Bethesda-based Opnet Technologies has agreed to be purchased for $1 billion pending regulatory approval, the firm announced Monday, making the application performance management firm the region’s latest high-ticket acquisition.

The buyer is Riverbed Technology, a San Francisco-based company that sells IT software and services. The firm plans to merge Opnet with an existing business unit called Cascade that provides network management services.

Riverbed will pay $43 per share in cash and stock for Opnet, according to the agreement, which equates to an equity value of $1 billion and an enterprise value of $921 million, the companies said.

The deal is expected to close by the end of the year.

Openet was founded in 1986 by brothers Alain and Marc Cohen as a ”tiny garage operation” that eventually went public 14 years later. For fiscal year 2012, the firm posted net income of $18.3 million on total revenue of $172.7 million.

Roughly half of the firm’s 700 employees are based at the Bethesda headquarters, and chief executive Marc Cohen said he hopes the acquisition will allow the company to grow its headcount here.

“We have plans to grow,” Marc Cohen said. “Riverbed and Opnet will continue to expand in this area, so there’s no plans to make any changes here in Bethesda.”

“We both plan to stay at the company,” added Alain Cohen, the chief technology officer. “We have prominent roles in the new company. We’ll continue to lead the vast majority of the people we currently do lead in our company so we’re very excited about the future.”

The 26-year march from start-up to buyout target has had its twists. The executives said when Openet first opened it helped to design communication and information technology networks. It has pivoted probably three or so times since then to keep pace with industry trends.

“It’s been a great journey,” Marc Cohen said. “We believe, however, that to take advantage of the window of opportunity that’s in front of us, which is going to be the next three to five years in the application performance space, it makes more sense to be part of a bigger platform.”

An earlier version of this story incorrectly reported when Opnet went public. It went public in the year 2000.

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