The abbreviation of Transmission Control Protocol / Internet Protocol, Chinese translation is called Transmission Control Protocol / Internet Interconnection Protocol, also known as network communication protocol. It is the most basic Internet protocol and the foundation of Internet international Internet network. TCP protocol composition. TCP / IP defines standards for 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 the next layer to fulfill its needs. In layman's terms: TCP is responsible for discovering transmission problems, sending signals as soon as there are problems, requesting retransmissions until all data is safely and correctly transmitted to the destination. IP is to specify an address for each computer on the Internet.
Level overview
In terms of protocol layering model, TCP / IP consists of four layers: network interface layer, network layer, transport layer, and application layer.
The TCP / IP protocol does not fully comply with OSI's seven-layer reference model. OSI (Open System Interconnect) is a traditional open system interconnection reference model. It is 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 at the same level. These 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 its next layer to complete its own network. Because the designers of ARPNET focus on network interconnection, allowing the communication subnet (network interface layer) to use existing or future various protocols, so no special protocol is provided at this level. 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.
Network interface layer
The physical layer defines various characteristics of the physical medium:
1. Mechanical characteristics.
2. Electronic characteristics.
3. Functional characteristics.
4. Characteristics of procedures.
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.
Network layer
Responsible for 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 an 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 find the path-if the datagram has arrived at the sink machine, remove the header and hand over the rest to the appropriate transmission protocol; if the datagram has not yet arrived at the sink , Then forward the datagram.
Third, deal with problems such as path, flow control, congestion and so on. 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, and the next hop IP is encapsulated to the interface layer through routing. IP datagrams are connectionless services.
ICMP is complementary to the network layer and can send messages back. Used to detect whether the network is smooth.
The Ping command is to send an ICMP echo packet and perform a network test through the echo relay.
ARP is a forward address resolution protocol. It 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 by MAC address. For example, diskless workstations also have DHCP services.
Transport layer
Provide communication between applications.
Its functions include: 1. Formatted information flow;
2. Provide reliable transmission. To achieve the latter, the transport layer protocol stipulates that the receiver must send back an acknowledgment, and if the packet is lost, it must be resent.
The transport layer protocols are mainly: Transmission Control Protocol (TCP) and User Datagram Protocol (UDP).
Application layer
Provide users with a set of commonly used applications, such as e-mail, file transfer access, remote login, etc. Telnet Telnet uses the TELNET protocol to provide an interface to register on other hosts on the network. The TELNET session provides character-based virtual terminals. File transfer access FTP uses the FTP protocol to provide a file copy function between machines in 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 for upload and download, the data port is 20H, and the control port is 21H.
Telnet service is a remote login service for users. It uses the 23H port and uses clear code transmission. It has poor confidentiality and is simple and convenient.
DNS (Domain Name Service) is a domain name resolution service that provides conversion between domain names and IP addresses.
SMTP (Simple Mail Transfer Protocol) is a simple mail transfer protocol used to control the sending and transferring of letters.
POP3 (Post Office Protocol 3) is the third version of the Post Office Protocol, used to receive mail.
The protocols in the network layer are mainly 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 functions. ICMP and IGMP and other protocols that support IP help IP accomplish specific tasks, such as transmitting error control information and control messages between hosts / routers. The network layer controls the transmission of information between hosts on 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. Two protocols are the two ways it manages these data: TCP is a connection-based protocol; UDP is a management-oriented protocol for connectionless services.
The main disadvantages of the TCP / IP model are: first, the model does not clearly distinguish which is the specification and which is the implementation; second, the host-network layer of the TCP / IP model defines the interface between the network layer and the data link layer, not The difference between the conventional layer and the interface layer is very important. The TCP / IP model does not distinguish them.
TWO FUNCTION : MCB AND RCCB FUNCTIONS
Residual Current Circuit Breaker With Over Load Protection
Residual Current Circuit Breaker,Residual Current Circuit Breaker with Over Load Protection 1p,Residual Current Circuit Breaker with Over Load Protection 2p
Wenzhou Korlen Electric Appliances Co., Ltd. , https://www.korlenelectric.com