US networking giant Cisco appealed on Wednesday against the European Commission's approval of Microsoft's $8.5 billion takeover of Internet voice and video leader Skype.

Cisco senior vice president Marthin De Beer said in a blog post that Cisco does not oppose the merger but the Commission should have required greater interoperability between video-calling systems.

Cisco is a leading provider of video conferencing systems and a source close to the company told the TechCrunch technology blog that the appeal was filed after Cisco and Microsoft failed to reach an agreement on common standards.

Messagenet, a European Internet communications service provider, has joined Cisco in the appeal.

"This appeal is about one thing only: securing standards-based interoperability in the video calling space," De Beer said. "Our goal is to make video-calling as easy and seamless as email is today.

"Cisco does not oppose the merger, but believes the European Commission should have placed conditions that would ensure greater standards-based interoperability," De Beer said.

This was necessary, the Cisco executive said, "to avoid any one company from being able to seek to control the future of video communications.

"Making a video-to-video call should be as easy as dialing a phone number," he said. "Today, however, you can't make seamless video calls from one platform to another, much to the frustration of consumers and business users alike.

"Cisco believes that the right approach for the industry is to rally around open standards," he said.

"For the sake of customers, the industry recognizes the need for ubiquitous unified communications interoperability, particularly between Microsoft/Skype and Cisco products, as well as products from other unified communications innovators," De Beer said.

The European Commission approved Microsoft's takeover of Skype in October and the deal gained US approval in June.

Microsoft said it did not expected the European Commission to go back on its decision.

"The European Commission conducted a thorough investigation of the acquisition, in which Cisco actively participated, and approved the deal in a 36-page decision without any conditions," a Microsoft spokesman said.

"We're confident the Commission's decision will stand up on appeal," the spokesman said.

Cisco was reportedly among the buyers interested in Skype, which was founded in 2003 and acquired by online auction giant eBay in September 2005.

Skype was sold to an investment group led by Silver Lake in November 2009 in a deal that valued the company at $2.75 billion, and was bought by Microsoft in May.

Skype users can make low-cost or free phone calls over the Internet using their computers or smartphones. Skype bypasses the standard telephone network by channeling voice and video calls over the Web.