Detailed TCP and UDP

A, TCP features

• Connection-oriented, reliable transport layer protocol based on the byte stream.
• The application layer is divided into segments, and the target node transmits the TCP layer send.
• It has a number of data packets, the other received the acknowledgment ACK is transmitted, retransmission is not received.
• Use efficacy and efficiency if the experimental data to error during transmission.

Two, TCP packet information

　　Packet header contains information include:

• Source port, destination port
• Marking process (socket): IP address + protocol + port number

　　The TCP flags mark:

1. URC: urgent, urgent pointer is effective when 1;
2. ACK: acknowledgment sequence number flag;
3. PSH: push sign, do not enter the data cache, directly to the application;
4. RST: Reset the connection flag;
5. SYN: synchronization sequence number, the process for establishing a connection;
6. FIN: finish flags to release the connection.

Three, TCP three-way handshake

Flow chart below (painted by Yo - Recommended tools: online at ProcessOn):

 

TCP three-way handshake flow chart Details:

1. When connection is established, the client sends a SYN packet (seq = x) to the server, and enter SYN-SEND state, the server waits for acknowledgment.
2. Server receives a SYN packet, the client must confirm SYN (ack = x + 1), at the same time, they would send a SYN packet (seq = y), i.e., SYN + ACK packet and the SYN-RECV state into the server.
3. Client receives the SYN + ACK packet to the server, the server sends an acknowledgment packet ACK (ack = y + 1), this packet is sent, the client and the server into ESTABKISHED state. Start data transmission.

Four, TCP's four wave

 

TCP flow chart four times and waved Details:

1. After the client sends a FIN, for closing the data transfer service to the client, client enters FIN-WAIT-1 state.
2. After receiving the FIN service, transmits an ACK to the Client, the acknowledgment number of the received seq + 1 (the same SYN, FIN a occupy a sequence number), service into the CLOSED-WAIT.
3. sending a service FIN, for closing the data transfer service to the client, service into the LAST-ACK state.
4. After the client receives the FIN, client enters TIME-WAIT state, then sends an ACK to-Service, the acknowledgment number of the received sequence number +1. service enter CLOSED state, completed four times and waved.

Five, TCP sliding window

Role: ① to ensure the reliability of TCP;

　　　② ensure that the flow control characteristics of TCP (transmission data sequence).

Six, UDP characteristics

• For non-connection
• Does not maintain a connection state, supports simultaneous transmission of multiple clients want the same message
• Only the packet header 8 bytes, an additional small opening
• Restricted to only certain data generation rate, the transmission rate and performance of the machine
• Do our best to interact, does not guarantee reliable delivery, does not maintain a connection status table
• Oriented message, the message does the application submitted by the split and merge

Seven difference, TCP and UDP

• For connection / connectionless
• Reliable / Unreliable
• Packet order / disorder
• speed
• Middleweight