TCP
TCP (Transmission Control Protocol) is one of the most commonly used transport layer protocols in computer networks, which provides reliable, connection-oriented data transmission services. TCP is responsible for segmenting application-layer data into appropriate packets and ensuring that these packets arrive at the destination host in the correct order. The following is a detailed introduction to the characteristics, working mechanism and key concepts of TCP:
Features and Benefits:
-
Reliability: TCP ensures reliable data transmission through sequence numbers, acknowledgment responses, and retransmission mechanisms, and can recover lost data even in the event of network congestion or packet loss.
-
Connection-oriented: TCP establishes a virtual, full-duplex connection to ensure that the two communicating parties can communicate with each other, and close the connection after the data transmission ends.
-
Flow Control: TCP uses a sliding window mechanism to control the rate at which data is sent and received to avoid congestion of data packets in the network.
-
Congestion control: TCP can detect the degree of network congestion and reduce the sending rate accordingly to avoid network congestion.
-
Sequence guarantee: TCP ensures that data packets arrive at the destination host in the correct order, even if the data packets are out of order during transmission, they will be reordered.
TCP working mechanism:
-
Three-way handshake: When establishing a TCP connection, the client sends a data packet with the SYN (synchronization) flag to the server, and the server replies with a packet with the SYN and ACK (confirmation) flags after receiving it, and finally the client replies with another ACK packet, so the connection is established.
-
Data transfer: Data is split into appropriate packets on the TCP connection, each packet has a sequence number. The receiving end tracks the sequence and loss of data packets through acknowledgments and sequence numbers.
-
Flow and congestion control: TCP uses a sliding window mechanism to control the rate at which data is sent and received, avoiding buffer overflow at the receiver caused by the sender's speed being too fast. In addition, TCP also uses congestion control algorithms to avoid network congestion.
-
Wave four times: When closing the TCP connection, first one party sends a data packet with the FIN flag, the other party replies with an ACK packet, then the sender sends another packet with the FIN flag, and finally the receiver replies with an ACK packet, The connection is thus terminated.
Key concepts of TCP:
-
Sequence and acknowledgment numbers: Every TCP packet has a sequence number that indicates where the packet is in the data stream. Acknowledgment numbers are used to acknowledge data that has been received.
-
Sliding Window: A sliding window is the size of the window between the sender and receiver to control the rate of data flow.
-
Timeout and retransmission: If the sender does not receive an acknowledgment, it will consider the packet lost and trigger a retransmission mechanism.
-
MSS (Maximum Segment Size): MSS represents the maximum size of a TCP packet, which depends on the maximum transmission unit (MTU) of the network.
UPD
UDP (User Datagram Protocol) is another commonly used transport layer protocol. Compared with TCP, it is simpler, but it does not provide the reliability and connectivity of TCP. UDP is usually used in application scenarios that require high real-time performance but do not require reliable transmission. The following is a detailed introduction about UDP:
Features and Benefits:
-
No connection: UDP is a connectionless protocol. After the sender sends the data packet, it does not need to wait for the confirmation response from the receiver. This makes UDP more lightweight, but also means that packets can be lost, duplicated, or out of order in transit.
-
Fast: Since UDP does not need to establish and maintain connections, it is generally faster than TCP. This makes it suitable for real-time applications such as audio and video transmission and online gaming.
-
Low latency: Since UDP does not have TCP's congestion control and flow control mechanism, its latency is low. But it can also lead to poor performance when the network is congested.
-
Broadcast and multicast: UDP supports broadcast and multicast transmission, which means that a data packet can be sent to multiple target hosts at the same time, which is suitable for one-to-many communication.
UDP working mechanism:
-
Data encapsulation: The data of the application layer is divided into UDP data packets, and each data packet contains the destination port number and source port number information.
-
Data transmission: Data packets are transmitted over the network, but the order of data packets, transmission reliability are not guaranteed, and no retransmission mechanism is provided.
-
Data reception: The receiver receives the data packet according to the port number and extracts the data from it.
Applicable scene:
UDP is suitable for the following scenarios:
-
Real-time applications: Due to the low-latency nature of UDP, it excels in real-time applications, such as online gaming, video chat, and real-time audio transmission.
-
Broadcast and multicast: UDP supports broadcast and multicast transmission, suitable for sending data to multiple hosts at the same time.
-
Short Messaging: When an application only needs to send short control messages or data packets, UDP can provide an efficient solution.
-
Simple data transfer: If the application can tolerate lost data and requires the lowest possible overhead, UDP can be an appropriate choice.
the difference
TCP (Transmission Control Protocol) and UDP (User Datagram Protocol) are two different transport layer protocols used to transmit data in computer networks. They differ greatly in their characteristics, uses, and how they work. Following are the main differences between TCP and UDP:
1. Connectivity and reliability:
- TCP is a connection-oriented protocol. It establishes a connection through a three-way handshake to ensure the reliability of data transmission, and provides error detection, flow control, congestion control and retransmission mechanisms. It is suitable for scenarios that need to ensure that data is not lost, not repeated, and ordered. .
- UDP is a connectionless protocol that does not establish a connection, does not provide reliability guarantees, and does not guarantee the order and transmission of data. It is suitable for data transmission that requires high real-time performance and allows loss, such as audio and video transmission, real-time games, etc.
2. Transmission speed and efficiency:
- Since TCP provides reliability guarantees, it will introduce some additional overhead, resulting in slower transmission speeds, and is suitable for scenarios that do not require speed but require data integrity.
- UDP does not have the complex mechanism of TCP, and has a fast transmission speed. It is suitable for scenarios that require high real-time performance and can tolerate a small amount of data loss.
3. Packet order:
- TCP will ensure that data packets are transmitted in the correct order, and if any data packets are lost, they will be resent to ensure the order of data.
- UDP does not guarantee the order of data packets, and data packets may be transmitted out of order, requiring the application layer to deal with the order of data.
4. Congestion control:
- TCP has a congestion control mechanism, which can reduce the data transmission rate when the network is congested, so as to avoid network collapse.
- UDP has no congestion control and packets can cause network problems when congested.
5. Applicable scenarios:
- TCP is suitable for scenarios that need to ensure data reliability, such as web browsing, file transfer, email, etc.
- UDP is suitable for scenarios that require high real-time performance and can tolerate a small amount of data loss, such as real-time games, audio and video transmission, and VoIP.