Sim300 dial-up Internet access and GPRS connection

Sim300 is a GPRS module embedded with TCP/IP protocol, which can implement GPRS communication and dial-up Internet access. In fact, I have not yet understood whether GPRS communication is a dial-up Internet access?

My board is composed of sim300 and STC single-chip microcomputer. In the single-chip microcomputer, a set of AT commands are sent to the sim300 module by a program, which can send data to the server with the public IP address. I have questions here. Can the server send data to the sim300 module? (Yes .) The same thing can be done with the serial port debugging Assistant of the PC. I have seen in many documents that the GPRS module requires at commands such as dial-up, but there is no need to dial-up, connect directly to the server and then send data. What is the reason for not dialing? My idea is: first, you do not need to dial up when you can connect to GPRS and send data. Dialing is only required when you dial up the Internet. Dial-up Internet access refers to the ability to browse Web pages through a browser. That is to say, GPRS connection is not the same as GPRS connection. In fact, if the module does not have the TCPIP protocol, if the microcontroller wants to send data to the network, it must also implement the PPP protocol in order to establish a connection with the mobile network. If the Protocol comes with it, the module will automatically encapsulate the data we send and then send it out. Second,
Sim300 has an embedded TCPIP protocol,
These operations are automatically completed in the module.

These two days I have an idea that I want to connect to the computer serial port through the sim300 module to achieve wireless Internet access through the sim300 module. That is
: How to Implement GPRS Modem dial-up Internet access through a serial port terminal. Because I do not understand the GPRS internet access process, I also sent the AT command through sim300 and single chip microcomputer communication. I saw the operation steps on the Internet: http://tech.sina.com.cn/s/2009-08-13/18501026701.shtml:

A serial port terminal can use the AT command to connect to the network carrier. However, if you want to successfully dial up the Internet, you cannot use the terminal because the PPP protocol is not implemented.
Why does a PC or an embedded operating system have a PPP protocol for GPRS internet access? It seems that to access the Internet, there must be a PPP protocol and dial-up is no doubt. I have been searching for it online for a long time.

The PDP activation information includes the PDP type, user name, password, Access Point (APN), and PDP address. ATD × 99 # there must still be protocol interaction after dialing. Call the PPP protocol stack after dialing and respond to the server message. PPP protocol. PAP and CHAP authentication is required.

 

The official information of Wavecom is explained as follows:
At + cgact = is to activate PDP and establish the connection between modem and GPRS network
At + cgdata = 1 is the data connection between the PC and the modem. In this connection, the modem is equivalent to the PPP server, and the PC is equivalent to the PPP client.
The Super Terminal does not seem to call the PPP protocol stack, so it will not respond to those messages and the connection will be disconnected. The above two connections can be established at the same time. Run the ATD * 99 *** 1 # command #
However, the connection is disconnected due to the same problem as above.

 

Port Monitoring Program.

 

1. The q24plus module should contain TCP/IP protocol. You can use a dedicated at command to connect to the server and send or receive data.
2. If it is only its modem, you need your CPU to complete the protocol, such as PPP, chap, TCP, UDP ......
3. q24plus supports open at, which means that the user program can reside in the module, but it is complicated. It is not clear in one or two sentences. Open at is an integrated development environment provided by Wavecom. It uses VC to write programs, generate download files, and download the program to the module of Wavecom for execution.

 

If you want to use a modem like a PC to access the Internet, you need to establish a PPP connection between the terminal and the modem.
You cannot manually enter the PPP connection process. The built-in TCP/IP protocol can send TCP/UDP data through the AT command. In fact, during the sending process, the modem has established a connection with the network, such as PDP activation, network connections and other Modem are automatically completed. Package Your data into IP data packets, or other packages, and then send them through GPRS.

 

1. Regard Wavecom as a computer. Wavecom q24pl002
Embedded PPP protocol. That is to say, through the AT command, Wavecom can dial GPRS by itself. Now you can think that q24pl002 is already working on a computer, but this computer
It is the CPU of 7.7. At this time, Wavecom has obtained a dynamic IP address and can use the TCP protocol for data interaction. Embedded protocols include UDP, FTP, SMTP, and POP3.

II,
Consider Wavecom as a modem. At this time, Wavecom q24pl002
That is, the role of modem.
You can call or send text messages through the AT command. To enable GPRS, you must enable the PC to implement dialing and other functions, that is, implement the PPP protocol on the PC side. Use the dial-up network provided by windows to complete the PPP connection. At this time, if you enter ATD * 99 *** 1 # On the Super Terminal, it makes no sense.

 

The GPRS module uses the AT command to dial data, such as China Mobile's "* 99 *** 1 #". If connect is OK, the physical layer is connected.
The next step is to connect the data link layer and the PPP protocol. The PPP protocol includes LCP (Link Control Protocol) and NCP (Network Control Protocol). After the physical layer is connected, you must first configure the data formats of the serial line through the LCP protocol, and the data transfer agreement between the two parties (see RFC for details), followed by the NCP protocol, NCP
It mainly obtains IP addresses and some specific conventions on IP packets in PPP encapsulation.

For the message flow of the session management layer, the context activation of PDP is exactly the same as that of ATD * 99. However, ATD * 99 # In addition to activating the PDP context, some internal statuses of the modem will also change,The at command State will not be retained, but will be switched to the group data receiving and receiving mode, so that PPP negotiation can be conducted.

 

After reading these words, I still understand a little bit.