Division level
When transferring files between two hosts, it is a very complex task.
The work can be divided into three categories:
1. For the transfer file directly, for example, the transmitting end determines the file transfer application should receive end of the file management program is ready to receive and store files. This requires a file transfer module to complete.
2. In order to ensure reliable transfer command files and exchanged between the two systems, you can then set up a communication service module .
3. then construct a network access module , so that the network interface module is responsible for doing detail work related, and provides services to the top, so that the above communication service module to complete the task of reliable communications.
Stratified benefits:
1. Between the layers are independent. How it does not need a layer next level is achieved, but only needs to know the services provided by the interface layer.
2. Good flexibility. When any one is changed, the relationship between the interface layer only needs to remain the same, then this layer above or below the layers are not affected.
3. The structure can be divided into the cut. The layers can be the most appropriate technology.
4. easy to implement and maintain. The system is decomposed into several relatively independent subsystems, easier maintenance.
5. promote standardization. Function of each layer and the services provided have a clear explanation. The main layers are usually to be completed some of the following functions:
1) error control , corresponding to the level of the communication peer is more reliable.
2) flow control , transmission rate of the transmitting end so that the receiving end must be received in time.
3) segmentation and reassembly , data block transmission side to be transmitted is divided into smaller units, the receiving end to restore.
4) Multiplexing and demultiplexing , several high-level session sending a lower layer of the multiplexer is connected, and then demultiplexed at the receiving end.
5) connection establishment and release , before the data exchange to establish a logical connection, the connection is released after the data transfer.
concept
It is a collection of computer network architecture and network protocol layers .
Five agreements
Seven-layer OSI: the application layer, layer, session layer, transport layer, network layer, data link layer, physical layer representation.
TCP / IP architecture: an application layer, transport layer, the IP layer of the Internet, the network interface layer.
Often take advantage of an integrated OSI and TCP / IP in the principles of computer network method uses a protocol that only five of architecture.
Five protocols: the application layer, transport layer, network layer, data link layer, physical layer.
1) Application Layer
The application layer is the architecture of the highest level. Task application layer is done by the interaction between application-specific network applications. Defined application-layer protocol is regular inter-application communication and interaction.
Internet application layer protocol there are many, such as Domain Name System DNS, HTTP protocol support Web applications, e-mail support SMTP protocol. We interact with the application layer data units called packets.
2) Transport Layer
Task transport layer is responsible for providing universal data transmission services in the process of communication between two hosts. With this application process service delivery application layer packets.
The main application layer protocol using two (frequently asked interview):
1. The transmission control protocol the TCP - provide reliable connection-oriented data transmission services, the data transfer unit (85) is a segment .
2. User Datagram Protocol UDP - provides connectionless, best effort to make data transmission services, the unit of data transmission is user datagram.
3) Network Layer
The network layer is responsible for providing communications services to different hosts packet switched network. When transmitting data, the network layer, the transport layer segment or the generated user datagram encapsulated into packets or packets for transmission.
4) Data Link Layer
Referred to as the link layer. When transferring data between two adjacent nodes, the data link layer to the network layer of the IP datagram delivery down assembly into frames transmitted on the link between the two nodes adjacent frames , each frame comprising data and the necessary control information.
5) Physical Layer
The physical layer to consider how much the voltage represents 1 or 0, and the bit reception side recognizes how the transmission by the sender. Also make sure the plug connection cable should have as well as how much root pin pin connections.