Port OSI seven layer model data transfer

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The concept of port:

In Network technology, ports (port) have roughly two meanings:
One is the physical port, for example, ADSL Modem, hub, switch, router used to connect other network devices interface, such as RJ-45 Port, SC port and so on.
The second is the logical port, generally refers to the TCP/IP protocol port, the range of port number from 0 to 65535, such as for browsing the Web services 80 port, for the FTP service 21 port and so on.
What we're going to introduce here is the logical port.

divide by port number distribution:

(1) Well-known port (well-known Ports)
Well-known ports, known as port numbers, range from 0 to 1023, and these port numbers are generally fixed to some services. For example, 21 ports are assigned to the FTP service, 25 ports are assigned to the SMTP (Simple Mail Transfer Protocol) service, 80 ports are assigned to the HTTP service, 135 ports are assigned to the RPC (Remote Procedure Call) service, and so on.
(2) dynamic port (Ports)
Dynamic ports range from 1024 to 65535, and these port numbers are typically not fixed to a service, which means that many services can use these ports. As long as the running program makes a request to the system to access the network, the system can allocate one from these port numbers for the program to use. For example, port 1024 is assigned to the first program to send a request to the system. After the program process is closed, the port number that is occupied is freed.

divided by protocol type:

Divided by protocol type, it can be divided into TCP, UDP, IP and ICMP (Internet Control Message Protocol) and other ports. The following mainly describes TCP and UDP ports:

(1) TCP port
TCP ports, or Transmission Control protocol ports, require a connection between the client and the server to provide reliable data transfer. Common 21 ports include the FTP service, 23 ports for the Telnet service, 25 ports for the SMTP service, and 80 ports for the HTTP service, and so on.

(2) UDP port
UDP port, the user Packet protocol port, does not require a connection between the client and the server, and security is not guaranteed. Common network ports include the 53 port of the DNS service, 161 ports for SNMP (Simple Network Management Protocol) service, 8000 and 4000 ports used by QQ, and so on.

Common ports and their corresponding services

21 Ports: 21 ports are primarily used for FTP (file Transfer Protocol, document Transfer Protocol) services.
22 Ports: 22 ports are primarily used for SSH (Secure Shell, Shell Protocol) services.
23 Port: 23 port is primarily used for Telnet (remote login) services and is a common logon and emulator on the Internet.
25 Ports: 25 ports are open for SMTP (Simple Mail Transfer Protocol, Easy message Transfer Protocol) servers, primarily for sending mail, and today most mail servers use the protocol.
53 Port: Port 53 is open for DNS (domain name server, nameserver) server, mainly used for domain name resolution, and DNS service is the most widely used in NT system.
80 Ports: 80 ports are open for HTTP (Hypertext Transport Protocol, Hypertext Transfer Protocol), which is the most used protocol for surfing the Internet, primarily for protocols that transmit information on the WWW (World Wide Web) service.
443 Port: Port 443 is a web browsing port, primarily for HTTPS services, and is another HTTP that provides encryption and transmission over a secure port.
1024 Port: 1024 port is generally not fixed assigned to a service, the explanation in English is "Reserved" (reserved).
1080 Port: 1080 port is the port used by SOCKS Proxy service, and the WWW service used by everyone in the Internet is the Proxy service of HTTP protocol.
8080 Port: 8080 port with 80 port, is used for WWW Proxy service, can realize browsing Web page.

iOS seven-tier model and features

The process of data transfer

Transport Process Description:
Suppose a user wants to transfer data to a B user, and a user and B user are in two different network segments
1) The data request is sent from the application layer of a, transmitted to the presentation layer for data compilation and encryption, compression
2) Presentation layer sends data to the answering layer
3) The transport layer is used by the concept of the port number to identify services on the upper level, and to segment the services on top, and to maintain a communication connection between a-B and the reliability of the connection
4) package The data at the network layer and define the destination IP address and source IP address in front of the packaged data
5) Reprocessing at the data link layer, the data mask after processing defines the target Mac and source MAC address
6) Re-physical layer, eventually changing the data to machine and identification of the 10101 binary encoding, and then transmission on the network cable
7) to the router to the data forwarding, in order to extract the data information, the target IP network segment router is based on the IP address to forward data, so work in 3 layers, so received the packet, to first convert the binary code into a frame, and then convert the frame into an IP packet, IP packet destination address addressing
Convert the code into a frame, and then convert the frame to an IP packet, addressing the IP packet destination address
8) after confirming the corresponding transport interface according to the routing table, the data will be packaged for transmission.
9) b After receiving the data, unpack the packets in turn, receive the corresponding data, and vice versa.

Port OSI seven layer model data transfer