Financial details were not disclosed.
Ascend bills MultiVoice as an architecture for deploying "toll quality" voice and fax traffic over Internet Protocol and Frame Relay networks.
The firm said it uses scalable WAN networking technologies, new developments in voice compression, and quality of service mechanisms to provide bandwidth.
Under today's agreement, components of PSINet's PSIVoice suite of products will be built on Ascend's MultiVoice for the MAX solution.