Juniper, the biggest rival to giant Cisco Systems in the router business, will acquire Unisphere for US$375m (£257m) and 36.5 million shares, according to a statement from the companies.
Based on Juniper's closing stock price of $9.85 on Friday, the deal will be worth about $740m (£508m), the statement said. The acquisition is subject to regulatory approvals and is expected to close in the autumn.
Unisphere makes routers, gateway devices and other equipment and software for networks based on IP.
As part of the agreement, Siemens will sell Juniper's routers and other carrier equipment through its sales and system integration operations around the world. Juniper's equipment will help Siemens create next-generation networks that can carry voice and video as well as data over IP networks, the company said.
Juniper plans to continue enhancing its own Junos software as well as Unisphere's software.
Juniper's partnership with Ericsson is unaffected by the new relationship.
Unisphere's lineup would bring in features such as sophisticated service management software and MPLS VPN (Multiprotocol Label Switching virtual private network) initiation.