Network slicing technology is defined as one of the main components of the fifth generation of mobile communications, capable of solving the problem of the colossal growth of data traffic in cellular networks. A key feature of slicing that limits the impact of one slice on another is to provide isolated performance guarantees to deliver high quality of service. In this article, a model of resource allocation during slicing is developed using the queuing theory. The main task of the work is to determine how network resources should be fairly shared between two slices in the system. The resource allocation problem is formulated as an optimization problem. For the constructed model, a numerical analysis was carried out showing the significant effect of the isolation parameters on the performance characteristics of the system. © 2020 Federal Research Center "Computer Science and Control" of Russian Academy of Sciences. All rights reserved.