Shulou(Shulou.com)06/03 Report--

For example, you use QQ to send a text message "Hello" to the other person.

Sending process:

1. QQ first converts "Hello" into ASCII code, and generates a message: (QQ header) + (Hello ASCII code)

2. QQ is the application layer software. In theory, the application layer should give the message to its next layer, the presentation layer. Now the message becomes (presentation layer header) + (QQ header) + (Hello ASCII code)

However, I think QQ should send the message directly to the UDP protocol of the transport layer, and the message becomes (UDP header) + (QQ header) + (Hello ASCII code). At this point, a UDP connection will also be established, without further discussion.

3. Then the UDP protocol gives the message to the IP protocol of the network layer, and the message becomes (IP header) + (UDP header) + (QQ header) + (Hello ASCII code).

4. Then, the IP protocol sends the message to the Ethernet protocol of the link layer protocol, and the message becomes (Ethernet header) + (IP header) + (UDP header) + (QQ header) + (Hello ASCII code).

5. Then, the Ethernet message is sent to the network card, where the message is divided into several frames and sent to the network through the physical layer in the form of 0101.

6. Then, the switch receives these frames and restores them to Ethernet messages. The switch looks up its own MAC address table according to the MAC address in the Ethernet header, finds the interface, and sends the message out of the exit interface (sending the message to the gateway device). When the message is sent, the message is divided into multiple frames and sent through the physical layer.

7. After receiving the message, the gateway looks up its own routing table and FIB table according to the IP address in the header of the IP message, finds the next hop address, and then sends the message to the next hop. This process is repeated until the other party's gateway is found.

8. The gateway of the other party sends the message to the computer of the other party.

9. After receiving the message, the other computer strips off the Ethernet header, the IP header, and the UDP header in turn, and then finds that the application layer protocol is QQ, so it is handed over to the QQ software for processing, and QQ restores the ASCII code to "Hello", which is displayed in the dialog box.

That's the general process.

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