India Broadband Forum

rupu1983

Video on demand(VOD) is the Broadband service for entertainment purpose; particularly it is video based entertainment on Broadband telecommunication. This service is design to provide the customer access to a large number of first run movies. The customer, by means of a set top box (STB), can access virtually any movie. The STB decode the digital signal into analog form and provide the menu and control functions to access the list of movie titles, request a movie title, and control the viewing (start, stop, pause).One can immediately observe that such service is quite expansive but near future it will not be expansive. For the viewer to have such control over an individual movie would require complex and expansive server, probably with multiple (perhaps several thousands) copies of popular films. For example, 90 min film digitally compressed at 4 mbps would require 90 * 60 s/min *4 *(10 to the power 6) =2.7 GB media storage and that mean total 270 terabyte (for 1000 titles and 100 copy of each title)
Because of the tremendous storage requirement and costly servers, perhaps at multiple locations a less costly alternative called near video on demand (NVOD) has been proposed. NVOD starts at individual film at regular intervals, perhaps 10 min. Instead of several thousand copies for first run, highly popular film, only six would be required at each server location. If the viewer need to leave the television set for few minutes, He/she would need to wait 10 min at the most to return the point at which film was stopped. The STB would automatically determine where to rejoin the film, that is, which of six transmissions too access.VOD and NVOD requires two way communication with the server provider. The video transmission is referred to downstream; the user control is called upstream. Bandwidth require substantially smaller in the upstream direction than the downstream direction. For this reason, such services are called asymmetric.

....................................Source—Books of Analog & Digital communication