The use of TCP/IP-based communication protocols is not a new development. As the burgeoning success of the Internet attests, TCP/IP usage is widespread. Until now, the use of TCP/IP—particularly over the Internet—has been the domain of large and expensive server systems and resource-rich desktop-client machines. Even the developing market for Internet-enabled handheld computing is based upon powerful processors. Typically, those processors are embedded within devices that carry a price tag of several hundred dollars. Now, TCP/IP-based Internet networking is facing its next big development: the connection of large numbers of embedded systems featuring relatively low processing power. These low-cost embedded systems will use a thin-client model. While communicating over the Internet to central servers, they will perform a wide range of monitoring and control applications.

The benefits of remotely monitoring and controlling embedded systems have been evident for a long time. Yet one simple factor has inhibited the development and deployment of such systems—cost. For connectivity to be incorporated into an embedded system, it must invite benefits that outweigh the cost of its inclusion. For example, efficiency savings could be made possible by remote management or monitoring. Or, manufacturers could benefit from the ability to charge more for the final product, thanks to value-added features made possible by connectivity.

Until recently, the costs associated with incorporating connectivity into a system were high. Typically, no TCP/IP-stack software was available for the small 8- and 16-b microcontrollers used in embedded systems. Even if the software was available, the memory demand was usually prohibitive in both ROM and expensive RAM. Without the ability to 'talk' TCP/IP, companies had to look to proprietary network solutions in order to get their embedded clients connected to their servers. Obviously, the creation of such network infrastructures was difficult and expensive.

Fortunately, this is no longer the situation. Recent developments in software technology have made stacks available for the small, low-cost microcontrollers at the heart of many high-volume embedded systems. In addition, these stacks are ultra efficient. They allow TCP/IP-based systems to be developed for microcontrollers with as little as 16K of ROM and 2K of RAM. TCP/IP is the key that opens the existing Internet infrastructure, enabling it to be used as a network to connect embedded systems to their servers. The possibility of using the ubiquitous Internet as the transmission network removes a major potential barrier to the rollout of connected embedded applications.

With the introduction of TCP/IP-based connectivity into embedded applications, developers may have to get involved in areas of software functionality that they have never tackled. Typically, 'Internet programming' has been the domain of the desktop system programmer rather than the embedded-software engineer. When adding Internet connectivity to a product, it is essential that developers of high-volume, low-cost embedded systems remain true to the 'golden rules' of embedded-systems programming. Application development should focus on the conservation of scarce resources. Developers must not adopt the 'memory-no-object' style of programming that is prevalent among creators of desktop software applications.

To select an off-the-shelf TCP/IP solution for use in such systems, look at the credentials of the supplier as an embedded-systems solution provider. Do not think in terms of a networking or desktop pedigree. For embedded systems, there is little value in taking a UNIX-style TCP/IP stack and attempting to slim it down to fit the available resources. Such a choice will not meet the cost constraints that are inherent in high-volume deployments. It is best if the stack has been developed from scratch to meet the requirements of the applicable RFCs using sound embedded-engineering principles.

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Most applications that involve low-cost embedded systems communicating via TCP/IP will be designed to use the thin-client model. This model partitions the functionality of the application across one or many embedded systems and a number of desktop servers. To optimize the efficiency of the application, the system developer can therefore make best use of the available computing resources. Though such a concept may be new to embedded-systems developers, it has the potential to reduce the cost of a product while adding value to it.

When considering the thin-client model, the designer will need to evaluate the available system resources at both the embedded and server ends. The model enables designers to distribute resources. Through analysis, they also can focus on what can be implemented more effectively at either end. The resources required by each application will vary, but there are some key questions to consider: Can data storage and access be handled more effectively on a larger computer (server) rather than an embedded controller? What is the cost per byte to store large amounts of data? Will it be cheaper on a disk drive versus integrated-circuit memory? Also, can application management, data gathering, and dissemination be performed more efficiently via centralized storage?

Many factors affect the selection of connection hardware. The designer should consider what hardware is available locally at the embedded end. For example, if Ethernet is available with an Internet gateway, it could be used to connect to the Internet. As always, security is an issue. Invariably, various levels of security can be implemented in different ways. In some cases, higher levels of security will be more suited to implementation on a larger computer, which also acts as the centralized data store.