Shulou(Shulou.com)06/02 Report--

Computer network reference model:

Construction: ① layering thought

② OSI reference model

③ TCP/IP protocol family

④ data encapsulation and unencapsulation process

⑤ interlayer communication process

one。 Stratification thought

Let's take the right cases in life as an example:

1. For example, people who enjoy milk may not understand that the production process requires milk from the cow to the tank to collect and transport to the factory, where the raw materials are processed and then packaged and transported to the major shopping malls for retail. Later, we can choose the milk we want according to our different needs.

two。 For example, people who use the network may not understand that the process of data transmission is from a switch through a firewall through the router to the server and then received by the client port.

II. OSI seven-layer reference model

First of all, we need to know what this is:

1. International Organization for Standardization (ISO)

2. The Open Systems Interconnection (OSI) reference model was promulgated in 1984.

3. An open architecture that divides the network into seven layers

Layering and function

Application layer: an interface between network services and end users

Presentation layer: data representation, security, compression

Session layer: establish, manage, and abort sessions

Transport layer: defines the protocol port number over which data is transmitted, as well as flow control and error checking (ports and services are open)

Network layer: logical address addressing to achieve path selection between different networks (need to consider achieving the path at the lowest cost)

Data link layer: establishing logical connection, hardware address addressing (physical), error checking and other functions (arriving at the destination physical node)

Physical layer: establish, maintain, disconnect physical connection

Let's analyze each layer separately for detailed analysis:

Physical layer:

1. How to use physical signals to represent data 1 and 0

two。 Can data transmission be carried out in both directions at the same time?

3. How to establish and terminate a connection between the two sides of the communication

4. Physical interface characteristics

Data Link layer:

1. Data frame encapsulation structure (MAC)

two。 Physical addresses of the source and destination

3. Data check function

Network layer:

1. Packet Encapsulation structure (IP)

two。 Logical address of the source and destination direction

3. Routing according to the logical address of the packet header

Transport layer: (TCP/UDP protocol, directly associated ports)

1. Communication between user processes

two。 form a connecting link between the preceding and the following

Think: what's the difference between end-to-end and point-to-point communication?

Point-to-point: care about how to get there, how to choose the address, address and choose the shortest way (the way to choose the path)

End-to-end: do not care about how to get there or how to select a location, only care about the opening of the service

Session layer:

1. Establish a session relationship between users

Presentation layer:

1. Define the syntax and semantics of conveying information

two。 Encoding and decoding, compression and decompression, encryption and decryption

Application layer:

1. Provide interface with users

3. The composition of TCP / IP protocol family:

1. Application layer: HTTP website (Hypertext transfer Protocol)

FTP (File transfer Protocol) is not fast, has a large capacity, and installs files.

TFTP (simplified File transfer Protocol) has high efficiency and small capacity.

SMTP (Mail transfer Protocol, 25 port)

SNMP (local area network port scanning protocol)

DNS (domain name resolution to IP)

two。 Transport layer: TCP (features: security protocol) such as Thunderbolt and other download tools, breakpoint reconnection

UDP (feature: efficient protocol) Communication tools such as QQ, Wechat and other communication tools will return and resend when the message is not sent successfully.

3. Network layer: ICMP (Datagram Control Protocol) ping tool

IGMP (user Datagram Management Protocol)

IP

ARP (address Resolution Protocol) IP-- > MAC

RARP (inverse address Resolution Protocol) MAC-- > IP

4. Data link layer, physical layer: protocols defined by the underlying network

four。 Data encapsulation process: PDU

Application layer: upper data

Transport layer: TCP header / upper data (data segment)

Network layer: IP header / TCP header / upper layer data (packet)

Data link layer: MAC header / IP header / TCP header / upper data (data frame)

Physical layer: bit stream

five。 Correspondence between devices and layers:

Application layer-computer

Transport layer-firewall

Network layer-Router

Data link layer-switch

Physical layer-network card

To sum up, let me use a life case to illustrate the relationship between the seven layers as a whole, taking a company receiving a project as an example:

Application layer: finally, the most suitable planning plan is submitted to the leader to generate an agreement with Party A.

Presentation layer: the final audit department integrates, reduces and modifies the plan before it is actually submitted, and finally submits it to the general manager

Conversation level: the planning manager integrates the submitted materials, retains the appropriate plans, returns the inappropriate ones, and submits the final copy to the final adjudication department.

Transport layer: due planning manager opens the channel for planning team leaders to submit planning plans.

Network layer: the planning team leader should find out the most concise copy that can express the planning center in this plan, and this copy can attract the upper level to submit it to the planning manager for the purpose of use.

Data link layer: members of the project planning team each collect relevant project information and then conduct a centralized discussion and submit it to the planning team leader

Physical layer: the project department of Party B received a new project and submitted it to the project planning department.

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