The number of banners (images) is unlimited but it should be greater than 2. The number of image sources exceeds the number of images by one.
During a certain period of time one of the "employed" image sources will be replaced with an "unemployed" one through a fading effect. Because all images are the anchors their "href" property (link) is simultaneously replaced. Any one image cannot be replaced repeatedly within 2 consecutive cycles.
The speed of the cycle of transformation can be easily adjusted. A fading effect is available in IE only.