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Fundamentals of the Internet

TCP/IP protocol

TCP/IP (Transmission Control Protocol/Internet Protocol) is a network communication protocol that regulates all communication devices on the network, especially the format and transmission method of data between one host and another. TCP/IP is the basic protocol of the internet and a standard method for packetizing and addressing computer data. In data transmission, it can be visually understood that there are two envelopes, TCP and IP are like envelopes, the information to be transmitted is divided into several segments, each segment is stuffed into a TCP envelope, and the segment is recorded on the envelope. The information of the segment number, and then stuff the TCP envelope into the IP large envelope, and send it to the Internet. At the receiving end, a TCP software package collects the envelope, extracts the data, restores it in the order before sending, and checks it. If an error is found, TCP will ask for retransmission.

The TCP/IP protocol is actually a layered model, consisting of four conceptual layers, namely the network interface layer, the Internet layer, the transport layer and the application layer.

Network interface layer: It is the bottom layer of TCP/IP, corresponding to the data link layer of OSI, and is responsible for receiving IP data and sending it to the selected network.

OSI - Open System Interconnection Reference Model (Opensysteminterconnectionreferencemodel). The reference model developed by the International Organization for Standardization (ISO) recommendations.

Internet layer (interconnect layer): Corresponds to the network layer of OSI. Receive the packet data from the transport layer, encapsulate it into a datagram, fill in the data header, and use the routing algorithm to send the data to the corresponding network interface.

Transport layer: Also known as the TCP layer, it provides reliable transmission services for the application layer to ensure that data arrives in order without errors.

Application layer: Provide various application services, such as email, file transfer, remote login, etc.

1. IP protocol

The IP protocol is the most basic transport protocol on the Internet, providing unreliable connectionless services.

Unreliable: means that data packets cannot be guaranteed to be delivered correctly to the destination, packets may be lost, duplicated, delayed or delivered out of sequence, and the service does not detect or notify senders and receivers;

Connectionless: means that each packet is processed independently and may go through different paths, some may be lost, and some may arrive.

The IP protocol has three functions: it specifies the data format transmitted on the Internet; it completes the routing function; IP contains a set of rules for unreliable packet transmission.

1. TCP protocol

The TCP protocol is located above the IP layer protocol and is a connection-oriented protocol. The so-called connection-oriented means that both endpoints need to agree to connect in order to communicate. TCP hands over the data packets to be transmitted to the IP layer for implementation. TCP has the ability to recover lost packets and has the function of automatic retransmission. Therefore, it has an error correction function. The combination of TCP and IP effectively guarantees the smooth flow of data on the Internet.