Computer Network Overview
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OSI Reference Model
OSI (Open System Interconnect) Open Systems Interconnection i.e., generally called OSI reference model, International Organization for Standardization network interconnection model study in 1985, the structure of the system standard defines seven network interconnection frame (physical layer, data link layer, network layer, transport layer, session layer, presentation layer and application layer), i.e. OSI open systems Interconnection reference model provide further details regarding the function of each layer in this framework, in order to achieve interoperability in an open system environment even, interoperability and application portability, the next will organize a number of knowledge commonly used functions.
| Physical level | Protocol role |
|---|---|
| Application layer | To provide users with services to the user interface |
| Presentation layer | Providing represented as data encryption and compression |
| Session Layer | Determining whether the data to be transferred, establishment and termination of a session management |
| Transport Layer | Reliable and unreliable data transmission, error detection and late |
| Network layer | Logical address addressing, routing implemented between different networks |
| data link layer | Hardware address (MAC) has addressing, error checking |
| Physical Layer | Electrical characteristics for transmission of a bit stream between devices |
The above list is a generic network system model, not a protocol definition. In fact OSI model was never truly over, however, for its wide range of instructional model, network protocols have now been incorporated into the OSI Reference Model within the scope of, OSI reference model, a total of seven layers, each layer has the role described above, which is the basis of knowledge of the networks.
◆ ◆ between each action
Physical Layer: electrical characteristics, the transmission bit stream between devices, transparent transmission bit stream.
Major equipment: repeaters, hubs
Main features: implementing transparent transmission between neighboring nodes bitstream computer, shielded transmission medium specifically as far as possible the physical device, the data link layer above it regardless of what particular network transmission medium is usually in transmitted in the form of binary bits of data.
Meaning: No matter what way transmission of data, equipment used only play the role of a channel, the main role is to be transferred intact spread to other host content.
Expanding knowledge: the transmission distance twisted pair physical layer is 100m, and the signal is attenuated more than 100m, the effect on the transmission of data to the data transmission can be accurately transmitted, relay the transmission signal is amplified, the original data is maintained. accurate, repeater only two Ethernet interfaces.
The data link layer: hardware (MAC) address addressing and error checking, and is responsible for establishing the link between the management node.
Major equipment: network card, bridges, switches (layer switching)
Main features: various control protocols, the physical channel errors become error-free, the transmission data frame is completed can be reliably reliable transmission network between adjacent nodes, by the reliable transmission between the Mac address of the host is responsible for data .
: How the forwarding receiving bit stream data from the physical layer, and encapsulated in a frame transmitted to the same level, but also from the upper hierarchy data frame, disassembly of the bit stream data to the physical layer. and it is also responsible for processing information receiving terminal sends back an acknowledgment frame in order to provide reliable data transmission.
Expanding knowledge: the physical layer bit stream is transmitted, the data transmission link layer is a frame, usually, the layer is generally in turn divided 介质访问控制(MAC)and the 逻辑链路控制(LLC)two sub-layers:
MAC sublayer: The main task is to solve the problem in a multi-user shared networks to channel competition, complete the network media access control.
LLC. Sublayer: The main task is to establish and maintain a network connection, perform error checking, flow control and link control.
Network layer: logical addressing address (IP address), to achieve routing between different networks, is the most complex OSI layer 1, a communication subnetwork 1 is the highest layer.
Major equipment: routers, switches (three-tier exchange)
Mode of operation: By routing algorithm that the router will have routing tables inside, is selected for data transmission between the most appropriate route packets, the forwarding layer control information between the data link layer and the physical layer, to establish, maintain and terminate connected to the network, in general, the data link layer is to solve the unified network communication between nodes, and the network layer is mainly to solve the communication between different subnets.
Advancement of knowledge: the common language data layer addressing, data exchange and selecting an optimum communication path through the routing algorithm, when there are multiple paths between the source node and the routing node, the routing algorithm according to the present layer, through the data network packet selecting the best path, and the most appropriate path from the information, the receiving end of the transmission by the sender.
Transport Layer: achieve reliable two user processes and unreliable data communications between end further having an error detection function.
Major equipment: firewall, intrusion detection system
The main function: to provide reliable, end-user errors and flow control to ensure that the main task of the next three correct transmission of packet data transmission .OSI is the main task of the three-tier data processing, and transport layer the fourth layer, this layer is a sub-network and communication resources and interfaces subnet bridge acts as a connecting link.
Main functions: The transport layer provides transport services between the session layer and network layer, the data obtained from this service session layer, and if necessary, the data is then divided, the transport layer to transmit data to the network layer, and that data. transmitting to the network layer can be accurate, therefore, the transport layer is responsible for providing reliable data transfer between two nodes, two nodes when the link is determined, the transport layer is responsible for overseeing.
The main protocols: the TCP Transmission Control Protocol / UDP User Datagram Protocol port number relates to the use of the service, according to the port number to identify the host service, distinguished session.
Protocol TCP: Transmission Control Protocol, provides a reliable, accurate, connection-oriented protocol.
The UDP protocol: User Datagram Protocol, provides unreliable, connectionless-oriented transport protocol.
UDP and IP transmission similar to the transmission, but the IP protocol is the communication between the ip address, the communication requires a plurality of communication channels, each channel will be assigned to each process used, it is UDP port for communication.
Small Summary: The transport layer effect, one group of packets, to provide a selection of two transport protocol, port package 3, 4 error checking....
Session Layer: is the interface between user applications and the network, primarily for establishing, managing, and terminating sessions.
Main functions: to provide the presentation layer of the two entities and the use of methods to establish the connection, connect the presentation layer between different entities called session, the task of the session layer is to organize and coordinate the communication process between the two sessions, and the exchange of data management.
Presentation Layer: mainly responsible for data format conversion, ie translation, compression and decompression, encryption and decryption.
Main functions: presentation layer is the sixth layer of the OSI model, it commands from the application layer and data interpretation, corresponding to various grammatical meaning given, and according to a certain transmission format to the session layer, whose main function is to process the user that the problem of information, encoding, encryption and decryption of data format conversion, and the like.
Application Layer: The application layer is the highest network system 1 layer, only one layer facing the user, may be viewed as providing a common user interface for the application.
The main protocols: HTTP, HTTPS, the FTP, the SMTP, etc.
Main functions: to provide direct service to the user, complete a variety of work done on the network users want it on the basis of other work on the 6th floor, is responsible for the completion of the link between the application and network operating system, network, establish and end use the link between the person and complete a variety of protocols supervision, management and services and other network services and applications required network by users. in addition, this layer is also responsible for coordination between the various applications.
◆ ◆ OSI model summary
1. The three-tier service to users, the four responsible for actual data transmission.
2. The more intelligent the upper layer, the following layers can identify all of the current data, the closer the user, the more simple the lower layer, the closer the hardware.
3 the next four transmission units:
Transport Layer: The data segment ---> packet
network layer: Packet ---> Packet
data link layer: a data frame
Physical layer: bit
4. The data transmission and reception
Transmitting data from the top down layer transmission
data to an upper layer upon receiving a transmission from the
The cross-layer data can not be transmitted by the interface logic. Between each layer
responsible for the actual data transmission 6. The physical layer, but other layers corresponds to the logic.
7.OSI model is a theoretical model, not corresponding to the actual hardware or protocol.
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TCP / IP reference model
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Common Generic Stack
◆ ◆ TCP protocol
◆ ◆ UDP protocol
◆ ◆ IP protocol
ARP
ICMP
Non peer-peer communication and
Reproduced in: www.cnblogs.com/lyshark