Nortel Networks has hung up on the telecom sector. Once one of the largest makers of telecommunications equipment in North America, it filed for bankruptcy protection in 2009 and is in the process of liquidating its assets. The company made core network switching, wireless, and optical systems for network operators. Its wireline and enterprise network equipment included systems for digital voice and data switching, routing, and call center communications. Wireless products included cellular base stations and controllers. The company also made such long-haul fiber-optic products as multiplexers. Nortel is currently focused on selling off its remaining businesses and intellectual property and winding down all operations. Today, Nortel's Metro Ethernet Networks segment provides carrier Ethernet switching, optical networking, and multi-service switching products.