15-11-2012, 12:58 PM
Embedded Web Technology
1Embedded Web.doc (Size: 345.5 KB / Downloads: 73)
ABSTRACT
Embedded Web Technology (EWT) is regarded as the ‘marriage' of Web technologies with embedded systems. In other words, the software developed for embedded systems is applied by making use of the Internet.
Embedded technology has been around for a long time and its use has gradually expanded into the PC market. Speed, accuracy, reliability were the reasons why embedded technology entered computers. With an great market size of billions in the next coming years, the future is embedded. Embedded systems contain processors, software, input sensors and output actuators, which work as the controls of a device and are subject to constraints.
These Embedded systems may not have disk drives, keyboards, display devices and are typically restricted in terms of power, memory, GUIs and debugging interfaces.The central building blocks are microcontrollers, i.e. microprocessors integrated with memory units and specific peripherals for the observation and control of these embedded systems.On the other hand, Web technologies employ client-server models.
Introduction of Embedded Web Technology
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). In other cases , the the embedded system dynamically generates the pages to convey the current state of the device to the user at the centralized location. These end users can also use the Web browser to send the information to the embedded system for the configuration and control ofd the device.
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 devices require a network interface such as Ethernet ,TCP/IP software , embedded Web server software , and the Web pages (both static and generated) that make up the device- specific GUI.
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.
Functional principle of a Web Server
Simplified a Web server can be imagined like a special kind of a file server. Picture 2.A
shows an overview. The Web server receives a HTTP GET-request from the Web browser.
By this request, a specific file is required as answer (see step 1 into picture 2.A). After that,
the Web server tries to get access on the file system of the requested computer. Then it
attempts to find the desired file (step 2). After the successful search the Web server read the
entire file (step 3) and transmit it as an answer (HTTP response comprising of header and
content object) to the Web browser (step 4). If the Web server cannot find the appropriate file
in the file system, an error message (HTTP response which only contains the header) is
simply be send as response to the client.
Web Server running under Linux
Once spoken about Web servers in connection with Linux most people immediately think of
Apache. After investigations of the Netcraft Survey this program is the mostly used Web
server worldwide. Apache is an enhancement of the legendary NCSA server. The name
Apache itself has nothing to do with Red Indians. It is a construct from "A Patchy Server"
because the first version was put together from different code and patch files. Moreover there
are numerous other Web servers - even for Linux. Most of this are standing under the GPL
(like Apache) and can be used license free. A very extensive overview you can find at
"http://directory.google". Every Web server has his advantages and disadvantages. Some
are developed for specific functions and have very special qualities. Other distinguishes at
best through their reaction rate at many simultaneous requests, as well as the variety of their
configuration settings. Others are designed to need minimal resources and offer very small
setting possibilities, as well as only one connection to a client