Juniper Networks ( JNPR) is set to deliver solid Internet gear sales, but that may not be enough to overcome signs of slippage at its Net security unit. The Sunnyvale, Calif., tech shop will present third-quarter earnings after the close Wednesday. While most investors are expecting the 12th straight quarter of better-than-expected results, some worrywarts find themselves feeling a little insecure about the security business. Juniper has emerged as one of the few upstart success stories in the networking industry. As a top supplier to the telcos' continually strong demand for Internet infrastructure like routers, or boxes that direct data traffic, Juniper has enjoyed three years of surprising growth. But that streak can't go on forever, say analysts. And the day the orders pace slows down, Juniper will have few places to turn to as it looks for new growth. The $3.3 billion acquisition of network defense specialist Netscreen last year was supposed to provide a potential solution to that problem. The computer networking security outfit gave Juniper a new line of gear to sell, and a new market to sell it to. So far though, the Netscreen investment hasn't exactly paid off. Among the setbacks have been the departure of Netscreen CEO Robert Thomas, who was expected to run Juniper's security business. But analysts say cracking the security market and the so-called enterprise market is no easy feat, particularly for a smaller equipment company like Juniper vying with Cisco Systems ( CSCO), which controls up to 80% of some categories. "They have some leading products, but it's a problem of how they can build on that momentum in the enterprise market," says Mark Seery, an analyst with Ovum, an industry research shop.