A part of the data link layer, which provides a mechanism for transferring PGN with data of 9 bytes or more.[3]
Each layer in the transport protocol provides for the upper layerbusinessFunction.In order to provide this service function, the next layer merges the data in the previous layer into the data domain of this layer, and then implements the service function of this layer by adding header or footer. This process is calledData encapsulation。The user's data should be packaged again and again, and finally converted into signals that can be transmitted on the network and sent to the network.When the target computer is reached, the reverse unpacking process is performed.This is similar to writing a letter in daily life. Write your meaning on a piece of paper. If you are interested, fold the paper into a special shape, put it in an envelope and seal the mouth. Write the recipient's address, postal code and name, and then stick a stamp. The staff of the post office will stamp it and send it to the post office where the recipient is located,The postman delivers the letter to the addressee according to the address on the letter, and the addressee opens the letter to read its contents.
This is similar to writing a letter in daily life. Write your meaning on a piece of paper. If you are interested, fold the paper into a special shape, put it in an envelope and seal the mouth. Write the recipient's address, postal code and name, stick a stamp on it, and the post office staff will seal itpostmarkSend it to the post office where the recipient is located. The postman gives the letter to the recipient according to the address on the letter. The recipient opens the letter and reads its contents.[1]
The lower layer can provide services to the upper layer in two forms: connection oriented services (TCP) and connectionless services (UDP).
TCP: Transmission control protocol, which can automatically correct errors in transmission;
UDP: User packet protocol. When an error occurs in the transmissionerror messagediscard;
UDP mode is more powerful than TCP modeFault toleranceIf UDP is used, its buffering speed is 45% faster than TCP, and it can greatly save network sharing bandwidth. When the network is unstable, buffering will not often occur, so many movie and television programs are transmitted in UDP mode.[1]
Rules that both parties must follow in data transmission.
Basic elements
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（1）addressing。When an application wants to transfer data with another application, it must indicate which application it is connected to.addressingThe method of defining the transmission address is generally adopted.Internet transport address is composed of IP address andhostPort numberform.
(2) Establish a connection.In actual network applicationsThree handshakesAnd add some conditions to ensure a reliable connection.The added condition is: sentmessageThere must be increasingserial number；Set a timer for each message and set a maximum delay. Messages that exceed the maximum delay but still do not receive acknowledgement are considered lost and need to be retransmitted.
Simple File Transfer ProtocolOr calledMini File Transfer Protocol(English:TrivialFileTransferProtocol，abbreviationTFTP）, a simplified file transfer protocol, was defined in 1980.[1]
Small file transfer protocols were very simple and could be easily implemented with a small amount of memory - an important consideration at the time.So TFTP is used to boot computers, such as routers without mass storage.It is still used to transfer small files between hosts on a network, such as booting a remote X Window System terminal or other thin clients from a network host or server.[1]
The small file transfer protocol is based on the earlier file transfer protocol, which is a part of the general packet protocol (PUP Protocol).In the early work of TCP/IP protocol group, TFTP is often the first protocol to complete on a new host type - because it is very simple.[1]
The earliest version of the small file transfer protocol was before RFC 1350, which showed quite bad protocol defects. When it was discovered, it was called the Magic Novice Syndrome.[1]
Network transmission protocol
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Network transmission protocolOr referred to asTransport Protocol（Communications Protocol）, refers to the common language of computer communication or network equipment.Now the most popular computer communication is network communication, so "transmission protocol" generally refers to the transmission protocol of computer communication,[1]Such as TCP/IP, NetBEUI, DHCP, FTP, etc.However, transport protocols also exist in other forms of computer communication, such as communication between objects in object-oriented programming;The messages between different programs in the operating system need to have a transmission protocol to ensure that both parties can communicate without interruption.[1]
File Transfer Protocol
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File Transfer Protocol(English:FileTransferProtocol，abbreviation:FTP）It is a set of standard protocols for file transfer on the network.It belongs to the application layer of network transmission protocol.[1]
FTP is an 8-bit client server protocol that can operate any type of file without further processing, just like MIME or Unicode.However, FTP has a very high latency, which means that the time between the start of the request and the first receipt of the required data will be very long;And from time to time, some lengthy login process must be executed.[1]
