The Design Of ADSL Access Router's Boot Module And NAT Protocol Module

In order to enhance our capability of product development and to get the better profit,we kept on developing on embedded system and internet technology. The ADSL internetrouter is one of the successful products which can bring us the profit, and the author of thispaper is one of members of project.Embedded systems are the special computer based on special application. Embeddedsystems are widely used in many fields: manufacture, process control, communication,instrument, automobile, marine vehicle, aviation, military equipment, and consumer product.Embedded systems are widely used in many fields: manufacture, process control,communication, instrument, automobile, vehicle, aviation, military equipment, and consumerproduct. A typical embedded application is the integration of hardware design centered on amicroprocessor or microcontroller and software development based on embedded real-timeoperating system.ADSL is a form of Digital Subscriber Line (DSL) Internet service. ADSL providesgreater bandwidth for downloads as well as upload speeds and it can provide 8Mbps fordownloads and 1Mbps for uploads. ADSL is the most common form of DSL used in homenetworking. ADSL is designed to support the typical home user who frequently downloadslarge amounts of data from Web sites. ADSL works by allocating a majority of the availablephone line frequencies for communication of downstream traffic.VxWorks, which is developed by the WindRiver company, is the most widely usedembedded real-time operating system now. Our ADSL product use the Intel IXDP425 chipand it is based on the VxWorks system, it supports the following network protocol: IP staticrouter, TFTP, FTP, Telnet, PPPOE, DHCP Server, DHCP Client, NAT.Vxworks is specific designed for the application of embedded system, it includes theBSP(Board Support Package) and operating kernel and user selected component andISR(interrupt service routine) . The main design's aim of the BSP module is to make the highoperating system independent from the low level hardware. The operating system is runningon the virtual platform, all the hardware code is included in the BSP package. It includes:1 .the hardware initializtion code when system power on . 2. the device driver of thehardware module in system .After system power on, the BSP start the initialization of CPU and other hardwares insystem . At last, the OS starts and then the multi-task environment is ready for work. Themain work of this paper discuss the BSP module. In oder to make it more efficient , wedivide BSP into 3 modules .They work together to complete the startup of the systemNAT lets organizations hide their internal IP addresses and provides a means forconnecting many more computers over TCP/IP. Because every computer which wants toaccesse the Internet needs its own IP address. An organization or a site within an organizationthat uses NAT can use almost any IP address internally for any purpose, with the exception ofa few IP address ranges that are reserved for internal network use. Unlike machines on yourinternal network that can use just about any IP address, machines that connect to the Internetmust use allocated (i.e., registered) IP addresses. However, you can use a NAT gateway toconnect any machine on your internal network to the Internet. The gateway will communicatewith the outside world on the internal machine's behalf and forward responses from theInternet to the originating machine on your internal network..The paper is based on the experiences in the project of ASDL router. Here the authordescribes the following points:According the author's work experiences and the project plan, this paper discusses thearchitecture of the whole project including the software and hardware and analysis abouthow to create a successful network product using embedded operation system likeVxWorks. For further understanding, the author explains the VxWorks kernel andnetwork interface in this paper.Since the project of ADSL router has it own hardware platform, it need a special BSPsupport. The author provides detail software design and the final solution with the helpof Vxworks BSP theory.As we all know, when updating the product software by network, the risk of networktrouble would make the product software system crash and can't reboot. In this paper, theauthor shows a good solution to resolve this known issue. This solution can make thesoftware system more stable and no crash even if the network has some troubles.The final focus of this paper is NAT protocol. Based on understanding the RFC3022protocol, the author explains the two different mode of NAT: Basic NAT and NAPT andhow to implement these two modes in the ADSL router product.At the last of this paper, I conclude the development of this project and its successfulexperience and the points that still need more attention. Wish these experience can benefit thedevelopment work of the simliar project.