With the deepening of the network era, the Internet has become an important basic information facility. More and more devices need to access the Internet. For some embedded intelligent systems such as PDAs, it is necessary to realize wireless communication. Dial-up Internet access is one of the ways for household appliances to use the Internet to achieve intelligence. Currently, among the many ways to access the network, the more economical and practical way is to connect to the ISP's access mode through dial-up. The data link layer protocol used in this mode is mainly PPP. This paper analyzes the PPP negotiation process of dial-up Internet, and deeply studies the design of network dialing function program, and verifies it on the embedded hardware platform based on ARM9 processor. 1 System hardware platform construction This article uses the ARM920T core based chip S3C2410X, which is a 32-bit embedded RISC microprocessor introduced by ARM. The processor is targeted at handheld devices and cost-effective, low-power applications. The wireless communication module uses a GPRS module. Wavecom Q2403A is a wireless modem that transmits data based on GPRS network. It can realize voice call, short message service and data transmission. The Q2403A provides users with a variety of interfaces, including power connectors, LCD interfaces, SIM card interfaces, charger interfaces, headphone jacks, microphone jacks, and a variety of peripheral interfaces for other special purposes. When Q2403A sends data via GPRS, the download speed is 26.8 Kb/s and the upload speed is 13.4 Kb/s. The hardware structure of the system based on ARM microprocessor is shown in Figure 1. 2 network dial-up connection process In many ways of accessing the network, this article uses GPRS as an example to illustrate the specific network dial-up connection process. Network dial-up access to the Internet is to use the PPP protocol to create a connection, using GPRS for data transmission. The PPP link establishment process is divided into a creation phase, an authentication phase, and a network negotiation phase. (1) Create a PPP link The Link Control Protocol (LCP) is responsible for creating links. At this stage, the basic communication method will be selected. (2) User verification At this stage, the client sends its identity to the remote access server. This phase uses a secure authentication method to prevent third parties from stealing data or impersonating remote clients to take over connections with clients. Advance from the authentication phase to the network layer protocol phase is prohibited until the authentication is completed. If the authentication fails, the authenticator should transition to the link termination phase. The most commonly used authentication protocols are the password authentication protocol PAP (Password AuthenTICaTIon Protoc01) and the IP option and IPCP (Internet Protocol Control Protocol). (3) Call the network layer protocol After the authentication phase is completed, PPP will invoke the Network Control Protocol (NCP) selected in the link creation phase. The selected NCP resolves high-level protocol issues on top of the PPP link. For example, at this stage the IP Control Protocol (IPCP) can assign dynamic addresses to dial-in users. Thus, after three stages, a complete PPP link is established.
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