  This paper presents the design and architecture of a network emulator whose
links' parameters (such as delay and bandwidth) vary at different time
instances. The emulator can thus be used in order to test and evaluate novel
solutions for such networks, before their final deployment. To achieve this
goal, different existing technologies are carefully combined to emulate link
dynamicity, automatic traffic generation, and overall network device emulation.
The emulator takes as an input a formal model of the network to emulate and
configures all required software to execute live software instances of the
desired network components, in the requested topology. We devote our study to
the so-called dynamic link networks, with potentially asymmetric links. Since
emulating asymmetric dynamic links is far from trivial (even with the existing
state-of-the-art tools), we provide a detailed design architecture that allows
this. As a case study, a satellite network emulation is presented. Experimental
results show the precision of our dynamic assignments and the overall
flexibility of the proposed solution.
