MTV Networks (NYSE: VIA) is readying Tribes, an online ad network tied to its various cable channels, Mediaweek reports. Tribes will pull in outside sites to establish ad sales and content syndication for MTV, VH1, Spike TV and CMT over the next several weeks. At some point after the new year, Comedy Central will get the Tribes treatment as well. Tribes is modeled on the ParentsConnect ad net, which MTVN’s Nickelodeon set up in February, with less than a dozen blogs and sites related to children’s entertainment. The company tells Mediaweek that ParentsConnect now has 46 sites, with more to come. At launch, Tribes is connected with Echo, which is comprised of several fan sites focusing on particular artists like Alicia Keys and Kanye West.

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—Not looking for the long tail: Heather Hopkins, a former exec at Publicis Groupe’s Digitas who heads Tribes as SVP and GM, tells Mediaweek that there is one main difference between the ParentsConnect and Tribes models: ParentsConnect’s small-mid-size sites are more long tail, Hopkins says, while Tribes hopes to group together sites around marquee names that draw big audiences. Eventually, the company hopes that most of the networks Tribes forms around the individual channels will end up three-five times larger than the foundation sites like MTV.com, which claims 8.7 million monthly uniques, and VH1.com, which draws 4.6 million, according to comScore.

—Mostly about advertising, less about content: While MTVN eventually plans to share some of its content with its partner Tribes sites, the relationships will involve advertising first and foremost. In the meantime, the company has had to overcome continued skepticism regarding the role of ad nets on the part of some major brands. In particular, the question of whether it would resemble a remnant ad net—which tends to stress wide reach for the lowest ad spend—versus verticals like Tribes, which is stressing narrowly targeted demos. In the case of Tribes, MTVN was able to convince Pepsi to give it a shot. John Vail, Pepsi’s director of interactive marketing, tells Mediaweek, “As a company, we’ve never been very active with ad networks. We were never about tonnage.” Still, don’t expect a major shift to online ads, as Vail adds that the company plans to use Tribes when it needs to meet a particular demand for “immediacy and relevancy” as opposed to the heavy lifting of general brand building.