Introduction to TCP transmission control protocol

In the use of the Internet, the most basic protocol stack is the TCP/IP protocol stack. The basic protocols are TCP transmission control protocol and IP Internet protocol. Next, we will introduce the concept and basic structure of the two parties, as well as their functions.

TCP: Transmission Control Protocol

TCP is a connection-oriented) Reliable, byte stream-based Transport layer (Transport layer) communication protocol, defined by RFC 793 of IETF ). In the simplified computer network OSI model, UDP is another important transmission protocol in the same layer.

In Internet protocol suite (Internet protocol suite), the TCP layer is located on the IP layer and the middle layer under the application layer. Different Host application layers often require reliable connections like pipelines, but the IP layer does not provide such a stream mechanism, but provides unreliable packet switching.

The Application Layer sends an eight-byte data stream for inter-network transmission to the TCP layer, TCP then splits the data stream into packets of an appropriate length, which is usually limited by the maximum transmission unit (MTU) at the data link layer of the network connected to the computer ). Then, TCP sends the result packet to the IP layer, which transmits the packet to the TCP layer of the receiver entity through the network.

To ensure that no packet loss occurs, TCP sends an serial number to each byte, and the serial number also ensures that packets transmitted to the receiving end are received in sequence. Then, the receiver entity sends back an ACK message to the successfully received bytes. If the sender entity does not receive the ACK message within the reasonable round-trip delay (RTT, if the corresponding data is lost, the data will be re-transmitted. TCP uses a checksum function to check whether there is any data error. The Checksum is calculated during sending and receiving.

First, after the TCP connection is established, both parties can transmit data at the same time, and secondly, it is full-duplex. In terms of reliability, timeout retransmission and RST validation mechanisms are used.

In terms of traffic control, the sliding window protocol is used, which stipulates that unconfirmed groups in the window need to be re-transmitted.

In terms of congestion control, the slow start algorithm is used.

What is TCP/IP?

TCP/IP (Transmission Control Protocol/Internet Protocol) is an industrial standard Protocol set designed for WANs. It was developed by research institutions of the ARPANET network.

Sometimes we describe TCP/IP as an Internet Protocol set "Internet Protocol Suite", and TCP/IP is one of the two Protocols (which will be introduced later ). As TCP/IP is a familiar protocol, TCP/IP or IP/TCP is used to replace the entire Protocol set. This is a bit strange, but there is no need to argue about this habit. For example, sometimes we discuss that NFS is based on TCP/IP, although it doesn't use TCP at all (only IP, and another interactive protocol UDP instead of TCP ).

Internet is a collection of networks, including ARPANET, NSFNET, lan distributed across regions, and other types of networks, such as (DDN, Defense Data Network, US Defense Data Network ), these are collectively referred to as Internet. All these networks are interconnected. (Because most basic network protocols are developed by DDN, sometimes DDN and Internet have the same meaning in a sense ). Users on the network can transmit information to each other, except for some authorization restrictions and security considerations. Generally, the Internet protocol file is a basic standard adopted by the Internet Committee. TCP/IP standards are developed by "public opinion" rather than by the Committee. Anyone can provide a document that is published in RFC (Request for Comment requirement Comment.

Standard Transmission Control Protocol (TCP/IP) and inter-network protocol (CEN) are published in a series of documents called RFC. The document is edited and revised by technical experts, special working groups, or RFC. When a document is published, it is assigned an RFC volume, for example, RFC959 indicates FTP, RFC793 indicates TCP, RFC791 indicates IP, etc. The original RFC is retained and never updated. If the document is modified, the document will be published with a new number. Therefore, it is important to confirm that you have the latest RFC document about a specific topic. The main RFC document numbers are listed later.