Computer network architecture
Source: Shangpin China |
Type: website encyclopedia |
Date: August 24, 2012
Computer network is a complex system involving computer technology, communication technology and other fields. Modern computer Beijing website construction The network has penetrated into industry, commerce, government, military and other fields as well as all aspects of people's life. If such a huge and complex system is to operate effectively and reliably, all parts of the network must comply with a set of reasonable and rigorous structural management rules. Computer network is designed according to the highly structured design method and the principle of functional layering, which is also the content of computer network architecture research.
1. Concept of network architecture and protocol
Architecture is a technical science that studies the composition and relationship of various parts of the system. The computer network architecture adopts a layered pairing structure, which defines and describes a set of standards and specifications for the interconnection between computers and their communication facilities. The communication between computer devices can be easily realized by following this set of specifications. The so-called network system is to complete the communication cooperation between computers, divide the functions of each computer connected to each other into clearly defined levels, and specify the protocol of process communication at the same level and the interfaces and services between adjacent layers. These agreements of process communication at the same level and the interfaces of adjacent layers are collectively referred to as the network architecture.
In order to reduce the complexity of the computer network, according to the structural design method, the computer network divides its functions into several layers. The higher layer is based on the lower layer, and provides the necessary service functions for the higher layer. Each layer in the network plays an isolation role, so that changes in the specific implementation methods of lower layer functions will not affect the functions executed by higher layers. The following describes the main concepts involved in network architecture.
(1) Agreement
Protocol is a term used to describe the process of information exchange between processes. In the network, there are many computer systems, and their hardware and software systems are different. To enable them to communicate with each other, there must be a set of communication management mechanism so that both communication parties can correctly receive information and understand the meaning of the information transmitted by each other. In other words, when user applications, file transfer packets, database management systems and e-mail communicate with each other, they must agree on a rule in advance (such as the code, format and how to exchange information). This kind of rule is called protocol. To be precise, protocol is the rule standard or agreement established to realize data exchange in the network.
Network protocol consists of three parts: syntax, semantics and exchange rules, which are the three elements of the protocol: ① syntax determines the format of protocol elements, which specifies the structure and format of data and control information. ② Semantics determine the type of protocol elements, that is, specify what control information to send, what actions to complete, and what responses to make by the communication parties. ③ The exchange rules specify the detailed description of the event realization sequence, that is, to determine the change and process of the communication state, such as the response relationship between the two communication parties.
(2) Entity
In the network hierarchical architecture, each layer is composed of some entities that abstractly represent software elements (such as processes or subprograms) or hardware elements (such as intelligent I/O chips) during communication. Entities are any hardware and software facilities that can send and receive information during communication.
(3) Interface
There should be an interface between adjacent layers in the hierarchy, which defines the original operations and services provided by the lower layer to the higher layer. Adjacent layers exchange information through the interface between them. The upper layer does not need to know how the lower layer is implemented, but only needs to know the services provided by the layer through the interface between layers, so that the two layers maintain functional independence.
For the network structured hierarchical model, its feature is that each layer is based on the previous layer, and the lower layer only provides services for the higher layer. In this way, when each layer implements its own functions, it directly uses the services provided by the lower layer, and indirectly uses the services provided by the lower layer, and provides more perfect services to the higher layer, while shielding the details of specific implementation of these functions.
Hierarchical structure is the basic method to describe the architecture, and the architecture always has the characteristics of layering. The collection of functions, protocols and interfaces of each layer of the computer network defined by the layering research method is called the computer network architecture.
2. Open system interconnection reference model
The realization of communication in computer network must rely on network communication protocol. In the 1970s, the products of major computer manufacturers (such as IBM, DEC, etc.) had their own network communication protocols, which made it difficult for computer systems produced by different manufacturers to be networked. In order to realize data communication between computer systems produced by different manufacturers and between different networks, the International Organization for Standardization (ISO) studied various computer network architectures at that time, and officially published a network architecture model as an international standard in 1984, called the Open System Interconnection Reference Model, That is, OSI/RM (Reference Model of Open System Interconnection/Reference M model), also known as ISO/OSI. "Open" here means that any two OSI/RM compliant systems can be interconnected. When a system can communicate with another system according to OSI/RM, it is called an open system.
The OSI reference model only gives some principled descriptions. It is not a specific network. It divides the functions of the whole network into seven layers, and the communication between two communication entities must follow the seven layer structure, as shown in Figure 5-4. The highest layer of the OSI reference model is the application layer, which provides users with application services; The lowest layer is the physical layer, which connects the communication media to realize data transmission. The connection between layers is made through the interfaces between layers. The upper layer requests services from the lower layer through the interface, and the lower layer provides services to the upper layer through the interface. When two user computers communicate through the network, except for the physical layer, there is no direct communication relationship between the other peer layers. Instead, they communicate through the protocols of each peer layer. For example, the two peer network layers use the network layer protocol to communicate. Only two physical layers can conduct real data communication through media.
In practical applications, when two communication entities communicate through a communication subnet, they must pass through some intermediate nodes. Generally speaking, the nodes in the communication subnet only involve the structure of the lower three layers. Therefore, the hierarchical structure between two communication entities.
The basic functions of each layer of the OSI reference model are as follows:
Layer 1: Physical Layer, which transmits the original data bit stream on the physical channel and provides various transmission media, communication interface characteristics, etc. required for establishing, maintaining and dismantling the physical link connection.
Layer 2: Data Link Layer. On the basis of the physical layer providing bit stream services, it establishes data links between adjacent nodes, provides error free transmission of data frames on the channel through error control, and performs data flow control.
Layer 3: Network Layer, which provides the means to establish, maintain and terminate the network connection for the data transmission of the transmission layer, organizes the data from the upper layer into packets for exchange and transmission between nodes, and is responsible for routing control and congestion control.
Layer 4: Transport Layer, which provides end-to-end (end-user to end-user) transparent and reliable data transmission services for the upper layer. The so-called transparent transmission means that the transmission layer shields the specific details of the communication transmission system from the upper layer during the communication process.
Layer 5: Session Layer, which provides the presentation layer with the functions of establishing, maintaining and ending session connections, and provides session management services.
Layer 6: Presentation Layer, which provides information representation services for the application layer, such as data format transformation, text compression and encryption technology.
Layer 7: Application Layer, which provides various services for network users or applications, such as file transfer, e-mail, distributed database and network management.
From the perspective of the network functions of each layer, the seven layers of the OSI reference model can be divided into: layers 1 and 2 solve the network channel problems; The third and fourth layers solve the transmission service problem; The 5th, 6th, and 7th layers deal with access to application processes.
From the control perspective, the first, second and third layers in the OS1 reference model can be regarded as the transmission control layer, which is responsible for the work of the communication subnet and solving the communication problems in the network; The fifth, sixth and seventh layers are application control layers, which are responsible for the work related to resource subnets and solve the communication problems of application processes; Layer 4 is the interface between communication subnet and resource subnet, which plays the role of connecting transmission and application. This article was published on UEO marketing website construction Company Shangpin China //ihucc.com/
Source Statement: This article is original or edited by Shangpin China's editors. If it needs to be reproduced, please indicate that it is from Shangpin China. The above contents (including pictures and words) are from the Internet. If there is any infringement, please contact us in time (010-60259772).
