Case study: Ruggedizing Cisco Ethernet switches for the military
To meet the military’s requirements for computing technologies that are cost sensitive yet extremely rugged, commercial products can be enhanced for harsh-use applications. The following case study describes how the Cisco IE-3000 switch was ruggedized for use in demanding military IP networking applications.
With military customers seeking the most robust yet economical computing systems, a “ruggedized” commercial product can often be the best solution to meet the needs of a specific military application. The terms “rugged” and “ruggedized” are often used to describe electronics capable of enduring harsh environments; however, there is a strong distinction between the two terms that indicates how a product for military use was created.
“Rugged” systems are products that are designed from the ground up to meet the requirements of specific harsh environments. Conversely, the term “ruggedized” refers to a commercial product that was not originally intended for harsh-use application, but was enhanced to endure airborne, ground vehicle, and/or shipboard deployments. The following case study examines how Parvus engineers ruggedized Cisco Systems’ commercial IE-3000 switch for use in demanding military IP networking technology refresh applications.
Cisco dominates military’s networking infrastructure
Cisco CEO John Chambers reported earlier this year to Fox Business that the networking giant has more than 70 percent market share in the public sector. The pervasiveness of Cisco technology and its IOS software in the government arena makes this networking technology an ideal platform for ruggedized products. Additionally, Cisco is credited with helping to define many of today’s networking standards and protocols, actively contributing to the standards committees within the Internet Task Force, IEEE, and other groups. As a consequence, with the government’s widespread adoption of Cisco products and its comprehensive feature set, military contractors are increasingly seeking Cisco-based rugged computing technologies for deployment in tactical military applications onboard air and land vehicles (Figure 1).
From the military’s perspective, adopting ruggedized Cisco switches and networking products provides a cost-effective method for implementing the latest networking technology that meets stringent environmental standards. Also, deploying ruggedized Cisco products reduces time to deployment on the battlefield, as many military personnel are trained to operate Cisco’s network management software.
One of Cisco’s latest Ethernet switches, the IE-3000, recently proved to be an ideal ruggedization candidate for military use, as this switch was designed for industrial Ethernet applications, including factory automation, energy and process control, and Intelligent Transportation Systems (ITSs). As its intended commercial use already exceeded traditional commercial environments, the Cisco IE-3000 switch included extended temperature and enhanced shock/vibration and surge ratings not typically offered by commercial networking gear.
Optimizing the IE-3000 to meet EMI standards
Although the IE-3000 is considerably more rugged than the norm for a commercial product, military-level requirements dictated that engineers further optimize the switch by making mechanical enhancements for ingress protection against dust, water, and EMI (Table 1). The EMI compliance standard required for military use includes MIL-STD-461 for radiated and conducted emissions and radiated and conducted susceptibility.
Ruggedizing the IE-3000 to meet this rugged EMI standard required protection against input voltage inversion, voltage surges, and overvoltage spikes in accordance with MIL-STD-704 and -1275. This was accomplished through the implementation of a reverse voltage/overvoltage protection circuit. Engineers also implemented several improvements, such as designing a sealed enclosure with good EMI gaskets and creating proper test cables. Moreover, proper grounding techniques and good bonding between chassis surfaces were critical in creating an enclosure to act as a faraday cage. Since external power leads are typically unshielded in test and application, they can be the single largest point of noise and susceptibility. By including a well-designed filter at the point where power enters the system, the ruggedized IE-3000 complies with EMI requirements as the filter prevents internal noise from exiting the system and protects sensitive electronics from external noise that otherwise might enter the system.
Connectors and cables: Ensuring stability for possible points of failure
Like many commercial products, the IE-3000 includes RJ-45 network connectors. Although adequate for the IE-3000’s original purposes, these RJ-45 connectors are notoriously prone to failure under extreme vibration and do not provide ingress protection against dust and water. Parvus engineers removed and replaced them with locking headers that ultimately terminated with circular MIL-DTL-38999-style connectors that not only protect against dust, water, vibration, and shock, but also bring ports to the outside world.
Although a cableless design is optimal for rugged conditions, when ruggedizing an existing commercial product that includes cables, not all cables may be eliminated; thus, additional steps need to be taken to ensure stability. Since the IE-3000 contains some cabling, engineers leveraged rigid flex circuits and board-to-board interfaces where possible and implemented cable braiding, tie-downs, and other strain-relief features to maximize reliability and prevent the cables from disconnecting or being severed in vibration or shock.
Ruggedizing components to survive environmental extremes
To further ruggedize the Cisco IE-3000, additional techniques were implemented to stabilize the components during shock and vibration. One such technique includes potting. Potting can be performed by completely encapsulating an electronic device or by staking it down, to provide protection against shock and vibration. For ruggedizing the IE-3000, potting was an essential procedure, as it ensures security of sensitive designs and creates a barrier against moisture, fungus, dust, and corrosion. By enhancing circuit reliability by eliminating leakage from high-voltage circuits, potting protects against voltage arcs and short circuits and prevents the formation of tin whiskers.
Potting materials come in a multitude of varieties, the selection of which is determined by requirements including thermal, outgassing, electrical and thermal isolation or conduction capabilities, and manufacturing application requirements. The selection of the correct potting materials is a key engineering decision as it can determine the proper functioning of system components.
As a final step, engineers applied conformal coating material to the IE-3000’s electronic circuitry to protect it from moisture, dust, chemicals, and temperature extremes. This process improves and extends the working life of the board and helps ensure safety and reliability. These coatings “conform” to the contours of the board and its components, creating a thin protective layer that is both lightweight and flexible. For circuit boards that are not conformal coated, extreme environmental conditions could cause corrosion, mold growth, and current leakage, resulting in board failure. Taking extra precautions to ensure that the board circuitry can endure harsh conditions is paramount in designing and building a ruggedized computing system that will last through the life of the product.
Thermal management techniques ensure rugged performance
With heat issues often credited as the largest contributor to system failures, ruggedizing systems to meet these thermal challenges is a critical step. Thermal management for defense applications has always been a challenge because of the high operating temperatures of the latest processors and dense packaging needed for environmental ruggedness. Cisco’s standard IE-3000 switch relies on internal heat sinks and a vented case with passive airflow through the case to cool the unit. However, relying on convection cooling only inside a completely sealed box would have severe limits, so Parvus incorporated conduction-cooling techniques to maximize the heat transfer, while the unit still remained fanless and passively cooled.
To reduce weight and speed the system’s heat transfer rate, engineers removed all of the standard Cisco finned heat sinks and replaced them with heat spreaders, which are conduction-cooling mechanisms. The inclusion of heat spreaders, thin sheets of metal incorporated on top of a device to help dissipate heat, significantly reduced thermal issues inside the IE-3000. These heat spreaders route heat through an internal rail/truss system that supports all of the circuit card assemblies from shock/vibration and dissipates the heat to the aluminum enclosure that incorporates finning on the outside to maximize surface area for cooling.
Further identifying any potential thermal management issues, engineers used thermal modeling software to analyze potential cooling issues, ensuring the new thermal devices included in the ruggedized Cisco IE-3000 iteration – called the “DuraNET 3000” – would meet specific military standards. Infrared imaging cameras were also used to locate any hot spots or thermal concerns. By running a variety of analyses, engineers quickly determined where potential points of failure could exist when subjected to the extreme temperatures encountered by the military.
Bringing it all together
As evidenced by the creation of the DuraNET 3000, the process of ruggedizing a commercial product for military use is no small feat. However, ruggedized products can take advantage of the technological advancements made by the world’s leading network manufacturers and, when combined with proven ruggedization techniques, offer a robust, cost-effective computing choice engineered to meet today’s military requirements.
Parvus Corporation 801-483-1533 www.parvus.com