What are the commonly used network protocols?
Network protocols are a collection of rules, standards, or conventions established for the exchange of data in a computer network. Network protocols are essentially rules, i.e., common codes that various hardware and software must follow. Network protocols are not a separate set of software; they are integrated into all other software systems, so it can be said that the protocols are ubiquitous in the network. Network protocols span all levels of the OSI communication model, from the very familiar TCP/IP, HTTP, and FTP protocols to protocols such as OSPF and IGP, of which there are thousands.
The common network protocols are as follows:
TCP/IP protocol, IPX/SPX protocol, NetBEUI protocol
TCP/IP is the abbreviation of “transmissionControlProtocol/InternetProtocol TCP/IP is the abbreviation of “transmissionControlProtocol/InternetProtocol”, the Chinese translation for the transmission control protocol/Internet protocol) protocol, TCP/IP (Transmission Control Protocol/InterNet Protocol) is a network communication protocol, which regulates all communication devices on the network, especially between a host and another host of the data traffic format and transmission methods. TCP/IP is the foundation of INTERNET and a standardized method for packaging and addressing computer data. In data transmission, can be visualized as having two envelopes, TCP and IP are like envelopes, the information to be transmitted is divided into a number of segments, each segment is stuffed into a TCP envelope, and on the face of the envelope to record the segment number of information, and then the TCP envelope is stuffed into a large IP envelope, sent to the Internet. On the receiving end, a TCP package collects the envelopes, pulls out the data, restores them in the order in which they were sent, and checks them, and if an error is found, TCP will ask for a resend. Therefore, TCP/IP can transmit data almost error-free in the INTERNET. For the average user, it is not necessary to understand the entire structure of the network protocol, only need to understand the IP address format, you can communicate with the rest of the world network.
IPX/SPX is based on Xerox’s XEROX’SNetworkSystem (XNS) protocol, and SPX is based on Xerox’s XEROX’SSPP (SequencedPacketProtocol) protocol, both of which were developed by novell. They are both high-speed protocols developed by novell for use in LANs. A significant difference between it and TCP/IP is that it does not use ip addresses, but rather the physical address of the network card, i.e., the (MAC) address. In practice, it basically does not require any setup and can be used as soon as it is installed. Because it played a huge role in the early days of network popularization, it was supported by many vendors, including microsoft, and now many software and hardware also support this protocol.
NetBEUI is NetBiosEnhancedUserInterface, or NetBios Enhanced User Interface. It is an enhanced version of the NetBIOS protocol, which has been adopted by many operating systems, such as WindowsforWorkgroup, Win9x series, Windows NT, etc. The NETBEUI protocol is useful in many situations, and is the default protocol for operating systems prior to WINDOWS98. In short, NetBEUI protocol is a short, compact and efficient broadcast protocol that does not need to be set up after installation, and is especially suitable for transmitting data in the “Network Neighborhood”. Therefore, it is recommended that in addition to TCP/IP protocol, LAN computers should also install NetBEUI protocol. In addition, there is a point to note that if a WINDOWS98 machine with only TCP/IP protocol is to be added to the WINNT domain, NetBEUI protocol must also be installed.
Telnet (RemoteLogin): Provides a remote login function that allows a computer user to log on to another computer remotely, as if operating directly from the remote host.
FTP (FileTransferProtocol): a remote file transfer protocol that allows users to copy files from a remote host to their own computer.
SMTP (SimpleMailtransferProtocol): Simple Mail Transfer Protocol, used to transfer e-mail.
NFS (NetworkFileServer): a network file server that allows multiple computers to transparently access each other’s directories.
UDP (UserDatagramProtocol): User Datagram Protocol, which is located in the transport layer like TCP and is used in conjunction with the IP protocol to omit the packet header when transmitting data; however, it does not provide for retransmission of packets, so it is suitable for transmitting shorter files.
The rest are DNSFTPTELNETSMTPPOP3 and so on.
Network protocols are made up of three elements:
Semantics: semantics is the interpretation of the meaning of each part of a control message. It specifies what kind of control message needs to be sent, as well as the actions to be accomplished and what kind of response to make.
Syntax: Syntax is the structure and format of user data and control messages, and the order in which the data appears.
Timing: Timing is a detailed description of the order in which events occur. (It can also be referred to as “synchronization”).
These three elements have been imaginatively described as: semantics for what is to be done, syntax for how it is to be done, and timing for the order in which it is to be done.
What is ftp
ftp means File Transfer Protocol.
FTP (FileTransferProtocol) is a set of standard protocols used to transfer files over a network, and it belongs to the application layer of network transfer protocols. Its primary function is to transfer files between a server and a client. This protocol uses clear text transfer.
FTP server functions in addition to simple file transfer and management, based on the configuration of the server software architecture, it can also provide the following main functions:
1, different users: FTP server in the default situation, based on the user login is divided into three different identities, respectively: entity user, realuser; guest, guest; anonymous user, anonymous user.
2. Command logging and log file logging
FTP can use the system’s syslogd for data logging, and the logged data includes the commands that the user has used and the user to transfer the data (transfer time, file size, etc.) of the record, so you can find the log information in the /var/log /var/log.
FTP transfers use the TCP packet protocol, and the FTP server uses two connections, a command (TCP21) channel and a data (TCP20) channel. Because they are TCP packets, both connections require three handshakes.
1, the process of establishing the command channel
The client will randomly obtain a port greater than 1024 or more with the FTP server side of the port21 to realize the connection, this process requires three handshakes. After the connection is realized, the client can execute commands on the FTP server through this connection, and commands such as querying file names, downloading, and uploading are executed using this channel.
2, the process of establishing a data channel
FTP connection mode: active mode (server-side active connection with the client), passive mode (client-side active connection with the server), active and passive is for the server.
(1) notify the FTP server to use the active connection and inform the port number of the connection
Port 21 of the FTP server is mainly used in the execution of commands, but when it comes to the flow of data, it is not the use of this connection. The client will tell the server how to connect if it needs data. If it is an active connection, the client will first enable a random port and tell the FTP server these two pieces of information through the command channel, and wait for the FTP server to connect.
What are the network protocols?
A network protocol is a collection of rules, standards, or conventions established for the exchange of data in a computer network.
For example, a microcomputer user in a network communicates with the operator of a mainframe computer, and because the two data terminals use different character sets, the commands entered by the operators are not recognized by each other.
In order to be able to communicate, each terminal is required to convert the characters in their respective character sets to the standard character set before they are transmitted into the network, and then to convert them to the characters in the terminal’s character set when they arrive at the destination terminal.
Of course, for incompatible terminals, in addition to the need to change the character set characters need to be converted to other characteristics, such as display format, line length, number of lines, screen scrolling, etc. need to be changed accordingly.