Internet TCP/IP system
Source: Shangpin China |
Type: website encyclopedia |
Date: August 24, 2012
Beijing website construction Company Shangpin China: The Internet is a large-scale computer network covering the world, which is connected by multiple networks with different structures through a unified protocol. It is a large-scale Internet that uses routers to realize the interconnection of many WANs and LANs. Users can use the Internet to share resources, exchange information, publish and obtain information around the world. The Internet has played an immeasurable role in promoting the development of science, culture, economy and society in the world.
In October 1995, the Joint Network Committee (FNC) defined the Internet as a global information system. The system has the following three main features:
(1) Computers in the Internet are logically connected together through a global unique address, which is based on the IP protocol or other protocols in the future.
(2) The I'HJ communication of computers in the Internet uses TCP/IP,
(3) The Internet can provide high-level information services for public users or individual users. This service is based on the above communication and related infrastructure.
This definition reveals three characteristics of the Internet: globalization, openness and equality.
TCP/IP system
TCP/IP (Transmission Control Protocol/Internet Protocol) refers to the transmission control protocol/Internet protocol. It originated from ARPANET in the United States. ARPANET began to use the Network Control Protocol (NCP). With the development of ARPANET, more complex protocols are needed. In 1973, ARPANET introduced TCP. Later, it introduced IP in 1981. In 1982, TCP and IP were standardized into TCP/IP protocol family. In 1983, it replaced NCP on ARPANET, and finally formed a relatively complete TCP/IP architecture and protocol specification.
At present TCP/IP is common to all networks and hosts on the Internet for communication Language is also a complete set of standard network connection protocols used on the Internet. Generally speaking, TCP/IP actually contains a large number of protocols and applications, and is composed of multiple independently defined protocols. Therefore, it should be more precisely called TCP/IP protocol family.
TCP/IP was originally used as a standard component in the Berkeley Standard Distribution Center (BSD) UNIX operating system. Therefore, early TCP/II was closely related to the UNIX operating system. With the rapid development and wide application of Internet TCP/IP is not only applied to most computers, from supercomputers to PCs. Major computer and communication manufacturers, including IBM, AT&T, DEC, HP, Sun, etc., provide support for TCP/IP in their products, and various LAN operating systems also incorporate TCP/IP into their own architectures, including Novell Net Ware, Microsoft NT/2000/2003, UNIX, and Linux.
1 . Hierarchy of TCP/IP
The original intention of the OSI reference model research is to provide an international standard for the development of network architecture and protocols. However, due to the rapid development of the Internet in the world, TCP/IP has been widely used. Although TCP/IP is not an ISO standard, its widespread use has also made TCP/IP a "de facto standard" and formed a TCP/IP reference model. However, the development of the OSI reference model also refers to the idea of TCP/IP protocol family and its hierarchical architecture. TCP/IP has also absorbed the concepts and features of OSI standards in the process of continuous development.
TCP/IP has the following characteristics: ① open protocol standard, free to use, and independent of specific computer hardware and operating system; ② Independent of specific network hardware, it can run in LAN and WAN, and is more suitable for the Internet; ③ The unified network address allocation scheme enables the entire TCP/IP device to have a unique address in the network; ④ The standardized high-level protocol can provide a variety of reliable user services.
(1) Network interface layer
The lowest layer of the TCP/IP reference model is the network interface layer, also known as the network access layer. It includes protocols that can communicate with the physical network using TCP/IP, and corresponds to the physical layer and data link layer of the OSI reference model. The TCP/IP standard does not define a specific network interface protocol, but aims to provide flexibility to adapt to various network types, which also shows that the TCP 8 P can run on any network.
(2) Internet layer
The Internet layer is the first layer formally defined in Internet standards. The main function of the Internet layer is to process packets from the transport layer, form packets into packets (IP packets), and select the path for the packets. Finally, the packets are sent from the source host to the destination host. In the Internet layer, the most commonly used protocol is Internet Protocol (IP), and other protocols are used to assist IP operations.
(3) Transport layer
The transport layer of the TCP/IP reference model is also called the host to host layer. Similar to the transport layer of the OSI reference model, it is mainly responsible for end-to-end communication between hosts. This layer uses two protocols to support two data transmission methods, TCP and UDP.
(4) Application layer
In the TCP/IP reference model, the application program interface is the highest level. It has the same tasks as the upper three layers in the OSI reference model, and is used to provide network services, such as file transfer, remote login, domain name service, and simple network management.
2 . TCP/IP protocol
The hierarchy of TCP/IP reference model includes 4 levels, but only 3 levels actually contain the actual protocol. The protocol of each layer in the TCP/IP reference model.
(1) Internet layer protocol
①IP
The task of Internet Protocol (IP) is to address and route data packets and forward them from one network to another. Add a control information before each sent packet, including the IP address of the source host, the address (IP address is equivalent to the logical address of the network layer in the OSI reference model), the IP address of the destination host, and other information. Another task of IP is to split and recompile the data packets that are split at the transport layer. Since data packets are to be forwarded from one network to another, when the size of data packets supported by two networks is different IP needs to divide the data packet at the sending end, and then add control information before each segment for transmission. After the receiver receives the data packet IP reassembles all fragments to form the original data.
IP is a connectionless protocol. No connection means that no end-to-end connection for reliable communication is established between hosts. The source host simply sends IP packets, which may be lost, duplicated, delayed, or in disorder. Therefore, to achieve reliable transmission of data packets, it is necessary to rely on high-level protocols or applications, such as the transport layer's TCPO. IP provides a unified address for the whole network, and addresses are allocated under unified management. The addressing of the Internet layer is realized through this logical address, thus avoiding the difference of physical addresses of different link nodes in the network interface layer.
②ICMP
Internet Control Message Protocol (ICMP) provides error reports for IP. Because IP is connectionless and does not perform error checking, it cannot detect errors when errors occur on the network. ICMP is responsible for reporting errors to the host sending IP packets. For example, if a device cannot forward an IP packet to another network, it sends a message to the source host sending the packet and explains the error through ICMP. Some common error types that ICMP can report are: target unreachable, blocking, echo request, echo response, etc.
③IGMP IP is only responsible for point-to-point packet transmission in the network, while point-to-point packet transmission depends on Internet Group Management Protocol (IGMP). It is mainly responsible for reporting the relationship between host groups so that related devices (routers) can support multicast transmission.
④ ARP and RARP
When the hosts in the computer network want to communicate with each other, they must know each other's physical addresses (the addresses of the data link layer in the OSI reference model). Therefore, in the Internet layer of TCP/IP, there are Address Resolution Protocol (ARP) and Reverse Address Resolution Protocol (RARP), which are used to match the IP addresses of the source host and the destination host with their physical addresses.
(2) Transport Layer Protocol
①TCP
Transmission Control Protocol (TCP) is a connection oriented communication protocol in the transport layer, which can provide reliable data transmission. For the transmission of large amounts of data, reliable transmission is usually required.
TCP divides the data in the application layer of the source host into multiple segments, and then transmits each segment to the Internet layer, which encapsulates the data into IP packets and sends them to the destination host. The Internet layer of the destination host transmits the segments in the IP packet to the transport layer, and then the transport layer reassembles these segments to restore the original data and transmit them to the application layer. In addition TCP also completes the tasks of flow control and error detection to ensure reliable data transmission.
②UDP
User Datagram Protocol (UDP) is a connectionless protocol. It cannot provide reliable data transmission, and UDP does not perform error checking. The application program at the application layer must implement reliability mechanism and error control to ensure the correctness of end-to-end data transmission. Although UDP is very unreliable compared with TCP, it has advantages in some specific environments. For example, if the message to be sent is short, a connection must be established between hosts. In addition, connection oriented communication can only be carried out between two hosts. To achieve one to many or many to many data transmission between multiple hosts. That is, broadcast or multicast, you need to use UDP.
(3) Application layer protocol
In the TCP/IP reference model, the application layer includes all high-level protocols, and new protocols are always added. The application layer protocols mainly include the following:
① Remote Terminal Protocol (Telnet): The local host logs in to the remote host as an emulation terminal to run applications.
② File Transfer Protocol (FTP): to transfer files between hosts.
③ Simple Mail Transfer Protocol (SMTP): realizes the transmission of e-mail between hosts.
④ Domain Name Service (DNS): used to map host names and IP addresses.
⑤ Dynamic Host Configuration Protocol (DHCP): Implement address allocation and configuration of hosts.
⑥ Routing Information Protocol (RIP): used to exchange routing information between network devices.
⑦ Hypertext Transfer Protocol (HTTP): used for data transmission between clients and www servers in the Internet.
⑧ Network file system (NFS): realize the sharing of file systems between hosts.
⑨ Boot Protocol (BOOTP): used to start a diskless host or workstation.
⑩ Simple Network Management Protocol (SNIP): realize network management.
Like the application layer of the OSI reference model, various protocols in the application layer of the TCP/IP reference model are designed and used to provide specific network service functions for network users or applications. This article was published on SEO website optimization Company Shangpin China //ihucc.com/
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