2. The so-called simplex communication refers to the working mode that messages can only be transmitted in one direction. For example, remote control and telemetry are simplex communication methods.
Half duplex communication. This way of communication can realize two-way communication, but it can't be done in both directions at the same time, and it must be done alternately. That is, each segment of a communication channel can be a sender or a receiver. But at the same time, information can only be transmitted in one direction. Examples in daily life are walkie-talkie communication, walkie-talkie and so on.
Full duplex communication, also known as two-way simultaneous communication, is an information interaction mode in which both parties can send and receive information at the same time.
3. Topological structure: The topological structure of a computer network refers to the form in which all sites in the network are connected with each other. In LAN, it is obviously the connection form of file server, workstation and cable. At present, the main topological structures are bus topology, star topology, ring topology, tree topology (evolved from bus topology) and their mixtures. As the name implies, the bus type actually connects the file server and the workstation on a common cable called bus, and there must be terminators at both ends of the bus; Star topology takes a device as the central connection point, and all workstations are directly connected to it to form a star; Ring topology is to connect all stations in series to form a ring loop like a chain; It is natural to mix these three basic topologies.
Their respective characteristics:
1, the bus topology is that all devices in the network are directly connected to the public bus through the corresponding hardware interfaces, and the nodes communicate through broadcasting, and the information sent by one node can be "heard" by other nodes on the bus. Advantages: simple structure, easy wiring, high reliability and easy expansion, and it is a common topology structure of LAN. Disadvantages: all data need to be transmitted through the bus, which becomes the bottleneck of the whole network; Fault diagnosis is difficult. The most famous bus topology is Ethernet.
2. Each node of the star topology is connected with the central node through a separate communication line. Advantages: simple structure, easy realization, easy management, easy monitoring and troubleshooting of connection points. Disadvantages: the central node is the reliable bottleneck of the whole network, and the failure of the central node will lead to network paralysis.
3. The nodes of ring topology form a closed loop through communication lines, and the data in the ring can only be transmitted in one direction. Advantages: simple structure, suitable for using optical fiber, long transmission distance and definite transmission delay. Disadvantages: Every node in the ring network becomes the bottleneck of network reliability, and any node failure will cause network paralysis, and fault diagnosis is also difficult. The most famous ring topology network is token ring network.
4. Tree topology is a kind of hierarchical structure, nodes are connected hierarchically, and information exchange is mainly carried out between upper and lower nodes, while data exchange is generally not carried out between adjacent nodes or nodes at the same level. Advantages: simple connection, convenient maintenance, and suitable for the application requirements of collecting information.
5. Mesh topology is also called irregular structure, and the connections between nodes are arbitrary and irregular.
6. A hybrid topology is the simultaneous use of two or more topologies. Advantages: You can learn from each other's strengths in the basic topology of the network. Disadvantages: It is difficult to configure the network and hang the package there.
7. Cellular topology Cellular topology is a common structure in wireless local area networks. It is characterized by point-to-point and point-to-multipoint transmission through wireless transmission media (microwave, satellite, infrared, wireless transmitter, etc.). ). It is a wireless network, suitable for metropolitan area network, campus network, enterprise network, and more suitable for mobile communication. There are other types of topological structures in computer networks, such as the hybrid connection of bus and star, and the hybrid connection of bus and ring. In LAN, star structure is the most widely used.
4. Computer network classification: 1. Classification from network switching function.
Network designers often use data exchange technology according to the network (see 4.2.4). Networks are divided into circuit-switched networks, message-switched networks, packet-switched networks, frame relay networks and ATM (Asynchronous Transfer Mode) networks.
2. Classify from network topology.
Accord to that topological forms of interconnection among network computer, computer networks are divided into star network (the central node of a host is only connected with the host), tree network (multiple computers are connected in layers), bus network (all computers are connected to a trunk line), ring network (all computers form a ring connection), mesh network (any two computers in the network are connected as required) and hybrid network (integration of the above topological structures).
3. Classification from network control mode.
Network managers are often very concerned about network control methods, such as diversity networks, decentralized networks and distributed networks.
4. Classify from the scope of the network.
Networks are divided into three categories according to their geographical scope: local area network, metropolitan area network and wide area network.
WAN usually covers tens of thousands of kilometers, sometimes called long-distance network.
What is the rate of connecting multiple computers through dedicated high-speed communication lines like LAN? The average 10 Mb/s or even 1 000Mb/s is geographically limited to a small area (1 building, 1 unit or 1 several kilometers around).
MAN (also called LAN) has a range of about 5 ~ 100 km between WAN and LAN, and its transmission rate is as high as100 MB/s.
There are other network classification methods, such as dividing private networks and public networks according to the nature of network use; According to the network use scope and environment classification, enterprise network, campus network, etc.; According to the transmission medium, it is divided into coaxial cable network (low speed), twisted pair network (low speed), optical fiber network (high speed), microwave and satellite network (high speed); According to the network bandwidth and transmission capacity, it can be divided into baseband (narrowband) low-speed networks and broadband high-speed networks.
8. Topological structure of satellite communication.
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