Mohammad Sajjad Hossain

Aveksha: a hardware-software approach for non-intrusive tracing and profiling of wireless embedded systems

It is important to get an idea of the events occurring in an embedded wireless node when it is deployed in the field, away from the convenience of an interactive debugger. Such visibility can be useful for post-deployment testing, replay-based debugging, and for performance and energy profiling of various software components. Prior software-based solutions to address this problem have incurred high execution overhead and intrusiveness. The intrusiveness changes the intrinsic timing behavior of the application, thereby reducing the fidelity of the collected profile. Prior hardware-based solutions have involved the use of dedicated ASICs or other tightly coupled changes to the embedded nodes processor, which significantly limits their applicability. In this paper, we present Aveksha, a hardware-software approach for achieving the above goals in a non-intrusive manner. Our approach is based on the key insight that most embedded processors have an on-chip debug module (which has traditionally been used for interactive debugging) that provides significant visibility into the internal state of the processor. We design a debug board that interfaces with the on-chip debug module of an embedded nodes processor through the JTAG port and provides three modes of event logging and tracing: breakpoint, watchpoint, and program counter polling. Using expressive triggers that the on-chip debug module supports, Aveksha can watch for, and record, a variety of programmable events of interest. A key feature of Aveksha is that the target processor does not have to be stopped during event logging (in the last two of the three modes), subject to a limit on the rate at which logged events occur. Aveksha also performs power monitoring of the embedded wireless node and, importantly, enables power consumption data to be correlated to events of interest. Aveksha is an operating system-agnostic solution. We demonstrate its functionality and performance using three applications running on Telos motes; two in TinyOS and one in Contiki. We show that Aveksha can trace tasks and other generic events at the function and task-level granularity. We also describe how we used Aveksha to find a subtle bug in the TinyOS low power listening protocol.

Backpacking: Energy-Efficient Deployment of Heterogeneous Radios in Multi-Radio High-Data-Rate Wireless Sensor Networks

The early success of wireless sensor networks has led to a new generation of increasingly sophisticated sensor network applications, such as HPs CeNSE. These applications demand high network throughput that easily exceeds the capability of the low-power 802.15.4 radios most commonly used in todays sensor nodes. To address this issue, this paper investigates an energy-efficient approach to supplementing an 802.15.4-based wireless sensor network with high bandwidth, high power, longer range radios, such as 802.11. Exploiting a key observation that the high-bandwidth radio achieves low energy consumption per bit of transmitted data due to its inherent transmission efficiency, we propose a hybrid network architecture that utilizes an optimal density of dual-radio (802.15.4 and 802.11) nodes to augment a sensor network having only 802.15.4 radios. We present a cross-layer mathematical model to calculate this optimal density, which strikes a delicate balance between the low energy consumption per transmitted bit of the high-bandwidth radio and low sleep power of the 802.15.4. Experimental results obtained using a wireless sensor network testbed reveal that our architecture improves the average energy per bit, time elapsed before the first node drains its battery, time elapsed before half of the nodes drain their batteries, and end-to-end delay by significant margins compared with a network having only 802.15.4.

Backpacking: Deployment of Heterogeneous Radios in High Data Rate Sensor Networks

The early success of wireless sensor networks has led to a new generation of increasingly sophisticated sensor network applications, such as HPs CeNSE. These applications demand high network throughput that easily exceeds the capability of low-power 802.15.4 radios that are most commonly used in todays sensor nodes. To address this issue, this paper investigates an energy-efficient approach to supplementing an 802.15.4 based sensor network with high bandwidth, high power, longer range radios such as 802.11. Exploiting a key observation that the high bandwidth radio achieves low energy consumption per transmitted bit of data due to its inherent transmission efficiency, we propose a hybrid network architecture that utilizes an optimal density of dual-radio (802.15.4 and 802.11) nodes to augment a sensor network having only 802.15.4 radios. We present a cross-layer mathematical model to calculate this optimal density, which strikes a balance between the low energy per bit of the high-bandwidth radio and the low sleep power of 802.15.4 radio. Experimental results obtained using a wireless testbed reveal that our architecture improves the average energy per bit, the time elapsed before half of the nodes drain their battery, and the end-to-end delay by 62%, 106%, and 73% respectively, compared to a network that uses only 802.15.4 radios.

AEGIS: a lightweight firewall for wireless sensor networks

Firewalls are an essential component in today’s networked computing systems (desktops, laptops, and servers) and provide effective protection against a variety of over-the-network security attacks. With the development of technologies such as IPv6 and 6LoWPAN that pave the way for Internet-connected embedded systems and sensor networks, these devices will soon be subject to (and need to be defended against) similar security threats. As a first step, this paper presents Aegis, a lightweight, rule-based firewall for networked embedded systems such as wireless sensor networks. Aegis is based on a semantically rich, yet simple, rule definition language. In addition, Aegis is highly efficient during operation, runs in a transparent manner from running applications, and is easy to maintain. Experimental results obtained using real sensor nodes and cycle-accurate simulations demonstrate that Aegis successfully performs gatekeeping of a sensor node’s communication traffic in a flexible manner with minimal overheads.

SPI-SNOOPER: a hardware-software approach for transparent network monitoring in wireless sensor networks

The lack of post-deployment visibility into system operation is one of the major challenges in ensuring reliable operation of remotely deployed embedded systems such as wireless sensor nodes. Over the years, many software-based solutions (in the form of debugging tools and protocols) have been proposed for in-situ system monitoring. However, all of them share the trait that the monitoring functionality is implemented as software executing on the same embedded processor that the main application executes on. This is a poor design choice from a reliability perspective. This paper makes the case for a joint hardware-software solution to this problem and advocates the use of a dedicated reliability co-processor that is tasked with monitoring the operation of the embedded system. As an embodiment of this design principle, this paper presents Spi-Snooper, a co-processor augmented hardware platform specifically designed for network monitoring. Spi-Snooper is completely cross-compatible with the Telos wireless sensor nodes from an operational standpoint and is based on a novel hardware architecture that enables transparent snooping of the communication bus between the main processor and the radio of the wireless embedded system. The accompanying software architecture provides a powerful tool for monitoring, logging, and even controlling all the communication that takes place between the main processor and the radio. We present a rigorous evaluation of our prototype and demonstrate its utility using a variety of usage scenarios.

AEGIS: a rule based framework for traffic gatekeeping in wireless sensor networks

Traffic gatekeeping, typically implemented using firewalls, is an essential functionality in todays networked computing systems such as desktop PCs. Traffic gatekeeping provides protection against a variety of over-the-network security attacks and can also be used to implement various communication resource management policies. With the development of technologies such as IPv6 and 6LoWPAN that pave the way for Internet-connected embedded systems and sensor networks, traffic gatekeeping will soon become a must-have for these systems as well. Towards this, we present Aegis, a lightweight, rule-based traffic gatekeeping framework for sensor networks. We present an overview of the Aegis architecture, its implementation, and two usage scenarios.