Comcast's "On Demand Online" trial - the countrywide test of an online-video subscription offering - has been signed in for by as many as 17 TV networks, including broadcaster CBS Corp.

While the financial details of the agreement remained undisclosed, the signing in of the companies clearly indicates that they are seeking additional revenue streams due to the ongoing advertising slump.

The Comcast experiment will offer a Web authentication system, which would require nearly 5,000 Comcast customers in markets across the country to authenticate their cable-TV subscription, to get access to programming online at Comcast's Fancast. com and Comcast. net sites, without any additional charges involved.

As per the framework, jointly worked out by Comcast and Time Warner, programming from cable networks would be put online, with the aim of satisfying consumer demand; alongside requiring customers to subscribe to a TV service, for avoiding any erosion in the revenue base of TV networks.

With the participation of bigwigs like CBS, the Comcast trial reflects the willingness of TV networks to work more closely with distributors, at a time when ad markets are suffering amid recession and Web players like Google are stealing market share.

Talking about the trial, Matt Bond, Comcast's Executive VP of content acquisition, said: "Today's announcement highlights the industry's growing interest to bring long-form content to consumers via a secure and easy-to-use online platform."