Logo of Openet, Irish transaction software developer that raised an additional $21 million in venture capital in June 2012. Openet

Openet, one of Ireland's flourishing software developers, said it raised an additional $21 million from investors in Japan, Europe and the U.S., bringing the cumulative total raised in 13 years to $55 million.

We could have raised either a very small amount of money or a very large amount, said CEO Niall Norton, 45, in an interview. This was about right. He said the European financial crisis didn't hamper the round.

Dublin-based Openet specializes in software for telecommunications network providers including Verizon Communications (NYSE: VZ), AT&T Inc. (NYSE: T), the No. 1 telecommunications carrier, and the Netherlands unit of Vodafone Group (Nasdaq: VOD), although this year nearly 20 percent of revenue should come from other sources.

Openet, which employs 850 in Ireland, the U.S. and Malaysia, could file for a future initial public offering, Norton said, but has no immediate plans for it.

The latest investors include NS Solutions of Japan, part of Nippon Steel (Tokyo: 5401); Balderton Capital of the UK, Cross Atlantic Capital Partners of Radnor, Pa., and Kreos Capital of the UK.