webcams as an example for Client/Server in the internet


	webcams as an example for Client/Server in the internet Unique Identifier: 20000901E Author: Frank Petersen Address: Fachhochschule Hamburg, Fachbereich Elektrotechnik und Informatik, Berliner Tor 3, D-20099 Hamburg, Germany. Abstract: A webcamsoftware serves to capture images from a „Video for Windows“ camera or „capture card“ connected to a PC and to make those images available on the World Wide Web (web) on a web page. The webcam continues to capture images over time and to refresh the image. A web page usually contains images which have been manually uploaded to the Web server. A software can refresh the image on the Web server with images captured directly from the capture hardware. These new images can be uploaded to the web over the Internet using FTP. This upload should happen periodically. There are different technologies to transfer new imagedata periodically to the browser (Client): Server Push and Client Pull. Server Push is a technology pioneered by Netscape and implemented natively in the Netscape Navigator browser. When a browser accesses a Web page to obtain an image, the image is returned to the browser with a header which contains information about the content of the image. This header is in a format called MIME and is understood by all browsers. The MIME information allows the browser to interpret the format and content of the data. Server Push is an extension to the MIME format information. Instead of a single image being delivered to the browser, the MIME header informs the browser that it should expect a series of images to be received until an end-marker is located in the data delivered from the Web server. Unfortunately, only Netscape support Server Push natively. Image Pull is a technology to request periodically new imagedata from the server. Image Pull provides streaming video without requiring a Java Applet. Another possibility to provide streaming video is to use a Java Applet instead. The Internet Explorer and Netscape supports Java. With Java Applets Server Push and Image Pull are possible. The easiest way to implement webcamfunctionality is the usage of existing webcamsoftware, as i.e. WebCam32 and the Image Pull method.