The abbreviation of Transmission Control Protocol/Internet Protocol, the Chinese translation is called Transmission Control Protocol/Internet Protocol, also known as Network Communication Protocol. It is the most basic protocol of the Internet and the foundation of the Internet. It consists of the IP protocol of the network layer and the transmission layer. TCP protocol composition. TCP/IP defines how electronic devices connect to the Internet and how data is transferred between them. The protocol uses a 4-layer hierarchical structure, and each layer calls the network provided by its next layer to complete its own needs. In layman's terms: TCP is responsible for discovering transmission problems, sending out signals as soon as there is a problem, requesting retransmission, until all data is safely and correctly transmitted to the destination. And IP is to specify an address for every computer on the Internet.
1. Level overview
In terms of protocol layering model, TCP/IP is composed of four layers: network interface layer, network layer, transport layer, and application layer.
The TCP/IP protocol does not fully comply with the OSI seven-layer reference model. OSI (Open System Interconnect) is a traditional open system interconnection reference model, a 7-layer abstract reference model of a communication protocol, in which each layer performs a specific task. The purpose of this model is to enable various hardware to communicate with each other on the same level. The 7 layers are: physical layer, data link layer, network layer, transport layer, session layer, presentation layer and application layer. The TCP/IP communication protocol uses a 4-layer hierarchical structure, and each layer calls the network provided by its next layer to complete itself. Since the designers of ARPNET pay attention to network interconnection and allow the communication subnet (network interface layer) to adopt existing or future protocols, no special protocol is provided in this layer. In fact, the TCP/IP protocol can be connected to any network through the network interface layer, such as X.25 switching network or IEEE802 local area network.
1) Network interface layer
The physical layer defines various characteristics of the physical medium:
(1) Mechanical characteristics.
(2) Electronic characteristics.
(3) Functional characteristics.
(4) Regulation characteristics.
The data link layer is responsible for receiving IP data packets and sending them through the network, or receiving physical frames from the network, extracting IP datagrams, and handing them to the IP layer.
Common interface layer protocols are: Ethernet 802.3, Token Ring 802.5, X.25, Frame relay, HDLC, PPP ATM, etc.
2) Network layer
It is responsible for the communication between adjacent computers. Its function includes three aspects.
(1) Process the packet sending request from the transport layer. After receiving the request, load the packet into the IP datagram, fill the header, select the path to the sink, and then send the datagram to the appropriate network interface.
(2) Processing the input datagram: first check its legitimacy, and then perform pathfinding--if the datagram has arrived at the sink machine, remove the header and hand over the remaining part to the appropriate transmission protocol; if the datagram has not arrived yet The sink, then forwards the datagram.
(3) Deal with issues such as path, flow control, congestion, etc. The network layer includes: IP (Internet Protocol) protocol, ICMP (Internet Control Message Protocol), control message protocol, ARP (Address ResoluTIon Protocol) address translation protocol, RARP (Reverse ARP) reverse address translation protocol. IP is the core of the network layer. The next hop IP is encapsulated and handed over to the interface layer through routing. IP datagram is a connectionless service.
ICMP is a supplement to the network layer and can send messages back. Used to detect whether the network is unblocked.
The Ping command is to send an ICMP echo packet, and perform a network test through the echo relay sent back.
ARP is a forward address resolution protocol, which uses a known IP to find the MAC address of the corresponding host.
RARP is a reverse address resolution protocol, which determines the IP address through the MAC address. For example, diskless workstations also have DHCP services.
3) Transport layer
provides communication between applications.
Its functions include:
(1) Format the information stream;
(2) Provide reliable transmission. To achieve the latter, the transport layer protocol stipulates that the receiving end must send back an acknowledgment, and if the packet is lost, it must be re-sent.
The transport layer protocols are mainly: Transmission Control Protocol TCP (Transmission Control Protocol) and User Datagram Protocol UDP (User Datagram Protocol).
4) Application layer
provides users with a set of commonly used applications, such as e-mail, file transfer access, remote login, etc. Remote login TELNET uses the TELNET protocol to provide an interface for registration on other hosts on the network. TELNET session provides a character-based virtual terminal. File transfer access FTP uses the FTP protocol to provide file copy functions between machines on the network.
The application layer is generally a user-oriented service. Such as FTP, TELNET, DNS, SMTP, POP3.
FTP (File Transfer Protocol) is a file transfer protocol. Generally, FTP service is used for uploading and downloading. The data port is 20H and the control port is 21H.
Telnet service is a remote login service for users. It uses port 23H and uses clear code transmission, which is poor in confidentiality, simple and convenient.
DNS (Domain Name Service) is a domain name resolution service that provides conversion from domain names to IP addresses.
SMTP (Simple Mail Transfer Protocol) is a simple mail transfer protocol used to control the sending and transfer of letters.
POP3 (Post Office Protocol 3) is the third version of the Post Office Protocol for receiving mail.
The protocols in the network layer mainly include IP, ICMP, IGMP, etc. Because it contains the IP protocol module, it is the core of all TCP/IP protocol-based networks. In the network layer, the IP module performs most of the functions. ICMP and IGMP and other protocols supporting IP help IP complete specific tasks, such as transmission of error control information and control messages between hosts/routers. The network layer is in charge of information transmission between hosts in the network.
The main protocols on the transport layer are TCP and UDP. Just as the network layer controls the data transfer between hosts, the transport layer controls the data that will enter the network layer. The two protocols are the two ways it manages these data: TCP is a connection-based protocol; UDP is a protocol for connectionless service management.
The main shortcomings of the TCP/IP model are as follows: First, the model does not clearly distinguish which are specifications and which are implemented; secondly, the host-network layer of the TCP/IP model defines the interface between the network layer and the data link layer. The difference between the conventional layer and the interface layer is very important, and the TCP/IP model does not distinguish them.
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