The Dublin-based provider of software for telecoms companies has raised funding from investors led by Japanese IT business NS Solutions.

Dublin-based Openet, which provides transaction management software to network operators such as Vodafone, BT and AT&T, has raised US$21 million (£13.5 million) in a Series D fundraising.

The round, which includes $16 million in equity funds and $5 million in long-term debt, brings the total amount raised by Openet over four funding rounds to $55 million.

Japanese IT company NS Solutions, a subsidiary of Nippon Steel, led the latest funding round. Existing investors also participated, including London-based venture capitalist Balderton Capital, which has backed Openet since 1999 and participated in all four rounds, as well as New York investor Cross Atlantic and venture debt provider Kreos Capital.

As part of the deal, Margaret Rice-Jones is joining Openet’s board. She is the former CEO of network management specialist Aircom International and also sits on the boards of NewBay, Psion, Abacus Polar and Trivanti.

Barry Maloney, a partner at Balderton, has served on Openet’s board since 2001.

Openet’s software allows telecoms operators to see how their customers are using services and charge according to usage. It is used by 80 customers in 28 countries.