The communication between network nodes is similar to the dialogue between people , If one person talks to another , Then the data description using network technology is ”Unicast“ At this time, the acceptance and delivery of messages are only carried out between two points .
(point-to-point) server < ——— ——— > client
Most of the data on the network is transmitted in the form of unicast , It's just that ordinary users don't know . for example , You're on email 、 While browsing the web , Must work with mail server 、Web Server establishes connection , In this case, unicast data transmission mode is used . But usually it uses “ Point to point communication ”（Point to Point） Instead of “ unicast ”, because “ unicast ” Generally speaking, it is related to “ multicast ” and “ radio broadcast ” Use... Correspondingly .

Multicast

“ multicast ” It can also be called “ Multicast ”, There are not many applications of network technology , Online video conference 、 Online video on demand is particularly suitable for multicasting .

Because if you do unicast , Node-by-node transmission , How many target nodes are there , How many times will there be transfers , This approach is obviously highly inefficient , Is not desirable ;

If the target is not distinguished 、 Broadcast mode for all transmissions , Although the data can be transmitted at one time , But obviously, it can not achieve the purpose of distinguishing specific data receiving objects . Adopt multicast mode , The data of all target nodes can be transmitted at once , You can also achieve the goal of passing data only to specific objects .

IP Network multicast is generally through multicast IP Address to achieve . multicast IP The address is D class IP Address , namely 224.0.0.0 to 239.255.255.255 Between IP Address .Windows 2000 Medium DHCP The manager supports multicast IP Automatic address assignment .

Multicast example : client 1 / / / server — — client 2 \ \ \ client 3

Broadcast
“ radio broadcast ”, Can be understood as a person speaking to the whole audience over a loudspeaker , The advantage of this is that the calls are efficient , The message can be transmitted to the whole at once .

“ radio broadcast ” It is widely used in the network , If the client passes DHCP Automatically get IP The process of address is realized by broadcasting . But compared with unicast and multicast , Broadcasting takes up almost all the bandwidth of the network in the subnet . Take a meeting for example , Only one person can speak at the meeting , Imagine if everyone spoke with a microphone at the same time , There will be a mess in the meeting place .

A large number of broadcast packets cannot appear in the network for a long time , Otherwise, the so-called “ Broadcast storm ”. The time taken by broadcast is a large number of data packets , Normal point-to-point communication cannot be carried out normally , The external performance is that the network speed is extremely slow . There are many reasons for the broadcast storm , A faulty network card , It may send broadcast packets to the network for a long time, resulting in broadcast storms .

Broadcast example : ... client 1 client 2 client 3 client 4 ... ---------------------------------------------- \ \ \ | | / / / ---------------------------------------- \ \ \ | | / / / ------------------------------------ \ \ \ | | / / / -------------------------------- \ \ \ | | / / / ------------------------ \ \ \| | / / / server

Because of the working principle of the hub, it is impossible to filter broadcast storms , General switches do not have this function , But now some network switches （ As omnidirectional QS Series switches ） It also has the function of filtering broadcast storms , The router itself has the function of isolating broadcast storms .
Broadcast storms cannot be completely eliminated , But it can only spread in the same subnet , Just like the sound of the horn can only be transmitted in the same field , Therefore, in the large and medium-sized LAN composed of hundreds or even thousands of computers , Generally, subnets are divided , It's like separating a hall into many small halls with walls , In order to isolate the broadcast storm .
stay IP In the network , For broadcast address IP Address “255.255.255.255” To express , This IP The address represents all in the same subnet IP Address .