Introduction to TCP Association
TCP protocol (Transmission Control Protocol) and IP protocol (Internet Protocol) are two important protocols in computer networks. They play a key role in Internet communications.
The TCP protocol is a transport layer protocol built on the IP protocol to provide reliable, connection-oriented data transmission. The TCP protocol uses port numbers to identify different applications or services. It transmits data by creating a virtual connection and uses sequence numbers and confirmation mechanisms to ensure the reliability and sequential delivery of data.
The main features of the TCP protocol include:
- Reliability: The TCP protocol uses a confirmation mechanism and a retransmission mechanism to ensure reliable transmission of data. The receiving end will confirm the received data and notify the sending end whether the lost data needs to be retransmitted.
- Flow control: The TCP protocol uses a sliding window mechanism to control the data sending rate of the sender in order to adapt to the processing capabilities of the receiver and avoid overload or resource waste.
- Congestion control: The TCP protocol detects network congestion through the congestion window algorithm and adaptively adjusts the sending rate to reduce the impact of network congestion.
- Connection-oriented: After the two communicating parties establish a connection, the TCP protocol uses three-way handshakes and four-way waving to ensure the reliable establishment and closing of the connection.
To sum up, the IP protocol provides basic data packet transmission functions and routing selection, and the TCP protocol provides reliable, connection-oriented data transmission on this basis. Together they form the infrastructure of Internet communications.
Introduction to IP protocol
The IP protocol is a network layer protocol responsible for transmitting data packets over the Internet. The IP protocol uses IP addresses to identify devices on the network (such as computers, routers, etc.). It sends packets from a source device to a destination device, traveling through a series of routers and network links. The IP protocol works in a connectionless manner. Each data packet is sent independently and no persistent connection is established.
The main functions of the IP protocol include:
- Address Assignment: Each device is assigned a unique IP address to locate and communicate on the network.
- Routing: Select the appropriate path and next-hop router based on the destination IP address to transmit the packet to the destination device.
- Fragmentation and reassembly: Fragment large packets into smaller packets for transmission over the network and reassemble into the original packets on the target device.
Introduction to ports
A port is a logical communication endpoint in a computer network that identifies a network application or service. In a TCP/IP network, the port number is a 16-bit integer ranging from 0 to 65535.
There are two types of ports: system ports and dynamic ports.
System ports (or well-known ports) are ports reserved for some common network services, ranging from 0 to 1023. For example, HTTP services usually use port number 80, FTP services use port number 21, SSH services use port number 22, etc. These port numbers are already pre-assigned to the corresponding service in most operating systems.
Dynamic ports (or private ports) are port ranges that are temporarily assigned to client applications. The range is from 1024 to 65535, they do not belong to any specific service or application. When a client application establishes a connection with the server, the operating system dynamically assigns an available port number to the connection.
By associating a packet's source and destination ports with the destination IP address, a computer network can deliver the packet to the correct application or service. When the data packet reaches the target device, the operating system will pass the data packet to the corresponding application for processing based on the target port number.
The choice of port number is usually determined by the application. For server-side applications, they need to listen to a specific port number so that they can accept connection requests from clients. The client application usually dynamically selects an available port number to establish a connection with the target server.
It should be noted that the port number and IP address together form the address that uniquely identifies an application or service on the network. When communicating over the network, it is important to ensure that the correct port number is used.
To summarize, a port is a logical communication endpoint used to identify a network application or service. It is used in conjunction with IP addresses to allow network data to be accurately delivered to the correct application or service. System ports are port ranges reserved for specific services, while dynamic ports are port ranges temporarily assigned to client applications.