Screenshot by Casey Newton/CNET

LAS VEGAS--A new front opened Monday in the fight to own place-shifting devices when Sling Media, a subsidiary of EchoStar, filed a lawsuit against two of its rivals that accuses them of patent infringement.

Sling, maker of the Slingbox devices that allows users to watch and control their home television from anywhere, filed suit against competitors Belkin International and Monsoon Multimedia. Both are California companies that make devices that compete with the Slingbox at lower prices -- Belkin's @TV and Monsoon's Vulkano.

The announcement comes on the same day Dish Network, a key technology partner of EchoStar, announced an expanded version of its Hopper whole-home DVR that integrates Slingbox into the device for the first time. The integration allows customers to move programs onto the iPad and access Dish programming remotely though the Web or mobile devices.

It suggests that Sling, which has been popular among critics but has yet to achieve widespread adoption, has decided to take a more aggressive tact in thwarting rivals and building its customer base. And it comes during a CES when executives at media and entertainment companies are telling attendees that increasingly, customers expect to be able to watch TV and movies wherever they are, on whatever device they have at hand.

For years, critics said the Slingbox was irrelevant in a world where cable programmers and broadcasters made all their shows available online. But that hasn't completely happened. Cable operators have promised to eventually roll out their "TV Everywhere" initiatives. But that's largely been a no-show -- and while the world waits, allowing users to watch their cable shows online is becoming an increasingly large opportunity for Dish.

The lawsuit, filed in U.S. District Court for the Northern District of California, alleges that the companies violated five Slingbox patents, including U.S. Patent 7,725,912, "Method for Implementing a Remote Display System with Transcoding"; U.S Patent 7,877,776, "Personal Media Broadcasting System"; U.S. Patent 8,051,454, "Personal Media Broadcasting System with Output Buffer"; U.S Patent 8,060,909, "Personal Media Broadcasting System"; and U.S Patent 8,266,657, "Method for Effectively Implementing a Multi-Room Television System."

A Belkin spokesperson declined to comment. Monsoon did not respond to a request for comment. We will update this story when we have heard from them.

A Slingbox spokesman said the technologies had been developed by the company in-house and are essential to the operation of its devices. He declined to comment on the timing of the suit, which came as CES 2013 is in full swing.

Last summer, Belkin put Slingbox in its crosshairs when it announced it would release @TV, a place-shifting device similar to Slingbox. Both devices enable cable subscribers to watch their favorite channels wherever they can connect to the Internet. EchoStar, which acquired Sling Media in 2007, also saw Belkin undercut Slingbox on price. Slingboxes are available at Best Buy for $179.99 (the Pro HD model goes for $299). Belkin was selling @TV for $149.99.