Communication networks form the basis for supporting various ubiquitous and pervasive Grid applications, therefore network service discovery, selection, and composition play a significant role in ubiquitous and pervasive Grids. Due to the heterogeneity of networking systems in ubiquitous and pervasive computing environments, network service description and discovery in ubiquitous and pervasive Grids face new challenges that require enhancement of current existing Grid service discovery technologies. This paper proposes a new approach for describing service capabilities of network services in ubiquitous and pervasive Grids and develop a technology for discovering network services that meet the performance requirements of Grid applications. The application of network calculus techniques makes the developed technologies independent with the underlying networking platform, thus applicable to heterogeneous network services in ubiquitous and pervasive computing environments. The approach is also scalable to support Grid network service composition.