Reuse and distribution

Multiplexing and demultiplexing are the services that the transport layer protocol must provide .

Multiplexing and multiplexing are common in the process of network transmission , Unique to the non transport layer .

1.  An example

host1 Of p3 Process to host2 Of p1 Process transfer information , meanwhile host3 Of p4 Process also to host2 Of p2 Process transfer information .

For the receiver , The transport layer at the receiving end identifies the arriving multiple transport layer messages , extract socket Information , Locate the message segment to the corresponding socket On , The process is called Demultiplexing .

For the sender , From different socket Collect information and add the first part , Send it through the network layer , be called Multiplexing .

2. The specific working mode of multiplexing

The host receives a IP The datagram , The IP Datagram carry Source IP Address and Purpose IP Address . Yes IP After the datagram is unpacked, a transport layer segment,segment There is Source port number and Destination port number , Corresponding Source process and Destination process , The transport layer protocol distributes data correctly according to the port number .

3. Connectionless distribution （UDP）

Features of connectionless distribution ：

• establish socket, And will socket Bind to a port number ,UDP Use Purpose IP Address and Destination port number The unique identifier of a binary socket
• Host received UDP After paragraph , Check the destination port number ,UDP The segment is connected to socket.
• From different hosts and transmitted to the same process UDP Segments will be connected to the same socket On .

 4. Connection oriented distribution （TCP）

  Connection oriented features ：

• TCP Adopt include Source IP Address 、 Source port number 、 Purpose IP Address 、 Destination port number To identify socket.
• TCP The protocol is connection oriented （ Point to point ） agreement , Reflected in the transport layer is that the receiving process will be from each different source TCP Segment creation socket.

Multi process connection oriented sharing ：

 

Due to the high cost of creating and maintaining processes , Usually the server will adopt a lower cost method , That is to create a process Multiple threads To communicate with clients , Each thread will have its own socket.

Multithreaded connection oriented sharing ：