Cisco Systems ( CSCO), the networking giant with a reputation for niche acquisitions, agreed to buy privately held SyPixx Networks for about $51 million in cash and options. SyPixx, of Waterbury, Conn., offers video-surveillance software and hardware that enables existing analog video-surveillance systems to operate as part of an open Internet protocol network. Cisco said Tuesday it will now be possible for customers to continue using their existing surveillance systems and integrate them into an overall physical security program, while enhancing the safety of people and the protection of assets. The acquisition will likely close in Cisco's fiscal third quarter. Shares of Cisco were off 21 cents at $20.84.