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Hierarchy, Protocol, Interface, Service
3. Formal awareness of hierarchical structure
The ISO/OSI reference model - how did it come about?
OSI Reference Model vs TCP/IP Reference Model
The OSI reference model is identical to the TCP/IP reference model
Differences between the OSI reference model and the TCP/IP reference model
Hierarchy, Protocol, Interface, Service
1. Why layer?
What to do before sending the file:
(1) The computer that initiates the communication must activate the data communication path.
(2) To tell the network how to identify the destination host.
(3) The computer that initiates the communication should check whether the destination host is powered on and connected to the network normally.
(4) The computer that initiates the communication should find out whether the file management program in the other party's computer is ready for work.
(5) Ensure that errors and accidents can be resolved.
2. How to layer?
Basic principles of layering
1. Each layer is independent of each other, and each layer only implements a relatively independent function.
2. The interface between each layer is natural and clear , easy to understand, and communicate with each other as little as possible.
3. The structure can be separated. Each layer is implemented using the most appropriate technology .
4. Maintain the independence of the lower layer from the upper layer , and the upper layer uses the services provided by the lower layer in one direction .
5. The entire hierarchy should facilitate standardization efforts.
3. Formal awareness of hierarchical structure
1. Entity : The active element in the nth level is called the nth level entity . Entities of the same layer are called peer entities .
2. Protocol : The rules, standards or conventions established for the exchange of data between peer entities in the network are called network protocols. [level]
Syntax: specifies the format of the transmitted data
Semantics: specifies the function to be completed
Synchronization: specifies the sequence of various operations
3. Interface (Access Service Point SAP) : The upper layer uses the entry of the lower layer service.
4. Service : the function call provided by the lower layer for the adjacent upper layer. [vertical]
SDU Service Data Unit: The data that should be transmitted in order to complete the function required by the user.
PCI Protocol Control Information: Information that controls the operation of the protocol.
PDU Protocol Data Unit: A unit of data transferred between peer layers.
4. Summary
Network architecture is a functional description of the computer network structure.
Computer network architecture, referred to as network architecture, is a layered structure .
Each layer follows some/some network protocols to complete the functions of this layer.
Computer network architecture is a collection of layers of computer networks and their protocols .
When the nth layer provides services to the n+1 layer, the service includes not only the functions of the nth layer itself, but also the functions provided by the lower layer services.
There are only interfaces between adjacent layers , and the specific implementation details of the provided services are completely shielded from the upper layer.
Architecture is abstract , while implementation refers to some software and hardware that can run.
reference model
The ISO/OSI reference model - how did it come about?
ISO/OSI Reference Model
1. Application layer
2. Presentation layer
3. Session layer
4. Transport layer
5. Network layer
6. Data link layer
7. Physical layer
OSI Reference Model vs TCP/IP Reference Model
The OSI reference model is identical to the TCP/IP reference model
1. Both are layered
2. Based on the concept of independent protocol stacks
3. Heterogeneous network interconnection can be realized
Differences between the OSI reference model and the TCP/IP reference model
Connection-oriented is divided into three stages. The first is to establish a connection. In this
stage, a request to establish a connection is issued. Only after the connection has been
successfully established, data transfer can begin, which is the second phase.
Then, when the data transfer is complete, the connection must be released. While connectionless-oriented
does not have so many stages, it directly transfers data.
1.0SI defines three points: services, protocols, and interfaces
2.0SI appears first, and the reference model is invented before the protocol, and does not favor a specific protocol
3. At the beginning of the design of TCP/IP, the problem of heterogeneous network interconnection was considered, and IP was regarded as an important layer.
5-layer reference model
