2. 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.
3. 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.
4. 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.
5. INTRODUCTION
TO THE EMBEDDED WEB SERVER
Embedded Web Server Technology is most evolving technology for
Internet Devices.
There are many application areas including internet devices,
telecommunication devices, measuring instruments and lots of
consumer electronics.
Emerging Web technologies for embedded applications
Design Issues for Embedded Web Servers
Traditional Web servers are designed to serve static Web
pages from high-end workstations with plentiful CPU and memory
resources. Embedded Web servers have different requirements for
which traditional technologies are unsuitable.
Protocol Considerations
Embedded Software Considerations
6. 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.
7. 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.
8. 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.
9. The embedded Web system works on the same principle
as that traditional Web request-response systems.
10. 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.
11. 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.
12. 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.
14. 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
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[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.
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