Shulou(Shulou.com)06/01 Report--

First, an overview of the OSI model

OSI (Open System Interconnect Open Systems Interconnection reference Model) is an open systems interconnection reference model jointly developed by the International Standards Organization (ISO) International Telegraph and telephone Advisory Committee (CCITT). It provides a set of standard framework for the network, which is greatly conducive to the development of the network. OSI is divided into seven layers, which are physical layer, data link layer, network layer, transport layer, presentation layer, session layer and application layer.

Second, hierarchical introduction

Physical layer

Function: provide a variety of physical standards

Classification:

Electronic / optical protocols-describe the various characteristics of the signal

Mechanical agreement-specifies the size of the connector or the metal composition of the wire

Functional protocols-describe what to do

Procedural protocols-describe how to do

Features:

① provides data transmission channels for data-side devices.

② transmits data-bit stream

two。 Data link layer

Function: provide layer 2 transmission of data, switch and addressing mode (MAC address)

Typical data link protocols:

IEEE 802.3 / Ethernet protocol

Frame Relay

SONET

ATM (Asynchronous transfer)

Features:

Establishment, dismantling and separation of ① data links

② frame demarcation and frame synchronization-the data transmission unit is a frame

③ controls the sending and receiving sequence of frames

④ error detection and recovery, flow control

3. Network layer

Function: provide three-layer transmission of data, router and addressing mode (IP address)

Mainly responsible for defining packet format and address format, routing data passing through logical network paths

Protocol: IP,ICMP,IGMP,ARP (RARP, proxy ARP, free ARP, reverse ARP)

Features:

① routing and trunking

② sorting, flow control

③ network management

④ service selection

4. Transport layer

Function: to provide reliable or unreliable transmission of data

Agreement:

TCP (Transmission Control Protocol)-provide reliable transmission

UDP (user Datagram Protocol)-unreliable transmission

5. Session layer

Role: provide session management, session establishment, session differentiation, session closure

Separate data from different applications

Case: the process of using a browser

Implementation process:

① maps session addresses to shipping addresses

② data transfer phase

③ connection release

Mode provided: simplex, half duplex, full duplex

6. Presentation layer

Function: provide data presentation standard, data format, data compression, data encryption and other standards

Examples: document format (doc txt pdf...), video format (.avi .rmvb.), compression algorithm, encryption algorithm (MD5...)

7. Application layer

Function: to provide users with software interface

Example: all kinds of software that need to be connected to the network, such as: social software (QQ, Momo.), audio-visual software (QQ Music, Baidu audio-visual...), shopping (Taobao, JD.com.).

Protocol: TELNET,FTP,TFTP,DNS,HTTP,HTTPS,SSH.

three。 Summary

The upper three layers (application layer, presentation layer, session layer) are mainly studied by software engineers.

The lower three layers (transport layer, network layer, data layer) are mainly studied by network engineers.

The lowest layer-the physical layer, is mainly the layer to be studied by communication engineers.

The above is my understanding of the seven-tier OSI model, which is relatively superficial.

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