The wireless router is a network device based on GPRS/CDMA1X public mobile network platform that wirelessly accesses the Internet or VPDN. It can provide a mobile, low-cost TCP/IP-based data transmission channel.
Wireless routers can be widely used in finance, insurance, power, monitoring, transportation, weather, hydrological monitoring and other industries. Using a stable GPRS/CDMA1X wireless network, wireless routers can replace some wired Ethernet routers, HUBs, and wired MODEMs to enable wireless data transmission. Under the conditions covered by the public mobile network, the Ethernet interface was originally used, and various terminal equipments relying on the wired Ethernet communication system, such as PCs, IPCs, ATMs, POS machines, and network cameras, etc., can be easily passed. The wireless router accesses the GPRS/CDMA 1X network and utilizes the data services provided by the mobile internet for data communication.
Fig.1 Schematic diagram of the simulator operation
Compared with traditional wired network access, wireless router equipment has the following advantages:
·Wireless TCP/IP services can be provided quickly without being constrained by cables.
· With mobility, it can be installed on mobile carriers such as ships, trains, and cars.
Flexible and changeable, as needed.
Wireless Router Hardware Design
The wireless router is composed of a wireless communication module, an Ethernet interface, an embedded processor and a memory, and a power supply module. As shown in FIG. 1, one end of the wireless router is connected to a GPRS/CDMA 1X network through a wireless communication module, and the other end is connected to the Ethernet. The network interface is connected to network terminal devices such as PCs, network cameras, multimedia terminals, etc. The wireless router is equivalent to building a bridge between network terminal devices and the Internet. The wireless communication module partially completes the work of accessing the GPRS/CDMA 1X network, which is equivalent to a mobile modem that can dial-up the Internet.
The wireless router connects to the GPRS or CDMA1X mobile internet through the wireless communication module, and connects to the internal network device or the internal LAN through the Ethernet interface. Wireless routers have network routing capabilities that can forward data between two networks. The data sent by various terminal devices is received by the processor through the Ethernet port. The processor processes the data and sends it to the wireless communication module through the serial port 1, which forwards it to the GPRS or CDMA network. In the same way, the reverse data from the wireless network is eventually sent back to the network terminal equipment through the opposite path.
Wireless router hardware includes embedded processors, memory, wireless communication modules, interfaces, and power supplies, as shown in Figure 2.
Figure 2 Wireless Router Hardware Design Block Diagram
processorThe wireless router's embedded processor uses ARM processor S3C4510B, core is ARM7TDMI, and the main frequency is 50MHz. It provides two UART serial ports, one I2C bus controller, one real-time clock and one 10/100Mbps Ethernet. Controller.
MemoryThe FLASH memory is a 1M&TImes; 16-bit data width HY29LV160, its capacity is 16M bits (2M bytes), and the operating voltage is 2.7V~3.6V.
SDRAM memory is a 16-bit data width HY57V641620, its capacity is 4 groups & TImes; 16M bits (8M bytes), operating voltage is 3.3V.
The I2C memory is a single AT24C01, which provides 128 bytes of EEPROM memory and can be used to store a small amount of data that needs to be saved when the system loses power.
Wireless communication moduleThe GPRS module Q2406B or CDMA1X module Q2358C produced by Wavecom is used. The embedded processor is connected to the wireless communication module through the serial port 1. The module communicates with the cell base station of the public mobile network through an external antenna to receive and send wireless data.
External InterfaceThe router has three external interfaces: an antenna interface of an SMA connector, 50 Ω impedance; an RJ45-seat 10M Ethernet interface connecting various network terminal devices; and a DB9 RS232 serial interface, which can be configured as a console interface. Used to set parameters and device operation monitoring. It can also be configured as a serial port data conversion interface for converting serial port data into network port data.
power supplyTaking into account the vehicle battery voltage is mostly +12V, in order to facilitate the connection of car cigarette lighter or car battery, wireless router power module uses DC power +12 input, output 4V, 2.8V, 3.3V, respectively, to the wireless communication module, S3C4510, FLASH and other digital circuits.
Wireless Router Software Design Operating System SoftwaremClinux is a fully-compliant GNU/GPL (General Public License) project and fully open code. It is a branch of standard Linux and is now supported by Lineo. It is specifically aimed at CPUs without MMUs and has done a lot of miniaturization work for embedded systems.
The wireless router's operating system software uses mClinux, which is an embedded operating system based on the Linux kernel open source code. Since the hardware circuit of the wireless router is specially designed for this application, mClinux cannot be used directly, so the part of the source code related to the hardware circuit in the mClinux operating system software is re-modified so that the mClinux operating system can operate normally on the wireless router circuit board. The main changes to mClinux are:
ARMS3C4510B and memory chip initialization program;
mClinux kernel bootloader;
Wireless router configuration files for various network applications;
· For the ARMS3C4510B processor, select the appropriate compiler tools and parameter options to recompile the entire operating system.
Wireless router supported network protocols
The network protocols supported by the wireless router are shown in Table 1.
Table 1 Wireless router supported network protocols
applicationThe network interface of the wireless router includes a wired Ethernet interface and a wireless dial-up Internet access interface. The role of the wireless router is to forward data between the two interfaces and provide a static routing function. The implementation code of the TCP/IP network protocol has been embedded in the mClinux operating system. By setting "IP forwarding" and "IP masquerading" in the kernel, the static routing function can be realized. Application software design mainly includes two network applications: PPP application and iptables application.
PPP applicationThe PPP application is used to dial into the GPRS/CDMA1X mobile network through the wireless communication module. The login process follows the PPP point-to-point communication protocol. The mClinux operating system code contains a program pppd that implements the PPP protocol, but it is necessary to modify some of the pppd source code configuration parameters, such as the dialing number, login user name, and login password, according to the requirements of the GPRS/CDMA1X mobile network communication. Get the required PPP application and dial up to log in to the mobile network.
Iptables applicationThe iptables package supports data processing package disguising and filtering functions, which are called netfilters. In the wireless router we use the "IP forwarding" and "IP masquerading" features.
"IP forwarding" function:
#echo1" /proc/sys/net/ipv4/ipforward
"IP Masquerade" function:
#iptables-t nat -A POSTROUTING -o ppp0 -j MASQUERADE
The working principle of "IP Masquerading" is: When the router dials up, it has two network interfaces, and they both have two IP addresses:
a. Dial-up network interface ppp0 is a dynamic legal public network IP address, assuming abcd;
b. Ethernet interface eth0 is a fixed private network IP address, assuming 192.168.1.1
If the Ethernet port is connected to a LAN 192.168.1.x, usually the devices in this LAN cannot access the public IP. The LAN terminal device (assuming its ip address is 192.168.1.22) sets the IP address of the wireless router's Ethernet interface 192.168.1.1 as the default gateway. When the wireless router receives a request packet from the LAN device to access the public network, it passes the above. The "IP Forwarding" command forwards it, and then overwrites it with the "IP Masquerade" command, replaces the source address 192.168.1.22 of the packet with its own legal IP address abcd, and replaces the source port number port1 with a The new port number port2, and the process is recorded.
When the wireless router receives the response packet from the Internet host, if the destination port number is the previously modified port number port2, the packet is reversed and the destination IP address (abcd) and destination port number of the response packet ( Port2) is replaced with the IP address 192.168.1.22 and port number port1 of the originally recorded LAN device and then sent to the LAN device.
Converting a private network address to a public network address is accomplished by a database stored on an iptable-based wireless router. The iptable software of the wireless router maintains this database, so it knows how to perform "reverse conversion", so the data returned from the public network can be sent to the source access device correctly.
Terminal device access to wireless network
The wireless router provides two interfaces for the terminal device, respectively Ethernet interface and wireless ppp interface. The routing software in the wireless router automatically forwards the data from the wired network device of the Ethernet port to the GPRS/CDMA network, or receives the data from the GPRS/CDMA network and forwards the data to the wired network device of the Ethernet port. This kind of wireless router's automatic forwarding capability provides the following three functions:
·Data forwarding of network terminal equipment
As long as the network terminal equipment is connected to the wireless router through the Ethernet port and the default gateway is set to the IP address of the wireless router, it can access the GPRS/CDMA network. There is no need to make any changes to the communication software of the terminal equipment itself.
Plug and play of network terminal equipment
The wireless router has a built-in DHCP server. As long as the terminal device is set to automatically obtain an IP address and connect to the wireless router through the Ethernet port, it can automatically obtain dynamic IP address, gateway address, subnet mask, DNS, and other network parameters through the DHCP protocol, and then can access the GPRS/ CDMA network. The communication software of the terminal equipment itself does not need to make any changes, and it is truly plug and play.
·Mobile network adaptation
The built-in software of the wireless router can automatically identify the type of wireless communication module configured in the router hardware, and then use different dialing parameters to log in to the GPRS or CDMA1X mobile network.
Figure 3 Device outline of wireless router
ConclusionWired network terminal equipment can use the existing GPRS/CDMA1X network to complete wireless network access through a wireless router without laying a network cable. CDMA1X wireless router equipment can be used as emergency communication means in highway monitoring, flood prevention command, mountain fire prevention, and geological disasters. In remote areas where islands, automobiles, Three Gorges cruises, trains, etc., are difficult to install communication lines or are uneconomical to build, using a GPRS/CDMA 1X wireless router to access the Internet or a dedicated VPDN is a quick and inexpensive solution. This equipment has been used in the Taihu Lake Basin Hydrological Data Monitoring System.
In short, within the coverage of GPRS/CDMA1X cellular network, wireless router equipment can provide wireless network communication services quickly and economically. The wireless router device implemented by the method provided herein has strong versatility and can operate with high efficiency.
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