Difference Between TCP and UDP

--------- 1. connection-oriented TCP ---------

Connection orientation "means that a connection must be established with the other party before formal communication. For example, if you call someone else, you must wait until the line is connected and the other party picks up the microphone to talk to each other.

TCP (Transport Control Protocol) is a connection-based protocol. That is to say, a reliable connection must be established with the other party before sending and receiving data. A TCP connection can be established only after three "conversations". The process is very complicated. Here we only provide a simple and visual introduction. You only need to understand this process. Let's take a look at the simple process of the three conversations: host a sends a connection request packet to host B: "Can I send data to you ?", This is the first conversation; host B sends a packet to host a that agrees to the connection and requires synchronization (synchronization means that two hosts are sending, receiving, and coordinating): "Yes, when will you send it? ", This is the second conversation. host a sends another packet to confirm that host B's request is synchronized: "I will send it now, let's proceed !", This is the third dialogue. The purpose of the three "dialogs" is to synchronize the transmission and receipt of data packets. After the three "dialogs", host a formally sends data to host B.

TCP protocol can be appliedProgramA reliable communication connection is provided, so that the byte stream sent by a computer is sent to other computers on the network without error. Data Communication Systems with high reliability often use the TCP protocol to transmit data.

--------- 2. Non-connection-oriented UDP protocol ---------

Non-connection oriented "means that you do not need to establish a connection with the other party before the formal communication, and send the connection directly regardless of the other Party's status. This is very similar to the popular mobile phone text message: when you send a text message, you only need to enter the phone number of the other party and then OK.

User Data Protocol (UDP) is the protocol corresponding to TCP. It is a non-connection-oriented protocol. Instead of establishing a connection with the other Party, it directly sends data packets!

UDP is applicable to applications that transmit only a small amount of data at a time and do not require high reliability. For example, we often use the "ping" command to test whether the TCP/IP communication between two hosts is normal. In fact, the principle of the "ping" command is to send UDP packets to the other host, then, the host of the other party confirms that the packet is received. If the message indicating whether the packet arrives is returned in time, the network is connected. Because the UDP protocol does not have a connection process, its communication performance is high; but also because of this, its reliability is not as high as that of the TCP protocol. Qq uses UDP to send messages, so sometimes messages cannot be received.

TCP and UDP have their own strengths and weaknesses, and are suitable for communication environments with different requirements.

--------- 3. Differences Between TCP and UDP ---------

TCP UDP
Connection-oriented non-connection
Reliable and unreliable Transmission
Transmit a large amount of data and a small amount of data in applications
Slow and fast

--------- 4. By port number can be divided into three categories :---------

(1) well known ports: from 0 to 1023, they are closely bound to some services. Usually the communication between these ports clearly indicates a service protocol. For example, port 80 is always HTTP Communication.

(2) Registration port (registered ports): from 1024 to 49151. They are loosely bound to some services. That is to say, many services are bound to these ports, which are also used for many other purposes. For example, many systems process dynamic ports starting from around 1024.

(3) dynamic and/or private ports: From 49152 to 65535. Theoretically, these ports should not be allocated to the service. In fact, machines usually allocate dynamic ports from 1024. But there are also exceptions: Sun's rpc port starts from 32768.

(4) 0 is usually used to analyze the operating system. This method works because "0" is an invalid port in some systems. When you try to use a normally closed port to connect to it, different results will be generated. A typical scan: an IP address of 0.0.0.0 is used to set the ACK bit and broadcast it on the Ethernet layer.