Research On Virtual-time-based Reproducible Network Emulation Technology

Reproducing network emulation experiments on diverse physical platforms with varying computation and communication resources is non-trivial.Many state-of-the-art network emulation testbeds do not guarantee timing fidelity.Consequently,results obtained from these testbeds can be misleading,especially when insufficient physical resources are provided to run the experiments.Reproducibility is far from being the norm.In this thesis,a novel approach is presented,which can guarantee reproducible results for network emulation.In this thesis,a prototype system is developed,which takes advantage of both time dilation and carefully controlled scheduling of the virtual machines.Time dilation allows sufficiently scaled resources to run the experiments in virtual time,and controlled VM scheduling prescribes the precise timing of message passing for distributed applications—independent of the resource provisioning of the underlying physical testbed.Preliminary experiments show that the prototype system can guarantee reproducible results with varying time dilation,resource subscription,and VM scheduling scenarios.The main contents of this thesis are as follows:Firstly,aiming at the problems of the lack of emulation fidelity and reproducibility under the case of resource oversubscription,which are the limitations of various existing network emulation solutions,in this thesis,a reproducible container-based and virtual-time-based network emulation system design with correct topology mapping and experiment configuration for reproducibility is proposed.Specifically,it takes advantage of virtual time dilation technologies to scale the limited computational and network resources,modeling is made between the virtual emulation network and the testbed for mapping virtual networks among physical machines.Further,the performance and resource(CPU,I/O and network resources)subscription conditions for reproducibility of network emulation is abstracted and summarized,so that the mappings and configurations must be configured accordingly.The reproducible conditions of network emulation are mainly transformed into constraints including three aspects of resource subscription:Nodal Processing Condition" Packet Processing Condition,and Network Traffic Condition.With the optimized solution of these constraints,we get virtual time dialtion configurations and the topology mappings of the emulation networks,which has laid the foundation for-the entire reproducible network emulation technology.Secondly,aiming at another limitation of current containerized network emulation tools,which is the lack of large-scale concurrency ability.The default process scheduler of the Linux system kernel works in a preemptive and best-effort way,which may lead to concurrent container processes not to be scheduled and executed in time,and the time of network transactions(data packets sending and receiving)is confusing due to imprecise scheduling.At the same time,this research also addresses the problem of time synchronization and coordination between different virtual machine with different virtual time dilation configurations among different machines.In this thesis,a virtual-time-based container scheduling synchronization mechanism to coordinately control the virtual time of all virtual machines to advance in unison is proposed,which also strictly controlls the concurrencies of VMs by calculating the scheduling interval to accurately configure the network data packet communication delay between VMs.This which will solve the problem of inaccurate timing series of network data packet sending and receiving caused by untimely concurrency.A Round-Robin polling scheduling policy is designed with strict sequence of virtual machines.On the basis of fully controlling the scheduling procedure,the data communication between VMs is processed with a certain calculated value of delay,which will ensure the high accuracy of the virtual link delay between the VMs to guarantee the reproducibility of network emulation.During the process of implementing the prototype of the network emulation system,this research has made corresponding simple modifications and extensions to the open source code of the Mininet emulation tool,which is convenient for testing and experimenting.