Which layers in the OSI have flow control and what are the differences 25

The role of each layer of the seven-layer model, or the core function, is as follows:

1.Physical layer: completes the transmission of bitstreams between two adjacent nodes.

2.Data Link Layer: Completes the correct transmission of frames between data links. To this end, it is necessary to complete the functions of link management, error control, flow control, etc.

3.Network layer: Complete the correct transmission of end-to-end packets. To this end, it is necessary to complete functions such as routing, error control, and congestion control.

4.Transport layer: Accomplishes the correct transmission of messages end-to-end. To this end, it is necessary to complete the functions of grouping ordering, flow control, error control, and so on.

5.Session layer: The process control that completes the session.

6.Presentation layer: complete the encryption and decryption of messages; compression, decompression; Format conversion between different systems.

7.Application layer: The interface between the system and the user.

The functions of each layer are here, but the network topology is missing.

The data link layer and transport layer provide flow control.

The flow control at the data link layer is oriented to the data frame. The flow control at the transport layer is oriented to packet packets.

In addition, the data link layer can only complete the connection between adjacent nodes, which also restricts its flow control to ensure error-free transmission between adjacent nodes, and the flow control between different nodes may be different in the process of intermediate nodes.

The transport layer implements inter-process communication, and its flow control is based on the communication process. No matter how few nodes pass in between, its flow control is the same.

There are transmission layers and data link layers for flow control.

The transport layer is implemented through a windowing mechanism. When the receiver's cache space begins to be tight, the window value in the trap hall is reduced or even changed to 0 when the acknowledgment packet is sent, which limits the speed at which the sender can send the packet.

The data link layer is responsible for establishing and managing links between nodes. The main function is to turn the error-free physical channel into an error-free data link that can reliably transmit data frames through various control protocols.

The data link layer and the transport layer require flow control, which is controlled by software.

(1) Physical layer.

The unit of data processed by the physical layer is bits, and the physical layer provides a physical link for the data link layer upwards to achieve transparent bit stream transmission services, and the physical layer is connected to the physical layer downwards to determine the mechanical, electrical, functional and process characteristics of the network interface connected to the physical layer.

2) Data link layer.

The data link layer is responsible for transmitting data with frames as PDUs between nodes on a single link, enabling reliable data transmission on less reliable physical links. The main functions of the data link layer include: establishing, maintaining, and releasing data link connections, link access control, flow control, and error control.

3) Network layer.

The PDUs transmitted at the network layer are called packets or packets, which transmit packets between physical networks and are responsible for transmitting packets from the source host to the destination through intermediate nodes. The network layer is the highest layer of the communication subnet, providing both virtual circuit and datagram services to the host. The network layer is mainly responsible for packet ** and route selection, according to the routing table, the packet is transmitted from the origin server to the destination station hop by hop, and can adapt to the change of network load and topology, and dynamically update the routing table.

4) Transport layer.

The transport layer provides end-to-end reliable transmission services between user processes at the source and destination nodes. End-to-end transmission refers to the transmission layer between the two transport layer entities of the source node and the destination node, and does not involve intermediate nodes such as routers. In order to ensure reliable transport services, the transport layer has the following functions:

Network quality of service selection for connection, flow control and congestion control, error control, etc.

5) Session layer.

The session layer adds a mechanism to control the session on the basis of the transport layer service, and establishes, organizes and coordinates the interaction process between application processes. The types of session services provided by the session layer include duplex, half-duplex, and simplex modes. One way of session management is token management, where only the token holder can perform an action.

The session layer provides synchronization control of the session, and when a failure occurs, the session activity is repeated at the synchronization point before the failure point, rather than having to start from scratch.

6) Presentation layer.

The presentation layer defines the format of data exchange between users or applications, and provides conversion services between data representations to ensure that the meaning of the transmitted information remains unchanged after it reaches the destination.

7) Application layer.

The application layer directly faces user applications and provides users with convenient access to various network resources.

Pick up the automatic sense of the encyclopedia.

In the OSI reference model, the protocol layer that implements the end-to-end response, packet sequencing, and traffic control functions is the first layer with traffic control, and the transport layer and data link layer. The transport layer is implemented through a windowing mechanism. When the receiver's cache space starts to run out, the receiver adjusts the value of the window when sending an acknowledgement packet.

Layer 2 Data Link Layer—This is where the data is framed and flow control is handled. This layer.

Specify the topology and provide hardware addressing Layer 4 Transport Layer - General Data Delivery Connection-oriented or connectionless. Include.

Full-duplex or half-duplex, flow control, and error recovery services.

Congestion control still emphasizes the control of physical link traffic! Flow control is mainly a control that emphasizes a theoretical value between the end and the end!

Congestion control is closely related to flow control, but there are also differences: It can be understood in this way that congestion control is the ability of the network to withstand the existing network load and is a global variable; Flow control is often only a local point-to-point control of traffic.

Another important function of the transport layer is flow control, because the flow control of this layer is about the communication host end-to-end.

back, so the flow control of other layers has a clear answer obviously. Introduction to the OSI Reference Model The seven-layer framework of the OSI Reference Model Functions of the Session Layer Provides communication of session processes between different machines.

Flow at the data link layer refers to the flow control between adjacent nodes. The flow control of the transport layer refers to the flow control of the end-to-end transport layer connection.