Transport layer uses sliding window to realize flow control

Sliding window mechanism

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Traffic buffering ： Solve the speed mismatch problem （ Client and server , The speeds at these two ends are completely inconsistent , Inconsistent machine performance , At this time, the processing speed is not matched ）

TCP Use sliding window to realize flow control . Flow control is to control the sending rate of the sender , To ensure that the receiving party can receive .

TCP Both sides of the session maintain a sending window and a receiving window . The size of the receive window depends on the application 、 System 、 Hardware limitations . The sending window depends on the receiving window of the peer notification .

In the confirmation message sent by the receiver window Field can be used to control the size of the sender's window , Thus, the transmission rate of the sender is affected . Send the receiver's confirmation message window Field set to 0, Then the sender cannot send data .

TCP Header contains window Field ,16bit position , It represents the byte capacity of the window , The maximum is 65535. This field tells the sender how many buffers it has to receive data . So the sender can send data according to the processing power of the receiver , The receiver will not be unable to handle it . The size of the receiving window is approximately equal to the size of the transmitting window .

Flow control means that the sender sends to the receiver too fast , The receiver can tell it to slow down .（ Sliding window to achieve flow control , Flow control is that the receiver controls the sender ）

Receiving end setting window , The sending end sets the sending window according to the window of the receiving end , The window can be adjusted during the whole communication process .

There are window fields when the above connection is established 64240 Bytes , The largest data segment is 1460, The maximum transmission unit of the network card MTU The largest transmission unit in the data link layer is 1500 Bytes , The first part of the network layer is 20 Bytes , The first part of the transport layer is 20 Bytes , Then the data becomes 1460 Bytes . So slide the window 64240/1460 You can send it continuously 44 A packet .

At the same time, it can also support selective confirmation SACK_PERM=1.

In establishment TCP These parameters can be negotiated when connecting , How big is the receiving window ,MSS How much is the , Then support selective confirmation .

Confirm that the length of the data inside is 0 Of , The window size is specified when the confirmation is given , You can see that the window can be resized . When the receiving window becomes smaller, the sending window becomes smaller , The sender doesn't send it so fast .

 b tell a, Its acceptance window is 400, The maximum length of the segment is 100 Bytes , In the hair 1 2 here we are 3 lost , Confirm it , Let it send a third packet , Then the window starts moving , Then send a message 4 5 A second time 3 individual , Confirm to it after receiving ........

The window becomes 0 After that, I stopped sending it , The sender stops , Send confirmation after processing , The window is adjusted to 400.