one . concept
1. computer network ： Is a decentralized , Computer system with independent function （ End system ）, Through communication equipment （ Switch , Router ） And line （ Optical fiber , Cable ） Connect , By fully functional software
System for resource sharing and information transmission .
2. Computer systems are interconnected , Autonomous computer collection ;
interconnection ： Interconnection , communication link
autonomy ： No master-slave relationship
two . function
1. data communication
2. resource sharing ： Hardware , Software , All data can be shared
3. distributed processing ： Multiple computers each undertake different parts of the same task （Hadoop）
4. Improve reliability
5. load balancing
three . form
1. By component ： Hardware , Software , agreement
2. By working mode ：
（1） Edge part ：C/S mode ,P2P mode ; End system
（2） Core part ： Provide services for edge parts . It's a router , Switches or something
3. Divided by functional composition ：
（1） Communication subnet ： Realize data communication
（2） Resource subnet ： Realize data sharing / data processing
Application layer in seven layer model , Presentation layer , The session layer belongs to the resource subnet ; network layer , data link layer , The physical layer belongs to the resource subnet .
four . classification ：
1. By distribution range ：
Wide area network WAN, Metropolitan area network MAN, LAN WAN, Personal local area network PAN
2. By user ：
Public network ： Such as moving , Unicom , Telecom operator
Private network ： troops …
3. By exchange technology ：
Circuit switching , Message exchange , packet switching
4. By topology ：
Bus type , Star type , Ring type , Reticular type
5. By transmission technology ：
（1） Broadcast network ： Shared public communication channel
（2） Point to point network ： Using packet storage and routing mechanism
Technology
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