Modern computer network Architecture---Software College of China University of Science and Technology Xiai Computer network is a group of computer systems connected by certain forms, it needs four elements of support, that is, communication lines and communications equipment, with independent functions of the computer, network software support, to achieve data communication and resource sharing. The computer network has two reference models, the OSI model and the TCP/IP model, in which the OSI model is the theoretical model, and the TCP/IP model has become the industry standard of the Internet fact, and now the communication network is generally using the TCP/IP protocol cluster. Application programming is programmed with socket sockets. 1. The network architecture of an important conceptual network structure involves several important concepts. ① protocol: A set of rules, standards, or conventions established for the exchange of data in a computer network. ② Communication protocol: the rules and conventions that both parties must observe together are called communication protocols. The understanding of the data by both parties to the communication needs to be based on conventions and agreements. ③ interface: The boundary between two adjacent layers, which specifies the service provided at the lower level to the upper layer and the formal specification statement (service primitive) used by the service at the interface.
④ Service: A layer provides functionality that can be provided to its adjacent upper layers via an interface. ⑤ Network Architecture: The precise definition of the functions of each layer of computer network and the set of compliance protocols of each layer. ⑥ protocol stack: the protocol sequence in which each layer of the network protocol is arranged in a hierarchical order. ⑦-to-point: physically 22 connections, which are physical topologies, such as fiber, must be point-to-point connections. Dot-to-point protocols are represented in the IP network layer or below two tiers.
The IP network layer is a 22 router for point-to-point communication and does not span other communication devices in the middle. The advantage of point-to-point transmission is that the sending device sends out the data, its task is completed, it does not need to participate in the whole transmission process, so it does not waste the resources of the sending end device. In addition, even if the receiving end device shuts down or fails, the point-to transfer can also be buffered using the storage and forwarding technology. The disadvantage of point-to-point transmission is that after the sender sends out data, it does not know whether the receiving end can receive or receive data. IP and the following layers use point-to-point transmission. ⑧ end-to-end: 22 connections that are logically represented. End-to-end is reflected in the network transport layer, such as to transfer data from A to E, the middle may pass a->b->c->d->e, for the transport layer, it is not aware of the existence of B, C, D, it only think that the message data from a directly to E, which is called end-to-end. In short, end-to-end is made up of countless point-to-point implementations and components. 2. Hierarchical hierarchical model can simplify complex problems, and network layering is based on this principle. Network layering simplifies network design and improves the degree of standardization of network interconnection. Network hierarchy is the last layer is dependent on the next layer, only the bottom is the physical actual communication, the other peer layer is virtual communication. Layering principles and methods as shown, the network layering model involves some of the following terms.
① entities: The active element in each layer can be any hardware or software process that can send or receive information, and in many cases, the entity is a specific software module. ② Peer entity: An entity located in the same layer on different machines. ③ Service provider: N-tier (lower layer) is the service provider for the N+1 layer (upper level).
④ Service User: The N+1 layer (upper level) is an n-tier (lower level) service user. ⑤ Service access Point (SAP): The location provided by the service, which is the exchange of information between adjacent two-tier entities on the interface. ⑥ the relationship between services and agreements: services are vertical, and agreements are horizontal. N-tier service users can only see the N-tier service and cannot see the N-layer protocol, the N-Layer protocol control under the two peer-level communication allows n-tier to provide services to the N+1 layer, to implement N-layer protocol, the need to use the services provided by the N-1 layer.
Graph network layered Model diagram Internet two network models (OSI model and TCP/IP model) are based on the principle of layering. Through the network stratification, can obtain the benefit: Each layer is independent from each other, the adjacent layer interacts only through the interface, causes the entire problem complexity to descend. The structure can be split open, each layer can be used the most appropriate technology to achieve. Each layer features simple, easy to implement and maintain. A layer of changes, as long as the interface service does not change the relationship, the other layer is not affected, the flexibility is good. Stratification facilitates the standardization of network protocols. 3.OSI Network Model
(1) OSI layered Model Open System Interconnection Model (OSI) is a network reference model presented by the International Organization for Standardization (ISO) in 1984. As a conceptual framework, it is proposed that the different device manufacturers and application software developers will follow this standard in the future. Now, this model has become the main model for communication between computers and networks, and most of the network communication protocols currently used are based on the OSI model or the reference OSI model. The OSI model divides the network into seven layers, namely the physical layer, the data link layer, the network layer, the Transport layer, the session layer, the presentation layer, and the application layer, as shown in.
The OSI model is interpreted as follows for each layer of the OSI layered model: The ① physical layer (physical layer) is the lowest level of the reference model. This layer is the data transmission medium of network communication, which is composed of cable and equipment connecting different nodes. The physical layer specifies the mechanical, electrical, functional, and process characteristics that activate, maintain, and close communication endpoints. This layer provides a physical medium for the upper level protocol to transmit data. In this layer, the unit of data is called the bit (bit).
The ② Data link layer is the 2nd layer of the Reference model. The main function is: On the basis of the services provided by the physical layer, the data link connection is established among the entities of the communication, the packets are transferred in "frame", and the error control and flow control methods are used to make the error-prone physical lines become error-free data link.
The ③ Network layer is the 3rd layer of the Reference model. The main functions are: To create a logical link for data transmission between nodes, through routing algorithm to select the most suitable path through the communication subnet, and to implement congestion control, network interconnection and other functions.
The ④ Transport layer (Transport layer) is the 4th layer of the Reference model. The main function is to provide users with reliable end-to-end services that handle packet errors, packet order, and other key transmission issues. The transport layer shields the details of the underlying data communication to the upper layers, so it is a key layer in the architecture of the computer communication.
The ⑤ session layer is the 5th layer of the Reference model. The main function is to maintain the transmission link between the two nodes to ensure uninterrupted point-by-point transmission, as well as to manage data exchange and other functions. The ⑥ presentation layer (Presentation layer) is the 6th layer of the Reference model. The main function is: used to deal with two communication systems to exchange information representation, mainly including data format transformation, data encryption and decryption, data compression and recovery functions. The ⑦ Application layer (application layer) is the highest level of the reference model, providing an interface for operating system or network applications to access network services. (2) The characteristics of OSI model are layered network interconnection model, which is divided into communication subnet and resource sub-network level two structure. Only the physical layers are directly connected, and the same peer protocol is used between peers. When sending data, the data is from the upper level to the lower level, and when the data is received, the data is from low to high.
4. The network layered Data flow description under the picture of the network hierarchy when the streaming diagram. Each layer of the network is treated as a stream, each layer has its own transmission unit, the physical layer transmission unit is the bit stream, and only this layer is the physical data transmission, the other layers are logical; The link Layer transmission unit is the frame; the transmission unit of the network layer is the packet; Transport layer transmission is a segment. The source host application layer data is passed down the layer to increase the corresponding header, called encapsulation, the destination host after the data transfer to the upper layer need to peel off the corresponding header, known as unpacking. Figure Network Layered streaming chart
Modern computer network Architecture
