CCNA Learning Materials 1.2 OSI Seven-layer Model

By studying this article, you can learn the following:

What is the OSI seven-layer model?The definition and purpose of each layer of OSI. How to use the OSI reference model to analyze the network communication process?

OSI Internet interconnection

The concept of OSI: Open System Interconnect Open System Interconnect reference model, defined by ISO (International Organization for Standardization). It is a flexible, robust and interoperable model.

The purpose of the OSI model is to standardize the interconnection standards of different systems, so that two different systems can communicate easily without changing the logic of the underlying hardware or software.

The OSI model is divided into seven layers:OSI divides the network into seven layers according to levels, from bottom to top, they are the physical layer, the data link layer, the network layer, the transport layer, the session layer, the presentation layer, and the application layer.

Advantages of OSI (not limited to)

The communication process of the network is divided into smaller and simpler components, so it is helpful for the development, design and troubleshooting of each component; through the standardization of network components, it allows multiple suppliers to develop; through the definition in each model What function does the layer implement? Encourage industry standardization; allow various types of network hardware and software to communicate with each other; prevent changes made to one layer from affecting other layers, which is beneficial to development.

OSI reference model

Application layer: various application protocols.

Presentation layer: data formatting, data encryption and decryption, data compression and decompression.

Session layer: establish, manage, and terminate session connections between entities. Transport layer: data segmentation and reorganization; provide end-to-end data services (reliable or unreliable).

Network layer: transfer packets from the source to the destination; logical addressing; routing.

Data link layer: encapsulate packet data into frames; realize communication between two adjacent nodes; error detection.

Physical layer: transmit bits on the medium; provide mechanical and electrical protocols.

OSI Seven-layer ModelFeatures:

  1. Each layer of the OSI model has its own set of functions; 2. The layers are independent and dependent on each other; 3. The upper layer depends on the lower layer, and the lower layer provides services for the upper layer.

Layer 7: Application layer provides interfaces for application software, enabling applications to use network services.

Common application layer protocols: http(80), ftp(20/21), smtp(25), pop3(110), telnet(23), dns(53), etc.

Layer 6: Presentation layer Data decoding and encoding data encryption and decryption data compression and decompression common standards such as: ASCIIJPEG…

Layer 5: The session layer establishes, manages, and terminates the sessions between presentation layer entities, connects to provide sessions between devices or nodes, controls it to coordinate the communication process between systems, and provides 3 different ways to organize the communication between them. simplex, half-duplex and full-duplex

Layer 4: Transport layer Responsible for establishing end-to-end connections to ensure the transmission of messages between end-to-end. Provide reliable and unreliable transmission mechanism. Service point addressing, segmentation and reorganization, connection control, flow control, error control.

Layer 3: Network layer Define logical address, transfer data packets from source to destination

path selection, route discovery, maintenance of routing table

Routing equipment working at the third layer: Router isolates the broadcast domain; isolates the broadcast route selection; maintains routing table addressing and forwarding traffic management connection to the wide area network (WAN)

Layer 2: Data link layer framing, physical addressing, Transfer data frames from one node on the link to another node, flow control, error control, and access control MAC address

Devices working at OSI Layer 2: Switches. Each port is a conflict domain. The entire switch belongs to a broadcast domain.

Layer 1: The physical layer transmits the bit stream on the medium, defines the physical characteristics of the interface and the medium, defines the bit representation, data transmission rate, and signal transmission mode (simplex, half-duplex, full-duplex), and defines the physical topology of the network (network Shape, star, ring, bus, etc.)

Device: Hub, the entire device is in the same collision domain (collision domain) The entire device is in the same broadcast domain (broadcast domain) The device shares bandwidth

Understand the data transmission process with the help of OSI model

Understand the data transmission process (encapsulation process) with the help of OSI model

Understand the data transmission process (decapsulation process) with the help of OSI model

The above is the whole content of the OSI seven-layer model of the CCNA learning materials of SPOTO


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