Network layering
Baidu Encyclopedia Abstract: Network layering is to send or forward, pack or unpack data to be completed by network nodes, load or unpack control information, etc., which are completed by different hardware and software modules. This can make the complicated problem of communication and network interconnection simpler.
The network layer can be divided into five-layer Internet protocol stack and seven-layer Internet protocol stack
- There are five layers in the Internet protocol stack: application layer, transport layer, network layer, link layer and physical layer.
- The OSI model proposed by ISO divides the network into seven layers, namely the physical layer, data link layer, network layer, transport layer, session layer, presentation layer and application layer.
The following briefly talks about the five-layer Internet protocol
Application Layer
- The application layer provides an interface for user programs to set up communication with another application software.
- The application layer is directly integrated with the application program interface and provides common web application services. The application layer also sends a request to the presentation layer.
- There are many application layer protocols, such as: HTTP, HTTPS, FTP, TELNET, SSH, SMTP, POP3, etc.
- HTTP Hypertext Transfer Protocol is an application layer protocol for distributed, collaborative, and hypermedia information systems. HTTP is the foundation of data communication on the World Wide Web.
- The HTTPS Hypertext Transmission Security Protocol is a transmission protocol for secure communication through computer networks. HTTPS communicates via HTTP, but uses SSL / TLS to add sealed packets. The main purpose of HTTPS development is to provide identity authentication to the website server and protect the privacy and integrity of the exchanged data. This agreement was first proposed by Netscape in 1994 and subsequently extended to the Internet.
- FTP file transfer protocol is an application layer protocol used to transfer files between a client and a server on a computer network. The difference between file transfer and file access is that the former is provided by FTP, and the latter is provided by application systems such as NFS.
- TELNET is an application layer protocol, used in the Internet and regional networks, using the form of a virtual terminal to provide two-way, interactive interaction with the command line interface mainly based on text strings. One of the TCP / IP protocol families is the standard protocol and main method of remote login service on the Internet. It is often used for remote control of the server and allows users to perform work on the remote host from the local host.
Transport Layer
- The transport layer adds the transmission header (TH) to the data to form a data packet. The transmission header contains the transmission information such as the protocol used. Provide users with reliable end-to-end (End to End) services.
- The transport layer is responsible for providing data transmission services between application processes for the source and sink. This layer mainly defines two transmission protocols, the transmission control protocol is TCP and the user datagram protocol UDP.
- The transport layer only cares about the start and destination of the communication, and does not care about the secondary technical process of the data packet.
- Protocols with transport layer functions: TCP, UDP, SPX, etc.
- TCP / IP is the most famous transmission control protocol, and its name is borrowed from the name of the entire suite. It is used for connection-oriented transmission, and the connectionless user datagram protocol UDP is used for simple message transmission.
Network Layer
- The network layer provides routing and addressing functions, enabling two terminal systems to interconnect and determine the best path, and has certain congestion control and flow control capabilities. This is equivalent to needing an address when sending mail. Because the network layer function in the TCP / IP protocol system is specified and implemented by the IP protocol, it is also called the IP layer.
- The network layer is responsible for sending datagrams independently from the source to the sink, and mainly solves the problems of routing, congestion control and network interconnection. That is to create a logical link for data transmission between nodes (routing and forwarding of data packets).
- Network layer protocols: IP, ICMP, IGMP, IPsec, etc.
- IP Protocol Internet Protocol / Internet Protocol, a network protocol used to encapsulate and exchange data, decide how to deliver information based on the destination IP address of the data packet.
- The IP protocol is the main protocol of the network layer in the TCP / IP protocol family. The task is only to transfer data according to the addresses of the source host and the destination host. For this purpose, IP defines the addressing method and the encapsulation structure of the datagram. The main version of the first architecture is IPv4, which is still a widely used Internet protocol, although IPv6 is being actively deployed around the world.
- Equipment with network layer functions: routers, layer 3 switches, etc.
Data Link Layer
- The data link layer is located between the physical layer and the network layer. In broadcast multiple access links (LAN), due to possible media contention, it can also be subdivided into media access control (MAC) sublayer and logical link control (LLC) sublayer, media access control (MAC ) The sub-layer is dedicated to deal with the contention and conflict of media access.
- The data link layer is responsible for encapsulating the IP datagram into a frame format suitable for transmission on the physical network and transmitting it, or decapsulating the frame received from the physical network, and taking out the IP datagram to the network layer. That is to provide establishment, maintenance and release management of data link connection between two network entities.
- Data link layer protocol: asynchronous transmission mode, VLAN, PPP, Ethernet, Wi-Fi, etc.
- Common data link layer devices: network cards, switches, bridges, etc.
Physical Layer
- The physical layer is the physical layer of the network to ensure that the original data can be transmitted on various physical media.
- Provide the data transmission path for the data terminal equipment, responsible for transmitting the bit stream between the nodes, that is, responsible for the physical transmission. The protocol of this layer is related to both the link and the transmission medium. Define how physical devices transmit data;
- Physical layer protocol: IRDA physical layer, USB physical layer, telephone network, etc .;
- Common physical layer equipment: optical fiber, hub, serial port, parallel port, etc .;
