The Research And The Implementation Of Physical Layer Of The Embedded ADSL Gateway

ADSL (Asymmetric Digital Subscriber Line) is a broadband access technology capable of delivering large bandwidth over existing copper telephone line infrastructure. Asymmetric Digital Subscriber Line can supply the necessary bandwidth for applications such as fast access to the Internet, video conferencing, interactive multimedia, and Videoon-Demand. This technology is designed to solve the most severe bottleneck in the data access network between the Central Office and the customer, or end-user. ADSL is a new modem technology (the bandwidth is from 25.875K to l.lMhz) that converts existing copper telephone lines into access paths for multimedia and high speed data communications, and maintains the regular telephone voice services. ADSL provides data rates that expand the best existing access capacity (ISDN) by a factor of 60 or more, and the best existing common analog access capacity (V.34 modems) by a factor of 300, without requiring any new cabling. ADSL can practically transform the existingpublic information network from one limited to voice, text and low resolution graphics to a powerful, ubiquitous system capable of carrying multimedia, including full motion video, to everyone's home. With the development of VLSI and DSP technology, DSL is getting more and more mature. ADSL implement A/D, D/A conversion, DMT&TCM and some necessary coding, by this way, ADSL can achieve high efficiency of bandwidth and guarantees credibility We use Itex ADSL Development Tool (IADT) to simulate the Central Office, by this way, we can observe the performance of the ADSL, including the overall performance monitor and subchannel performance monitor, we also present the arithmetic of every modules of the ADSL. As to accessing to the backbone, ATM is proved to be scalable and fast, also because PPP is used to be a solution to user's authentication and charging, we adopt the PPP over ATM solution. Generally the protocol stack of ADSL accessing network can be described as TCP/IP over PPP over ATM. ADSL isgenerally apply to the SOHO accessing to Internet, we present the design of the ADSL SOHO gateway, including the hardware and software implementation.Both hardware and software are contracted designed, we adopted ElanSC520 as the CPU, plus 2M flash and 16M SDRAM, and it's a typical example of embedded system. We adopted ITEX'S Apollo 3 PCI solution as the uplink end, REALTEK 8029 and WLAN at the other end. We adopted linux as the gateway operating system and integrated some application with it to implement DHCP, SNMFJ and Firewall etc.