Building a Test Environment for Emulating Link Characteristics of Disruptive Networks

The rapid evolution of broadband wireless Internet access in the recent years has been accompanied by a plethora of devices and applications that allow mobile users to work remotely or stay in touch with their friends as they go. With the increasing demand for ubiquitous access and the notion of being "always connected", the limitations of today's Internet technologies have become obvious, and various research activities are carried on to re-design aspects of the existing Internet architecture to eventually come to a Future Internet where applications do not suffer from transport protocols that are not able to cope with intermittent connectivity, high delay, and even substantial packet loss. While many clean-slate approaches can use network simulation to validate new protocols, the evaluation of enhancements to existing environments is more difficult. Especially for broadband wireless access involving a complex architecture like the Internet Multimedia Subsystem (IMS) the actual network characteristics cannot be modeled easily. To avoid oversimplification of simulation models, we have developed a tool set to measure some characteristics of a real network path and parameterize a link emulator based on the recorded data. The emulator uses the capabilities of the Linux packet scheduler and its queueing disciplines (qdiscs) to facilitate the evaluation of applications and protocols when facing these network conditions. Our approach enables reproducible tests of application behavior in a lab environment, without the uncertainties of changing conditions in the real world. The emulator was used in a research project to improve existing applications that are run on mobile devices while traveling. To dimension the emulator hardware, we have backed on a preliminary study on the prevalent application protocols being used in the target environment. The results presented here indicate that the Linux packet scheduler can be used to create a simple yet powerful emulation engine for changing network conditions.