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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