It's been an ongoing debate for much of the last 14 years -- Cisco or Juniper? Increasingly, that argument will hinge on which router manufacturer has the more compelling unified data center fabric architecture: Cisco's Unified Computing System or Juniper's single-layer Stratus. The Battle Between JUNOS and IOS The argument began in 1996 with Juniper's founding; until then, Cisco had ruled the router roost in both the enterprise and service provider markets since its founding in 1984. But with the growing importance of the Internet, venture capitalists and unhappy Cisco customers sunk money into the idea of forming a start-up to build a better mousetrap, specifically for service providers. Juniper's first year was nurtured with early investments from the Anschutz family (Qwest's majority stakeholder), AT&T, Ericsson, Lucent, Nortel, Siemens/Newbridge Networks, 3Com and UUNET. IBM agreed to develop custom ASICs for Juniper's Internet routers, the first of which was the M40. With all the heavyweight backing, Juniper became and is still Cisco's most formidable challenger in service provider routing. The company gradually attained a roughly 30% share of the $8 billion market, virtually all at Cisco's expense, and has been the technological darling of some bitheads over the past decade for the purity – or purpose-built specialty – of its silicon and software. This remains Juniper's chief differentiator from Cisco. Cisco was viewed as a packager of enterprise-class products that were being deployed in more demanding service provider requirements. Cisco's dominance and ubiquity in routing made many of its customers hungry for an alternative. Cisco isn't standing still. It's been re-energized by the emergence of Juniper and the recent gains of Alcatel-Lucent in service provider edge routing. In 2009, Alcatel-Lucent leapfrogged Juniper's nine-year hold on the No. 2 market share position in the service provider edge, according to Dell'Oro Group. And Cisco still holds the lion's share of the enterprise and service provider router market, with a customer base that's mostly loyal to its incumbency. But it is Cisco and Juniper that try to leapfrog each other technologically in the service provider core and edge. Right now, the multi-chassis core race pits Cisco's Carrier Routing System against Juniper's T Series for tens – even hundreds -- of terabits supremacy. Juniper is taking the battle to enterprise data centers and cloud computing environments. Emboldened by its success in carrier routing, Juniper unveiled enterprise Ethernet switches two years ago in an attempt to become a credible alternative to Cisco's dominance in that market, too. The company believes it can carve a niche in the elite networking arenas of financial trading, high-performance computing and other demanding enterprise environments just like it did in service provider routing. In the data center, both companies are surrounding themselves with high-profile partners to help push their competing visions: Cisco with EMC and VMware, and Juniper with IBM. At stake, just as in service provider routing, is a multibillion dollar opportunity – $85 billion in private clouds by 2015, according to Cisco – to become the primary supplier of next-generation data centers, further entrench new and existing customers, and lock its rival out of lucrative, big ticket accounts.