Shanghai Unicom, a subsidiary of China Unicom, and NSN (Nokia Siemens Networks) have sealed a deal for network maintenance in Shanghai, according to a May 10, 2011 press release by NSN. As per the five-year deal, field maintenance services to be offered by NSN will cover base stations, transmission networks, and fixed line networks, starting from May this year. It is the second management services contract signed between China Unicom and NSN, according to the same source. China Unicom's another subsidiary Anhui Unicom awarded a field maintenance contract to NSN in October 2010.