Link Emulation on the Data Link Layer in a Linux-based Future Internet Testbed Environment

摘要

Protocol design and development is not a straight-forward process. Each approach must be validated for interactions and side-effects in the existing network environments. But the Internet itself is not a good test environment, since its components are not controllable and certain problem situations (like congestion or error conditions) are difficult to reproduce. Various testbeds have been built up to fill this gap. Most of these testbeds also support link emulation, i.e. using software to mimic the characteristic behaviour of certain kinds of network links (like bandwidth bottlenecks or error-prone radio transmissions). The most popular link emulation systems are the Linux-based NetEm and Dummynet, which are e.g. applied on the IP layer of Planet-Lab and various other testbeds. However, the restriction to the OSI Network Layer (here: IP) is insufficient to test new non-IP Future Internet protocols. In this paper, we first introduce Dummynet and NetEm. After that, we will present our approach of adapting Dummynet for Linux to support link emulation on the Data Link Layer. Finally, we evaluate the applicability and performance of Dummynet and NetEm for link emulation on the Data Link Layer, in a Planet-Lab-based testbed environment. Our goal is to outline the performance and limitations of both approaches in the context of Planet-Lab-based testbeds, in order to make them applicable for the evaluation of non-IP Future Internet protocols.