  Developing specialized cloud-based and open-source testbeds is a practical
approach to investigate network slicing functionalities in the fifth-generation
(5G) mobile networks. This paper provides a comprehensive review of most of the
existing cost-efficient and small-scale testbeds that partially or fully deploy
network slicing. First, we present relevant software packages for the three
main functional blocks of the ETSI NFV MANO framework and for emulating the
access and core network domains. Second, we define primary and secondary design
criteria for deploying network slicing testbeds. These design criteria are
later used for comparison between the testbeds. Third, we present the
state-of-the-art testbeds, including their design objectives, key technologies,
network slicing deployment, and experiments. Next, we evaluate the testbeds
according to the defined design criteria and present an in-depth summary table.
This assessment concludes with the superiority of some of them over the rest
and the most dominant software packages satisfying the ETSI NFV MANO framework.
Finally, challenges, potential solutions, and future works of network slicing
testbeds are discussed.
