Main features of transport layer TCP and TCP connection

TCP The main features of the agreement

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TCP Is a connection-oriented transport layer protocol .（ Before the official data transmission, you need to send 3 A packet , This is called three handshakes , Negotiate parameters after establishing the connection , For example, how big is the cache , How many bytes are accepted for each segment ）

Every one of them TCP Connections can have only two endpoints （end point）, It can only be point-to-point （ one-on-one , Neither multicast nor broadcasting can work ）.

TCP Provide reliable delivery of services . in other words , adopt TCP Connect the transmitted data , No mistakes 、 No loss 、 Send in sequence without repetition .

TCP Provide full duplex communication .（ Once the sender and receiver have established a connection , Then you can use this connection for two-way communication ）

Byte stream oriented .TCP Medium “ flow ”（steam） A sequence of bytes flowing into or out of a process .（ Whether it's web pages or pictures , All in bytes 8 The bit , Put bytes into the cache one by one , What the application layer gives to the transport layer is the byte stream ,udp It's a message , All the content to be transmitted by the application is given udp agreement ）

 

 

 

IP The network provides unreliable transmission

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TCP Connection oriented transport layer protocol , Without connection 、 unreliable IP Provide reliable delivery services based on network services . So , stay IP Based on datagram service , Added a series of measures to ensure reliability .

 

 

 

TCP Byte stream oriented

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Segment bytes , Then add the first , The first part has the functions of numbering .

 

 

Be careful

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TCP A connection is a virtual connection, not a real physical connection .

TCP How many messages are sent to the application process at one time TCP We don't care .TCP According to the window value given by the other party and the current degree of network congestion, it determines how many bytes a message segment should contain （UDP The length of the message sent is given by the application process ）.

TCP Too long data blocks can be divided into shorter ones and then transmitted .

TCP It can also wait for enough bytes to accumulate before sending out the message segment .

 

 

TCP The connection of

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TCP Take connection as the most basic abstraction . Every one of them TCP The connection has two endpoints .

TCP The endpoint of the connection is not a host , It's not the mainframe IP Address , It's not the application process , It's not the protocol port of the transport layer .TCP The endpoint of a connection is called a socket （socket） Or socket .

The port number is spliced to （contatenated with）IP The address constitutes the socket .

 

Socket

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  One IP+ Port identification TCP One end , This is called socket .

 

 

 

TCP Connect IP Address Socket

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TCP Connection is an abstraction provided by protocol software .

TCP The end of the connection is a very abstract socket , namely （IP Address ∶ Port number ）.

The same IP There can be many different addresses TCP Connect . The same port number can also appear in multiple different TCP Connecting .