For a CEO who just lost his job, Frank Plastina was exceptionally upbeat Wednesday.

Plastina abruptly resigned Tuesday from Morrisville-based Tekelec after steering the telecommunications software company through five years of industry change. Since the recession hit, pressure had been building for Plastina to show signs of improvement at the 1,250-employee global company. Tekelec’s stock had lost 23 percent of its value in the past year alone, and technology product orders had declined two years running.

On Wednesday, all of that was somebody else’s problem. The telecom industry veteran, 48, walked away with a $2.5 million severance package, health care coverage for the next two years and a hankering to reinvent himself yet again as mister fix-it.

“I’m not sorry at all,” Plastina said by phone from hisCary home. “Now was a good time to hand it off. I’d rather do something that’s personally fulfilling at this stage.”

Plastina and Tekelec officials agree that the company must boost sales of next-generation telecommunications software. Tekelec’s roughly 300 customers, including Verizon Wireless and AT&T, are upgrading networks to handle high-speed downloads of movies, videos and other heavy-duty data that are increasingly being pinged around the Internet by smart phones and wireless tablets.

That means changes are likely at the company, which employs 675 people at its Morrisville headquarters. Possibilities include selling off units with less growth potential, or shifting employees to new functions, said analyst Blair King at Avondale Partners in Nashville.

“I wouldn’t be surprised to see some reshuffling at Tekelec this year with more focus on the growth components of their business,” King said. “In reality you’ve got a business in a pretty sexy spot in the industry that’s not been valued properly.”

Plastina is a known quantity among the Triangle’s technology community. He’s a current board member of Cree, the Durham lighting maker. He spent much of his career in management and executive positions at Nortel Networks in Research Triangle Park, where he had worked in the mid-1990s after moving here from his native Canada.

Plastina joined Tekelec in 2006 after several years of cross-country commuting to work for a Manhattan private equity firm and running a Silicon Valley Wi-Fi and wireless broadband startup.

Plastina said his departure from Tekelec was a mutual decision, a topic that had been broached between him and the board of directors on previous occasions. On Monday all agreed now was a good time. The company will start looking for a permanent replacement. Krish Prabhu, a member of its board of directors since May 2008, will be interim CEO.

Investors reacted positively to the news, pushing up Tekelec’s stock’s value over 10 percent, to $13.28 a share.

Tekelec got its start as a maker of telecommunications equipment and hardware. Under Plastina it shifted its focus to telecom software that handles and sorts data and call traffic.

But the transition to next-gen technology was not moving as fast as had been hoped, raising questions about the company’s strategy and execution. Product orders overall declined about 10 percent in 2010 and again in 2009.

“That’s the question every investor asks me, every time: What’s the date, time and place when the growth of next-generation products will exceed the decline in [legacy] products?” said Greg Rush, Tekelec’s chief financial officer. “We’ve had a two-year orders decline, and people are trying to understand [where we're headed].”

As part of the resignation announcement, Tekelec said it will fall short of its financial expectations for 2010. That news comes after the company had previously lowered its guidance twice in the past year.

The major reason Tekelec fell short, Rush said, is that the government of India has delayed a large product order for security reasons.

He also said the company’s fourth quarter was its second-best ever in product orders, a sign that prospects are improving. Orders are the best indicator of the company’s future performance.

In his farewell to employees on Wednesday, Plastina said he credited them for the company’s accomplishments and expressed confidence in the company’s future success. Asked later why he wasn’t the one to take the company to the next level, Plastina said he was eager for a change.

“Five years is a long time these days for a CEO,” Plastina said. “It’s time to pass the baton and move on to something else.”

For him, that could be philanthropic work. He has been active on numerous local corporate and nonprofit boards, including the N.C. Symphony and the Wake County Boys and Girls Club, but the round-the-clock demands of running a global technology company forced him to give up most of those positions.