121 MultiNets: A System for Real-Time Switching between Multiple Network Interfaces on Mobile Devices SHAHRIAR NIRJON, University of Virginia ANGELA NICOARA, CHENG-HSIN HSU, and JATINDER PAL SINGH, Deutsche Telekom Innovation Laboratories USA JOHN A. STANKOVIC, University of Virginia MultiNets is a system supporting seamless switch-over between wireless interfaces on mobile devices in real-time. MultiNets is configurable to run in three different modes: (i) Energy Saving mode–for choosing the interface that saves the most energy based on the condition of the device, (ii) Offload mode–for offloading data traffic from the cellular to WiFi network, and (iii) Performance mode–for selecting the network for the fastest data connectivity. MultiNets also provides a powerful API that gives the application developers: (i) the choice to select a network interface to communicate with a specific server, and (ii) the ability to simultaneously transfer data over multiple network interfaces. MultiNets is modular, easily integrable, lightweight, and applicable to various mobile operating systems. We implement MultiNets on Android devices as a show case. MultiNets does not require any extra support from the network infrastructure and runs existing applications transparently. To evaluate MultiNets, we first collect data traces from 13 actual Android smartphone users over three months. We then use the collected traces to show that, by automatically switching to WiFi whenever it is available, MultiNets can offload on average 79.82% of the data traffic. We also illustrate that, by optimally switching between the interfaces, MultiNets can save on average 21.14 KJ of energy per day, which is equivalent to 27.4% of the daily energy usage. Using our API, we demonstrate that a video streaming application achieves 43–271% higher streaming rate when concurrently using WiFi and 3G interfaces. We deploy MultiNets in a real-world scenario and our experimental results show that depending on the user requirements, it outperforms the state-of-the-art Android system either by saving up to 33.75% energy, achieving near-optimal offloading, or achieving near-optimal throughput while substantially reducing TCP interruptions due to switching. Categories and Subject Descriptors: D.4.7 [Operating Systems]: Organization and Design General Terms: Design, Experimentation, Performance Additional Key Words and Phrases: WiFi, 3G, energy, offload, multiple interfaces ACM Reference Format: Shahriar Nirjon, Angela Nicoara, Cheng-Hsin Hsu, Jatinder Pal Singh, and John A. Stankovic. 2014. MultiNets: A system for real-time switching between multiple network interfaces on mobile devices. ACM Trans. Embedd. Comput. Syst. 13, 4s, Article 121 (March 2014), 25 pages. DOI: http://dx.doi.org/10.1145/2489788 C.-H. Hsu is currently affiliated with National Tsing Hua University. J. P. Singh is currently affiliated with Stanford University. S. Nirjon and J. A. Stankovic were funded, in part, by NSF grants EECS-1035303 and EECS-0901686. Authors’ addresses: S. Nirjon and J. A. Stankovic, Department of Computer Science, University of Virginia; A. Nicoara, Silicon Valley Innovation Center, Deutsche Telekom Innovation Laboratories USA; C.-H. Hsu, Department of Computer Science, National Tsing Hua University; J. P. Singh, Department of Electrical Engineering, Stanford University. Correspondence email: smn8z@virginia.edu. Permission to make digital or hard copies of part or all of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies show this notice on the first page or initial screen of a display along with the full citation. Copyrights for components of this work owned by others than ACM must be honored. Abstracting with credit is permitted. To copy otherwise, to republish, to post on servers, to redistribute to lists, or to use any component of this work in other works requires prior specific permission and/or a fee. Request permissions from permissions@acm.org. c  2014 ACM 1539-9087/2014/03-ART121 $15.00 DOI: http://dx.doi.org/10.1145/2489788 ACM Transactions on Embedded Computing Systems, Vol. 13, No. 4s, Article 121, Publication date: March 2014.