At the same time, the enterprise was becoming a market for converged voice, video, and data, ushering in a completely new set of technology requirements -- and forcing Cisco to become proficient at handling the sort of traffic that has been the bread-and-butter of its 100-year-old telecommunications brethren.

"Markets develop in strange ways, acquisitions are needed to fill gaps, and sometimes integration work falls off the development priority list when compared to maintaining an existing customer base," says Mark Seery, vice president of switching and routing research at Ovum/RHK. "Are there times when departure from one software platform makes sense? Yes, there probably are, but they should be the exception rather than the rule."

Cisco late last year introduced the latest big change to IOS: A plan to allow third-party and customer-developed applications to access IOS services that were previously off limits. (Juniper aired similar plans for JUNOS around the same time.)

Juniper's approach
Juniper began business 12 years ago with a clean slate to develop an operating system for service-provider routers. Its routers and the JUNOS operating system that controlled them were "purpose built" for the service-provider market, a key differentiator for the company vis-à-vis Cisco and its enterprise-born IOS.

Since then, however, Juniper has broadened its target markets -- most notably into the enterprise -- and acquired several companies, including Unisphere in edge routing and NetScreen in enterprise VPNs. Despite its derisive rhetoric directed at multiple operating systems, Juniper acknowledges it's now facing some of the same challenges as Cisco.

"A lot of these products are the result of acquisitions," says RK Arnard, Juniper executive vice president of foundation technologies, referring to the NetScreen, Unisphere, and other inorganic gear in Juniper's portfolio.

"We have to be careful about an installed base, customer commitments, and continued delivery on products we acquire," Arnard says. "Our approach has been fairly deliberate and planned and scheduled in a systematic manner about incorporating and bringing technologies that come as a result of these acquisitions into JUNOS while at the same time, continuing to ship existing systems."

Juniper last month released JUNOS 9.0, 20 million lines of code that incorporates security features obtained from its NetScreen acquisition four years ago. Juniper rolls out a new release of JUNOS every quarter, each one a "superset" of its predecessor, Arnard says, while Cisco ships a major release of IOS -- currently it is shipping IOS 12.4 -- every two years.

JUNOS 9.0 runs on Juniper's MX-series Carrier Ethernet switches, M- and T-series routers, EX enterprise LAN switches, J-series branch office routers, and the new Juniper Control System 1200. The NetScreen ScreenOS operating system continues to be offered separately from JUNOS, however, as does the JUNOSe operating system for the company's E-series edge routers, obtained via the acquisition of Unisphere six years ago.

"The E-series does not run the same exact JUNOS that the rest of the core and edge and Carrier Ethernet routers run," says Glen Hunt, a carrier infrastructure analyst at Current Analysis. There are differences between the functions and feature sets of JUNOS and JUNOSe that lead to operational inconsistencies between the platforms, he says.

As Juniper continues to grow, broaden into new markets and acquire companies, it appears that its single-operating-system strategy will continue to be just that -- more strategy than reality, a continually moving target.

"We will look at entering adjacencies in the marketplace," Arnard says. "In which case, be it an acquisition or be it a product, we will make a decision. But our long-term discipline is to be focused on a single network-operating-system of choice, and that is JUNOS."