4 Models Description - Image Description
The picture is composed of three main objects with interconnecting lines and features. The first object is a blue sphere in the upper right corner with the label "WWW." The sphere represents content available on the World Wide Web (or Web for short). To the left and center is a large white cloud which represents "cloud" computing. The cloud includes servers on the Web that provide accessibility services and features that would be run on servers out in the Web somewhere. The third main component is a rectangle across the bottom of the page labeled "Local Computer/Device". This represents the device that a person would have in front of them such as a desktop computer, a laptop or a small screen mobile device. The computer could be a personal computer or just a computer that a person runs into someplace.
There is a line labeled "1" that has an arrow on the end and runs from the Web content directly down to the user agent (browser) in the Local Computer. This represents Model 1, where a browser directly reads and processes Web content.
There is an arrow line labeled "2" that runs from the browser in the Local Computer up into the cloud, through a box labeled "Transcoding Services" and then back to the browser in the local computer. This represents Model 2, where a browser, content in the browser or the user sends content to a transcoding service that changes the content in some way and then sends it back to the browser for display.
There is an arrow line labeled "3" that runs from the Web content in the upper right to the box labeled "transcoding services" in the cloud and then to the browser in the local computer. This represents Model 3 where all content is routed through a transcoding service in a proxy server that changes the content in some way before the user's browser ever receives it.
The final arrow line labeled "4" runs directly from the Web content to a browser that is located mostly in the cloud, but partially in the local computer. This represents Model 4 where the user agent or browser with special access features built in is run as a service in the cloud. Only the basic human interface parts (keyboard, mouse, display, sound) are run on the local computer. The Local Computer aspect could be a special program on the computer, but would usually run as an app within a browser on the local computer.