Process control network security concerns and remedies

Network security for computing platforms connected to corporate networks has been of paramount importance for decades and many hardware and software solutions have evolved to service these needs. Historically, the networks used in process control systems have relied on physical isolation or separation from outside influence to protect their security domain. Several technology driven forces have given rise to a requirement of connecting the formerly isolated process network to the corporate business LAN, Internet or WAN, and other "un-trusted" networks. This paper addresses the issue that physical separation is no longer an acceptable security solution and attempts to answer the question: How do we safely connect the process network to the outside world without risk to the manufacturing process?