Rajesh Mahindra

NVS: a substrate for virtualizing wireless resources in cellular networks

This paper describes the design and implementation of a network virtualization substrate (NVS ) for effective virtualization of wireless resources in cellular networks. Virtualization fosters the realization of several interesting deployment scenarios such as customized virtual networks, virtual services, and wide-area corporate networks, with diverse performance objectives. In virtualizing a base stations uplink and downlink resources into slices, \ssr NVS meets three key requirements-isolation, customization, and efficient resource utilization-using two novel features: 1) NVS introduces a provably optimal slice scheduler that allows existence of slices with bandwidth-based and resource-based reservations simultaneously; and 2) NVS includes a generic framework for efficiently enabling customized flow scheduling within the base station on a per-slice basis. Through a prototype implementation and detailed evaluation on a WiMAX testbed, we demonstrate the efficacy of \ssr NVS. For instance, we show for both downlink and uplink directions that \ssr NVS can run different flow schedulers in different slices, run different slices simultaneously with different types of reservations, and perform slice-specific application optimizations for providing customized services.

Radio access network virtualization for future mobile carrier networks

This article presents a survey of cellular network sharing, which is a key building block for virtualizing future mobile carrier networks in order to address the explosive capacity demand of mobile traffic, and reduce the CAPEX and OPEX burden faced by operators to handle this demand. We start by reviewing the 3GPP network sharing standardized functionality followed by a discussion on emerging business models calling for additional features. Then an overview of the RAN sharing enhancements currently being considered by the 3GPP RSE Study Item is presented. Based on the developing network sharing needs, a summary of the state of the art of mobile carrier network virtualization is provided, encompassing RAN sharing as well as a higher level of base station programmability and customization for the sharing entities. As an example of RAN virtualization techniques feasibility, a solution based on spectrum sharing is presented: the network virtualization substrate (NVS), which can be natively implemented in base stations. NVS performance is evaluated in an LTE network by means of simulation, showing that it can meet the needs of future virtualized mobile carrier networks in terms of isolation, utilization, and customization.

A scheduling framework for adaptive video delivery over cellular networks

As the growth of mobile video traffic outpaces that of cellular network speed, industry is adopting HTTP-based adaptive video streaming technology which enables dynamic adaptation of video bit-rates to match changing network conditions. However, recent measurement studies have observed problems in fairness, stability, and efficiency of resource utilization when multiple adaptive video flows compete for bandwidth on a shared wired link. Through experiments and simulations, we confirm that such undesirable behavior manifests itself in cellular networks as well. To overcome these problems, we design an in-network resource management framework, AVIS, that schedules HTTP-based adaptive video flows on cellular networks. AVIS effectively manages the resources of a cellular base station across adaptive video flows. AVIS also provides a framework for mobile operators to achieve a desired balance between optimal resource allocation and user quality of experience. AVIS has three key differentiating features: (1) It optimally computes the bit-rate allocation for each user, (2) It includes a scheduler and per-flow shapers to enforce bit-rate stability of each flow and (3) It leverages the resource virtualization technique to separate resource management of adaptive video flows from regular video flows. We implement a prototype system of AVIS and evaluate it on both a WiMAX network testbed and a LTE system simulator to show its efficacy and scalability.

NVS: a virtualization substrate for WiMAX networks

This paper describes the design and implementation of a network virtualization substrate NVS) for effective virtualization of wireless resources in WiMAX networks. Virtualization fosters the realization of several interesting deployment scenarios such as customized virtual networks, virtual services and wide-area corporate networks, with diverse performance objectives. In virtualizing a basestations uplink and downlink resources into slices, NVS meets three key requirements - isolation, customization, and efficient resource utilization - using two novel features: (1) NVS introduces a provably-optimal slice scheduler that allows existence of slices with bandwidth-based and resource-based reservations simultaneously, and (2) NVS includes a generic framework for efficiently enabling customized flow scheduling within the basestation on a per-slice basis. Through a prototype implementation and detailed evaluation on a WiMAX testbed, we demonstrate the efficacy of NVS. For instance, we show for both downlink and uplink directions that NVS can run different flow schedulers in different slices, run different slices simultaneously with different types of reservations, and perform slice-specific application optimizations for providing customized services.

A practical traffic management system for integrated LTE-WiFi networks

Mobile operators are leveraging WiFi to relieve the pressure posed on their networks by the surging bandwidth demand of applications. However, operators often lack intelligent mechanisms to control the way users access their WiFi networks. This lack of sophisticated control creates poor network utilization, which in turn degrades the quality of experience (QoE). To meet user traffic demands, it is evident that operators need solutions that optimally balance user traffic across cellular and WiFi networks. Motivated by the lack of practical solutions in this space, we design and implement ATOM - an end-to-end system for adaptive traffic offloading for WiFi-LTE deployments. ATOM has two novel components: (i) A network interface selection algorithm that maps user traffic across WiFi and LTE to optimize user QoE and (ii) an interface switching service that seamlessly re-directs ongoing user sessions in a cost-effective and standards-compatible manner. Our evaluations on a real LTE-WiFi testbed using YouTube traffic reveals that ATOM reduces video stalls by 3-4 times compared to naive solutions.

Space Versus Time Separation for Wireless Virtualization on an Indoor Grid

The decreasing cost of wireless hardware and ever increasing number of wireless testbeds has led to a shift in the protocol evaluation paradigm from simulations towards emulation. In addition, with a large number of users demanding experimental resources and lack of space and time for deploying more hardware, fair resource sharing among independent co-existing experiments is important. We study the proposed approaches to wireless virtualization with a focus on schemes conserving wireless channels rather than nodes. Our detailed comparison reveals that while experiments sharing a channel by space separation achieve better efficiency than those relying on time separation of a channel, the isolation between experiments in both cases is comparable. We propose and implement a policy manager to alleviate the isolation problem and suggest scenarios in which either of the schemes would provide a suitable virtualization solution.

On 60 GHz wireless link performance in indoor environments

The multi-Gbps throughput potential of 60 GHz wireless interfaces make them an attractive technology for next-generation gigabit WLANs. For increased coverage, and improved resilience to human-body blockage, beamsteering with high-gain directional antennas is emerging to be an integral part of 60 GHz radios. However, the real-world performance of these state-of-the-art radios in typical indoor environments has not previously been explored well in open literature. To this end, in this paper, we address the following open questions: how do these radios perform in indoor line-of-sight(LOS) and non-line-of-sight (NLOS) locations? how sensitive is performance to factors such as node orientation or placement? how robust is performance to human-body blockage and mobility? Our measurement results from a real office setting, using a first-of-its-kind experimental platform (called Presto), show that, contrary to conventional perception, state-of-the-art 60 GHz radios perform well even in NLOS locations, in the presence of human-body blockage and LOS mobility. While their performance is affected by node (or more precisely, antenna array) orientation, simply using a few more antenna arrays and dynamically selecting amongst them shows potential to address this issue. The implications of these observations is in lowering the barriers to their adoption in next-generation gigabit WLANs.

Radio Access Network sharing in cellular networks

Mobile operators are witnessing a dramatic increase in traffic spurred by a combination of popularity of smartphones, innovative applications and diverse services. As mobile traffic transitions from being voice dominated to video and data dominated, the revenue per byte for the mobile operators is declining at an unhealthy rate. To counter the traffic growth and build cost-effective networks, many operators are now forging alliances for RAN (Radio Access Network) sharing to improve coverage and capacity at reasonable investments and operational costs. This paper presents the design and implementation of NetShare, a network-wide radio resource management framework that provides effective RAN Sharing. NetShare introduces a novel two-level scheduler split between the mobile gateway and the cellular basestations to effectively manage and allocate the wireless resources of the radio access network composed of multiple basestations among multiple different entities (such as operators, content providers, etc.) that share the network. Firstly, NetShare provides performance isolation across entities with a minimum guaranteed resource allocation to each entity across the network. Secondly, NetShare optimally distributes the resources to each entity across the network proportional to the resource demand at each basestation. Through extensive LTE-based system simulations and prototype evaluations on a WiMAX testbed, we show the efficacy of NetShare in (a) providing isolation across entities and (b) efficiently distributing resources for each entity across the network thus achieving high utilization of resources for an entity.

Scaling the LTE control-plane for future mobile access

In addition to growth of data traffic, mobile networks are bracing for a significant rise in the control-plane signaling. While a complete re-design of the network to overcome inefficiencies may help alleviate the effects of signaling, our goal is to improve the design of the current platform to better manage the signaling. To meet our goal, we combine two key trends. Firstly, mobile operators are keen to transform their networks with the adoption of Network Function Virtualization (NFV) to ensure economies of scales. Secondly, growing popularity of cloud computing has led to advances in distributed systems. In bringing these trends together, we solve several challenges specific to the context of telecom networks. We present SCALE - A framework for effectively virtualizing the MME (Mobility Management Entity), a key control-plane element in LTE. SCALE is fully compatible with the 3GPP protocols, ensuring that it can be readily deployed in todays networks. SCALE enables (i) computational scaling with load and number of devices, and (ii) computational multiplexing across data centers, thereby reducing both, the latencies for control-plane processing, and the VM provisioning costs. Using an LTE prototype implementation and large-scale simulations, we show the efficacy of SCALE.

Implication of MAC Frame Aggregation on Empirical Wireless Experimentation

Wireless network emulator testbeds have become increasingly important for realistic, at-scale experimental evaluation of new network architectures and protocols. Typically, wireless network performance measurements are made at multiple layers of the wireless protocol stack, i.e. link layer, MAC layer and network layer. This study highlights the impact of layer 2 frame aggregation that is enabled by default in the software drivers for commodity wireless 802.11 devices while it is still not a part of the core 802.11 standard. Using experimental measurements, it is shown that this feature has an impact across a diverse set of wireless experiments and should be considered while comparing results. Measurements on the ORBIT testbed show that throughput measurements can vary up to a startling 25% for certain packet sizes and the variance in receiver side inter-frame delays can almost double if MAC aggregation and preset transmission opportunities are not taken into consideration. Further results for VoIP traffic show a deterioration in jitter of up to 8 times when coupled with MAC layer aggregation in 802.11.