Structure and functions of layer-7 network protocols

If you want to understand the network protocol, you are not new to the layer-7 network protocol model structure. So here we will explain the specific layer-7 network protocol. First, let's take a look at some definitions of layer-7 network protocol specifications.

OSI Layer-7 network protocol model

The definition and functions of the layer-7 model for Open System Interconnection defined by ISO. it is a stepping stone for network technology creators and a basis for analyzing and judging various network technologies. From now on, the network is no longer mysterious, and it is well-founded and well-founded.

The layer-7 model is mainly used to solve compatibility problems encountered during the interconnection of heterogeneous networks. its biggest advantage is to separate the three concepts of services, interfaces, and Protocols. It also enables different functional modules of the network to share different responsibilities.

An important milestone in network development is ISOInternet Standard Organization (ISO), which defines layer-7 network models for OSIOpen System Interconnect and Open System Interconnection. it not only serves as the basis for judging and analyzing previous and subsequent network technologies, but also serves as a reference model for network protocol design and unification.

The main purpose of establishing a layer-7 model is to solve compatibility problems encountered during the interconnection of heterogeneous networks. its biggest advantage is that it separates the three concepts of services, interfaces, and Protocols: the service shows what functions a layer provides for the previous layer, the interface describes how to use lower-layer services on the previous layer, and how the protocol involves implementing services on the current layer. In this way, each layer is highly independent, there is no limit on the protocols used by each entity in the interconnect network. You only need to provide the same service up and without changing the interfaces of the adjacent layers. the division of layer-7 network protocols also aims to share different responsibilities among different functional modules of the network, which brings the following benefits:

Reduces the complexity of the problem. Once a network fault occurs, you can quickly locate the fault level to facilitate searching and error correction;

Standard interfaces are defined at each layer to enable interoperability between different network devices with the same peer layer. Each layer is relatively independent. A high-level protocol can be run on multiple low-layer protocols; it can effectively stimulate network technology innovation, because each update can be carried out in a small scope, without the need for major network surgery; it is convenient for research and teaching.

Network layering reflects the structured ideas in many engineering designs and is a reasonable division.

Features of layer-7 network protocols

The layer-7 network includes the physical layer, data link layer, network layer, transmission layer, Session Layer, presentation layer, and application layer. the physical layer, data link layer, and network layer are usually called the media layer, which is the object of network engineers. The transport layer, Session Layer, presentation layer, and application layer are called the host layer, it is the content that users are oriented to and interested in.

So what are the specific definitions and responsibilities of layer-7 network protocols?

Level 1-physical layer: the physical layer defines the electrical or mechanical properties of the physical link between communication networks, as well as the operations for activating, maintaining, and disabling this link. physical Layer feature parameters include voltage, data transmission rate, maximum transmission distance, and physical connection media.

Layer 2-data link layer: the actual physical link is unreliable and there will always be errors. The function of the data link layer is to divide the data into frames and transmit the data in data frame units) converts a faulty physical link to a data link that is not faulty at the upper layer. its characteristic parameters include: physical address, network topology, error warning mechanism, sorting of transmitted data frames, and traffic control. the physical address is relative to the network layer address. It represents the node identification technology of the data link layer. The "Topology" is a term frequently encountered in the network, indicates how each device is connected, for example, bus-all devices are connected to a bus, and star-all devices are connected through a central node; an error warning is an error reported during data transmission to the upstream protocol. data frame sorting can re-arrange the transmitted data. traffic control is used to adjust the data transmission rate so that the receiver is not overloaded.

OSL Reference Model

Application Layer

Presentation Layer

Session Layer

Transport Layer

Network Layer

Data Link Layer

Physical Layer

Layer 3-network layer: the network layer divides data into groups of a certain length and identifies the logical addresses of the source and target nodes in the group header. These addresses are like blocks and house numbers, it is the identifier of each node. The core function of the network layer is to obtain the path from the source to the destination based on these addresses. When multiple paths exist, it is also responsible for routing selection.

Layer 4-Transport Layer: provides reliable data transmission that is transparent to the upper layer and does not depend on the specific network. if the network layer is concerned with point-to-point transfer, it can be said that the transport layer is concerned with the final effect of "end-to-end" Source end to the destination end. its functions include flow control, multi-channel technology, virtual circuit management, error correction and recovery. among them, multi-channel technology enables the data of multiple different applications to be transmitted together through a single physical link; virtual circuits are the logical channel for data transmission, which is established, maintained, and terminated at the transmission layer; the error correction function can detect errors and take measures such as retransmission to solve the problem.

Layer 5-Session Layer: establishes, manages, and terminates communication application service requests and responses among network entities.

Layer 6-presentation layer: defines a series of code and code conversion functions to ensure that the source data can be recognized at the destination, such as the ASCII code of the text data that everyone is familiar, indicates the GIF of an image or the MPEG of an animation.

Layer 7-Application Layer: the application layer is the highest level for users. It enables direct conversations between networks and users through software applications, such as finding the target communication party, identifying available resources, and synchronizing operations.

The layer-3 physical layer, data link layer, and network layer of the layer-7 network protocol are usually called media layers. They are not what users see, but silently play a supporting role in the network. They are the objects studied by network engineers; the upper layer transmission layer, Session Layer, presentation layer, and application layer are called the host layer. They are user-oriented and concerned content. These programs often combine the functions of each layer, form a whole in front of the user. all the familiar online applications such as WWW, FTP, and TELNET are integrated with these multi-layer functions.

In actual data transmission, the sender sends the data to the application layer, and adds the control information of the layer to the presentation layer. The presentation layer is processed as a method, and the data is marked with its own ID to the Session Layer. Likewise, each layer adds the control information of the current layer to the received data and sends it to the next layer. When it finally reaches the physical layer, the data is transmitted to the receiver through the actual physical media. the acceptor performs the opposite operation with the sender. from the bottom up, the IDs are removed layer by layer and restored to the original data. it can be seen that the data communication parties must adopt the same protocol in the Peer layer and define the same data identification format, so as to ensure correct data transmission without going through the form.