Computer Network day05-Layered Models and Protocols
(1) Rules for regulating communications
Agreements are rules agreed upon within a particular group . The communication protocol is the language of communication between the two parties, which is equivalent to the language of human-to-human communication, and is used to transmit messages.
For example, a string of ID numbers:
first 6 digits represent the city-level city where the household registration is located, the middle 8 digits represent the date of birth, the last 3 digits represent the number of people born in the same year, month and day, and the second from the bottom represents the gender, and the odd number is Male, even numbers are female. The last digit is the check code
Protocols are the rules by which anyone communicates with others
In a conversation, people usually do not consider the existence of a protocol unless interrupted, but many actions are important for successful communication. For example, communication can only be successful if two people communicate in a language that both of them can understand.
The protocols by which people communicate (communicate) include separate rules such as meeting, speaking, listening, and understanding. All of these rules are also called communication protocols and represent different levels of communication. Together, these processes help people communicate.
3 different layers of communication
Understand the 3 different layers of communication through conversations between people
Physical layer: both sides of the conversation can express content through sound;,
Rules layer: both parties to the conversation agree to communicate through the same language;
Content layer: The content that both parties of the dialogue need to convey, that is, the content of the communication.
In the process of our communication, we are not aware of the existence of these layers. Of course, these layers are also some things that we abstract. With the help of the concept of layers, we can also divide the complex computer network communication into these abstractions. layers that help us understand how computer networks work.
Computers cannot learn and understand these “network communication protocols” by themselves. All network engineers have written rules that must be strictly followed in order to successfully communicate between hosts.
These rules apply at different layers, such as the physical connection used, how the host listens, how it is translated, and other things.
These rules or protocols that work together to ensure successful communication are grouped into so-called protocol families .
Protocol families and industry standards
In the early days of networking, each manufacturer had their own network equipment and protocols to support the equipment . If a company buys equipment that doesn’t share data with a network other than itself, the network will work just fine. Since companies started doing business with other companies using different network systems, the need for a standard for communication platforms across different network systems has arisen.
Therefore, industry experts and scientists have come together to standardize and standardize network communications by developing a common protocol.
For example, Microsoft, Apple, and Linux operating systems have their own methods of implementing the TCP/IP protocol suite . In this way, users who use the above operating systems can have the same method to connect to the network.
(2) Interaction of protocols
The interaction between a web server and a web browser is an example of a typical application of the protocol suite in network communication. ( Multiple protocols and standards are used for this interaction , and the different protocols work together to ensure that both parties can receive and understand the exchanged data )
The following figure shows the interaction process between the web server and the browser.
The above interaction process uses the following protocols:
Hypertext Transfer Protocol HTTP
HTTP is a common protocol that controls how web servers and web clients interact . HTTP defines the content and format of requests and responses exchanged between clients and servers . Both client software and web server software implement HTTP as part of the application , and the HTTP protocol relies on other protocols to control how data is transferred between the client and server.
Transmission Control Protocol TCP Transmission Control Protocol TCP is a transport protocol used to manage a single session
between a web server and a web client . TCP divides HTTP packets into smaller segments to be sent to the destination client , called data segments. It is also responsible for controlling the size and transmission rate of packets exchanged between the server and the client.
Internet Protocol IP
The most commonly used Internet protocol is the Internet Protocol (IP).
The IP protocol is responsible for obtaining stenciled data segments from TCP , encapsulating them into packets , assigning corresponding addresses , and choosing the best path to the destination host.
Network Access Protocol
Function 1: Describe Data Link Management: The Data Link Management Protocol receives packets from IP and encapsulates them into a format suitable for transmission over the medium.
Function 2: Describe the physical transmission of data on the medium: The standards and protocols of the physical medium specify how signals are sent over the medium and how the receiving client interprets the signals.
The transceiver on the network card (a transceiver is a device for signal conversion) is responsible for implementing the standard used by the medium.
(3) Hierarchical model
The IT industry uses a “layered model” to describe the complex process of network communication. In this process, protocols with different functions are grouped into predefined layers according to their purpose.
Advantages of the layered model :
Define common terms to describe the functions of the network that work across different industries and allow for better understanding and cooperation .
Segmenting the process allows the development of techniques for performing one function independently of techniques for performing other functions . For example, improvements in wireless media technology do not depend on improvements in routers.
Promote competition because products from different manufacturers can be used at the same time.
Provides a common language for describing network functions and capabilities .
Helps with protocol design , because for protocols that work at a particular layer, the way they work and their interface with the upper and lower layers are determined.
(4) Protocol model and reference model
The protocol model provides a model that exactly matches the structure of a specific protocol family. The TCP/IP protocol model describes the functions implemented by each protocol layer in the TCP/IP protocol family. Therefore, it belongs to the protocol model and is a de facto standard.
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