The main functions of the TCP protocol are: 1. Complete the confirmation of datagrams, flow control and network congestion; 2. Automatically detect datagrams and provide the function of error retransmission; 3. Transmit multiple paths The datagrams are arranged in the original order; 4. Control timeout retransmission and automatically adjust the timeout value.
TCP(Transmission Control Protocol) is a connection-oriented, reliable, byte stream-based transport layer Communication protocol, defined by IETF's RFC 793. In the simplified OSI model of computer networks, it completes the functions specified by the fourth layer transport layer. User Datagram Protocol (UDP) is another important transport protocol within the same layer [1]. In the Internet protocol suite, the TCP layer is an intermediate layer located above the IP layer and below the application layer. Reliable, pipe-like connections are often required between application layers of different hosts, but the IP layer does not provide such a flow mechanism, but provides unreliable packet switching.
When the application layer sends a data stream represented by 8-bit bytes for inter-network transmission to the TCP layer, TCP divides the data stream into message segments of appropriate length. The maximum transmission segment size (MSS ) is usually limited by the maximum transmission unit (MTU) of the data link layer of the network to which the computer is connected. TCP then passes the data packet to the IP layer, which delivers the packet through the network to the TCP layer of the receiving entity.
In order to ensure the reliability of message transmission, TCP gives each packet a sequence number. At the same time, the sequence number also ensures that the packets transmitted to the receiving end entity are received in order. The receiving entity then sends back a corresponding acknowledgment (ACK) for the successfully received bytes; if the sending entity does not receive the acknowledgment within a reasonable round trip delay (RTT), then the corresponding data (assumed to be lost) will be retransmitted.
TCP protocol and IP protocol together form the TCP/IP protocol. TCP/IP is a set of protocols used for computer communication. We usually call it the TCP/IP protocol family. It is a network architecture and protocol standard developed by the U.S. Department of Defense for its ARPANET wide area network in the mid-1970s. The INTERNET built on it is currently the largest computer network in the world. It is precisely because of the widespread use of INTERNET that TCP/IP has become the de facto standard. The reason why TCP/IP is a protocol family is because the TCP/IP protocol includes TCP, IP, UDP, ICMP, RIP, TELNETFTP, SMTP, ARP, TFTP and many other protocols. These protocols are together called the TCP/IP protocol.
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