publications
publications in reversed chronological order.
2025
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Modeling and Optimizing Dual-Connectivity Activation in Cellular NetworksIEEE Open Journal of the Communications Society - In review, 2025Multi-Radio Dual-Connectivity (MR-DC) provides operational flexibility to mobile network operators by allowing the simultaneous use of spectrum resources from different base stations to serve a user. % and serves as a natural tool during generational rollouts. Although the challenges of distributing traffic over the two connections have been widely studied, there exists no analytical model capturing when MR-DC should be activated to achieve target performance requirements. This continues to be that case even as widely deployed systems tend to use rule-based methods whose parameters require informed methods for tuning. We propose an analytical framework for modeling the PDCP buffer under MR-DC, and tuning MR-DC activation and deactivation thresholds that can optimize general objective functions. We build a Multi-Regime Markov Fluid Queue (MRMFQ) model that captures the state of the PDCP buffer under different threshold policies, wireless link characteristics, and user traffic. We introduce a fast and efficient numerical optimization method that leverages the proposed model. The developed optimization framework can accommodate a wide range of objective functions by determining the optimal MR-DC activation and deactivation thresholds. As an example, we optimize for the average energy consumption of a user while enforcing a constraint on the average PDCP layer delay and demonstrate that the proposed dual-threshold policy for MR-DC activation and deactivation significantly reduces the energy consumption, as well as activation and deactivation frequencies. Our novel approach can help optimize contemporary systems and can be used as a model-based optimization for future software-defined RAN implementations.
2024
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Designing Reliable Virtualized Radio Access NetworksUfuk Usubütün, André Gomes, Shankaranarayanan Puzhavakath Narayanan, Matti Hiltunen, and 1 more authorIn GLOBECOM 2024 - IEEE Global Communications Conference, 2024As virtualization of Radio Access Networks (RAN) gains momentum, understanding the impact of hardware and software disaggregation on resiliency becomes critical to meet the high availability requirements of mobile networks. Our paper presents an analytical model, using continuous time Markov chains, to study the impact of virtualization and disaggregation on RAN availability. Our evaluation, assuming typical parameter value ranges for failure and recovery rates, points to containerized platforms reliability as a constraint on vRAN availability. We also find that with active-passive replication, increasing hardware replication factor beyond 2 may not bring any benefits unless failover times are reduced. We also compare the reliability of centralized and distributed virtualized central units.
2023
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Oblivious Routing Using Learning MethodsIn GLOBECOM 2023 - IEEE Global Communications Conference, 2023Oblivious routing of network traffic uses pre-determined paths that do not change with changing traffic patterns. It has the benefit of using a fixed network configuration while robustly handling a range of varying and unpredictable traffic. Theoretical advances have shown that the benefits of oblivious routing are achievable without compromising much capacity efficiency. For oblivious routing, we only assume knowledge of the ingress/egress capacities of the edge nodes through which traffic enters or leaves the network. All traffic patterns possible subject to the ingress/egress capacity constraints (also known as the hose constraints) are permissible and are to be handled using oblivious routing. We use the widely deployed segment routing method for route control. Furthermore, for ease of deployment and to not deviate too much from conventional shortest path routing, we restrict paths to be 2-segment paths (the composition of two shortest path routed segments). We solve the 2-segment oblivious routing problem for all permissible traffic matrices (which can be infinitely-many). We develop a new adversarial and machine-learning driven approach that uses an iterative gradient descent method to solve the routing problem with worst-case performance guarantees. Additionally, the parallelism involved in descent methods allows this method to scale well with the network size making it amenable for use in practice.
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Do Switches Still Need to Deliver Packets in Sequence? - BEST PAPER AWARDUfuk Usubütün, Fraida Fund, and Shivendra PanwarIn HPSR 2023 - IEEE 24th International Conference on High Performance Switching and Routing, 2023Internet switches become harder and costlier to build for higher line rates and switch capacities. In-sequence delivery of packets has traditionally been a constraint on switch designs because TCP loss detection was considered vulnerable to out-of-sequence arrivals. For this reason, extremely efficient and simple designs, such as the Load Balanced Birkhoff-von Neumann Switch, were considered impractical. However, we reevaluate this constraint considering modern TCP implementations with loss detection algorithms like Recent Acknowledgment (RACK) that are more resilient to out-of-order arrivals. In a set of testbed experiments representative of wide area core networks, we evaluated the performance of TCP flows traversing a load balanced switch that reorders some packets within a flow. We show that widely deployed and standard TCP implementations of the last decade achieve similar performance when traversing a load balanced switch as they do when there is no reordering. Furthermore, we also verified that an increase in the line rate leads to favorable conditions for time based loss detection methods, such as the one used in RACK. Our results, if further validated, suggest that switch designs that were previously thought to be unsuitable can potentially be utilized, thanks to the relaxation of the in-sequence delivery constraint.
