one , Definition of computer network
1. Definition of computer network ： Computer networks are interconnected , Collection of autonomous computers .
① autonomy ： Interconnected computer systems are independent of each other , There is no relationship between master-slave or control and controlled .
② computer ： Computer equipment .
③ interconnection ： It refers to the use of communication links to link mutually independent computer systems .
2. Currently the largest , The most widely used computer network is the Internet .
3. Packet switching equipment can receive and forward data packets , Is the composition Internet Important foundation of , There are many forms , The most typical are routers and switches .
two , Definition of agreement
1. Definition of agreement ： Protocol is a rule or agreement that needs to be followed in the process of data exchange between network communication entities , It is an important guarantee for the orderly operation of computer network .
2. Three elements of the agreement ： grammar , Semantics and timing
① grammar ： Syntax defines the format and structure of information exchanged between entities , Or set the level of transmission signal between entities, etc .
② semantics ： Define which control information needs to be sent in the information exchanged between entities .
Error detection , Such protocols usually add control information such as error code to the protocol information .
Define what error codes are used for each other , And what kind of error handling mechanism is adopted .
③ sequential ： Also become synchronized , How do entities match or exchange information with each other .
three , Functions of computer network
1. Functions of computer network ： Fast information exchange between different hosts . Through information exchange , Computer network can realize the core function of resource sharing .
2. Resource sharing includes ：
① Hardware resource sharing ： Through computer network , One host can share the hardware resources of another host .
② Software resource sharing ： Hosts on the network can be accessed remotely , Use all kinds of large software running on the server computer .
③ information resources sharing ： The Internet has become an important channel for people to obtain information .
four , Classification of computer networks
The network can be divided into different types according to different classification standards
1. By coverage ：
① Personal area network ： A small-scale network consisting of personal devices through wireless communication technology , Personal devices can be interconnected through Bluetooth . Coverage 1-10m.
② LAN ： Connect the host with high-speed wired or wireless link , Coverage 10m-1km
③ Metropolitan area network ： A city wide network , Coverage 5-50km.
④ Wide area network ： Interconnection of remote man or LAN , It covers tens to thousands of kilometers .
2. Classification by topology
Topology definition coverage diagram advantages and disadvantages
The star topology includes a central node , The host in the network is connected with the central node through point-to-point communication link . The central node is the hub , Switches and other devices are mostly found in local area networks , In a domain network
Easy to monitor and manage , Fault diagnosis and isolation are easy, and the communication range is limited , Fault diagnosis and isolation are difficult , Prone to conflict
The bus topology adopts a broadcast channel as the public transmission medium , Called bus , All nodes are connected to the bus . The communication between nodes is carried out through the shared bus, which is more common in the early LAN
Simple structure , Less cable required , Easy to expand and limited communication range , Fault diagnosis and isolation are difficult , Prone to conflict
Ring topology uses communication links to connect all nodes into a closed ring , The data transmission in the ring is usually one-way transmission , Each node can receive data from the ring , And further forward data to the ring
More common in early LAN , The required cable length in campus network and metropolitan area network is short , Optical fiber can be used , It is easy to avoid conflict. The failure of a node is easy to cause the paralysis of the whole network , The process of adding or withdrawing new nodes is troublesome , There is a waiting time problem .
Mesh topology nodes are directly connected with different nodes through multiple links, which is often seen in wide area networks , High reliability of core network and other networks , When one or more links fail , The network is still connected
Complex network structure , High cost , Routing protocol is complex
Tree topology can be regarded as the expansion of bus or star topology network. At present, many local area networks are easy to expand , Fault isolation is easy and requires high reliability of the root node , Once the root node fails , It may cause the network to be unable to communicate in a wide range .
Hybrid topology is a network composed of more than two simple answer topology networks. Most actual networks are easy to expand , Networks of different sizes can be built , Priority can be given according to demand, and the network structure is complex , Complex management and maintenance
3. Classification by exchange mode
Computer networks can be divided into circuit switched networks , Message switching network and packet switching network
4. Classification by network user attributes
① Public network ： Construction funded by shelves or enterprises , A network that provides paid or free services to the public .
② Private network ： Funded by an organization , It provides network transmission services for the internal business of the organization .
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