NEST: a network simulation & prototyping testbed

This paper describes Nest, an graphical environment for distributed networked systems simulation and rapid-prototyping. Nest users can develop and test distributed systems and protocols (from crude models to actual system code) within simulated network scenarios. Nest represents an environment-based approach to simulation. Users view Nest as an extension of their standard Unix'"" environment. Nest offers the generality of language-based simulation techniques and the efficiencies of model-based techniques. Users interact with Nest through standardized graphical interfaces. Nest permits the users to modify and reconfigure the simulation during execution. Thus, it is possible to study the dynamic response of a distributed system to failures or burst-loads. Nest is organized as a simulation server, responsible for execution of complex simulation scenarios and client monitors responsible for simulation control. The client/server model permits distribution of Nest over a network environment. This permits migration of simulations to powerful remote computational servers as well as development of a shared multi-site simulationflntegration testbed. Nest is ponable and extensible. It has been ported to virtually all Unix variants and distributed since 1987 to over 150 sites worldwide. It has been used in scores of studies ranging from communication protocols, to distributed databases and operating systems as well as distributed manufacturing systems. * Research supponed by DARPA contract HF-29601-87-C-0074 and by the NY State CAT contract #NYSSlFCA T(89)-5 t UNIX is a trademark of AT&T. Nest pursues a different approach to simulation studies: extending a networked operating system environment to support simulation modeling and efficient execution. This environme1Jl:-based approach to simulation shares with language-based approaches the generality aria modeling power. Nest may be used to model arbitrary distributed interacting systems. Neli also shares with the language-based approach an internal execution architecture (see below) that accomplishes very efficient scheduling of a large number of processes. However. unlike language-based approaches, Nest does not require the user to master or use a new/separate simulation language facility and the processes of design/development and simulation are integrated The user can study the behavior of the actual system being developed (at any level of detail) under arbitrary simulated scenarios. The routing protocol designer. for example, can attach the very routing protocol designed (actual code with minor adjustment) to a Nest simulation and pursue study of the actual system behavior. As the system changes through the design process, new simulation studies may be conducted by attaching the new code to the same simulation models. Nest can thus be used as an integral part of the design process unified with other tools (e.g., for debugging). In similarity to model-based approaches, Nest is specifically targeted towards a limited scope of applications: distributed networked systems. Nest supports a built-in customizable communication network model. However. this scope has been sufficiently broad to support studies ranging from low-level communication protocols to distributed transaction processing systems, avionic systems and even manufacturing processes. The environment-based approach to simulation offers a few important attractions to users: