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INTRODUCTION

EWT is the marriage of embedded systems and

the World Wide Web.

Embedded systems, in contrast to general

purpose computers such as a desktop, contain

processors, software, input sensors and output

actuators all of which are dedicated to the

control of a specific device.

EWT was developed during the late summer by

members of NASA Lewis Research Center, Flight

Software Engineering Branch of the Engineering

Design and Analysis Division of the Engineering and

Technical Services Directorate.

It was modified in 2002.

What is Embedded Technology ?

Embedded technology is software or hardware that is

hidden—embedded—in a large device or system.

It typically refers to a fixed function device, as

compared with a PC, which runs general-purpose

applications.

An early example of embedded technology is the

engine control unit in a car, which measures what

settings to give the engine.

INTRODUCTION TO THE EMBEDDED WEB SERVER

Embedded Web Server Technology is most evolving technology forInternet Devices. There are many application areas including internet devices,telecommunication devices, measuring instruments and lots ofconsumer electronics.

Emerging Web technologies for embedded applications

Design Issues for Embedded Web Servers

Traditional Web servers are designed to serve static Webpages from high-end workstations with plentiful CPU and memoryresources. Embedded Web servers have different requirements forwhich traditional technologies are unsuitable.

Protocol Considerations

Embedded Software Considerations

There are two primary actors when communicating over

the web, the server and the client. For right now think of

the server and the client as two desktop computers.

The server computer waits for the client computer to

initiate communication and then the client computer makes

a request for information.

If the server computer understands the request it replies

with a response.

If the server computer does not understand the request it

replies back to the client computer with an error. This

pattern is called the client-server.

Figure. Client-server model between two computers

To transfer information in this request-response manner both

the web service and the web browser must talk the same

language. That language is called Hypertext Transfer Protocol

or HTTP. HTTP is built on other standard protocols such as

TCP/IP.

HOW THE WEB WORKS The server boots up, when it is ready to starts the web service

program.

A user on the client machine opens up a web browser.

At this point both the web browser and the web service

are running and idle.

The client types in a URL in the address bar, which is related to

the location of the server, such as http://www.ni.com.

The server sees the request and replies back in HTTP with some

type of content, like a picture of a cat.

The client receives the response and since it is a web browser it

renders the cat picture so that the client sees a picture of a cat.

The embedded Web system works on the same principle

as that traditional Web request-response systems.

Web pages from the embedded system (server) are transmitted to

the Web browser (client) , which implements the user interface

(Presentation layer).

Web-enabled devices use the HTTP (Hyper Text Transfer

Protocol) standard protocol to transmit Web pages from the embedded

system to the Web browser , and to transmit HTML (Hyper Text

Markup Languages) form the data from the browser back to the

device.

The HTTP protocol engine takes the request from the Web browser

and sends it on the TCP/IP. The HTTP protocol Engine parses the

request and sends it to the embedded application for processing.

After producing the results , the embedded application generates

the HTML code and feeds it to the HTTP Engine , which sends it back

to the client using TCP/IP.

What is XML ? Extensible markup language (XML) is a structure for

text so that information can be easily stored and

transmitted through a web service.

Although the L in XML stands for language , but it is

not a programming language. XML is a popular content

choice because it is human readable, and translates easily

to other programming languages.

What is HTML? Hypertext markup language (HTML) is a language

used to describe a webpage.

When a web browser receives content that is HTML it

will try to render the content into a web page. Similar to

XML, HTML is made up of tags, but unlike XML,

HTML defines what types of tags are acceptable.

APPLICATIONS OF EWT

Space Communication

Biotechnology

Technology transfer and protocol

Education

Web technology in embedded applications has distinct advantages

over legacy and custom communication mechanisms due to the

ubiquity, scalability and security.

The amount of knowledge and skills needed to create a web

application may be large.

Hopefully this article helps the understanding of basic concepts and

how they apply to embedded applications.

Once all the pieces are integrated with each other, the

application becomes a functioning Web server that can be accessed

via serial or Ethernet connection. Using this New drivers were also

developed to interface the Net186 board to the parallel port cable of

the camera and to the serial port of the servo control.

CONCLUSION

[1] Han XiaoTao,Yin XiangGen, Zhang Zhe, LI Wei, ” Review of embedded

web server technology and its application in power system” [J] Power

System Technology 2003,(5): 58-62

[2] LI Yong,” Application and realization of CGI in embedded WEB

server”[J].Microcomputer Information, 2008,(30):110- 111.

[3] Li ShuiYang,HanTao, ”Application of embedded WEB server

technology” [J]. Journal of higher correspondence education(natural

sciences) 2003, (6)Vol. 16 No. 3: 47-50.

[4] Wan JiaFu, Zhang WenFei,Zhang Zhan Song ,“Principles and

applications of network monitoring system” [M].China Machine

Press,2003:178-289.

[5] Huang BuY, Zheng AnPing, Liu GuoMei , “Web technology implement

based onμCLinux”[J].Electronic Design & Application,2003,12:87-90.

REFERENCES