Performability of Service Chains With Rejuvenation: A Multidimensional Universal Generating Function Approach

Network Function Virtualization (NFV) converts legacy telecommunication systems into modular software appliances, known as service chains, running on the cloud. To address potential software aging-related issues, rejuvenation is often employed to clean up their state and maximize performance and availability. In this work, we propose a framework to model the performability of service chains with rejuvenation. Performance modeling uses queueing theory, specifically adopting an $M/G/m$ model with the Allen-Cunneen approximation, to capture real-world aspects related to service times. Availability modeling is addressed through the Multidimensional Universal Generating Function (MUGF), a recent technique that achieves computational efficiency when dealing with systems with many sub-elements, particularly useful for multi-provider service chains. Additionally, we deploy an experimental testbed based on the Open5GS service chain, to estimate key performance and availability parameters. Supported by experimental results, we evaluate the impact of rejuvenation on the performability of the Open5GS service chain. The numerical analysis shows that i) the configuration of replicas across nodes is important to meet availability goals; ii) rejuvenation can bring one additional “nine” of availability, depending on the time to recovery; and iii) MUGF can significantly reduce computational complexity through straightforward algebraic manipulations.