Jongsoo Jeong

DualMOP-RPL: Supporting Multiple Modes of Downward Routing in a Single RPL Network

RPL is an IPv6 routing protocol for low-power and lossy networks (LLNs) designed to meet the requirements of a wide range of LLN applications including smart grid AMIs, home and building automation, industrial and environmental monitoring, health care, wireless sensor networks, and the Internet of Things (IoT) in general with thousands and millions of nodes interconnected through multihop mesh networks. RPL constructs tree-like routing topology rooted at an LLN border router (LBR) and supports bidirectional IPv6 communication to and from the mesh devices by providing both upward and downward routing over the routing tree. In this article, we focus on the interoperability of downward routing and supporting its two modes of operations (MOPs) defined in the RPL standard (RFC 6550). Specifically, we show that there exists a serious connectivity problem in RPL protocol when two MOPs are mixed within a single network, even for standard-compliant implementations, which may result in network partitions. To address this problem, this article proposes DualMOP-RPL, an enhanced version of RPL, which supports nodes with different MOPs for downward routing to communicate gracefully in a single RPL network while preserving the high bidirectional data delivery performance. DualMOP-RPL allows multiple overlapping RPL networks in the same geographical regions to cooperate as a single densely connected network even if those networks are using different MOPs. This will not only improve the link qualities and routing performances of the networks but also allow for network migrations and alternate routing in the case of LBR failures. We evaluate DualMOP-RPL through extensive simulations and testbed experiments and show that our proposal eliminates all the problems we have identified.

Low-power and topology-free data transfer protocol with synchronous packet transmissions

Tightly synchronizing transmissions of the same packet from different sources theoretically results in constructive interference. Exploiting this property potentially speeds up network-wide packet propagation with minimal latencies. Our empirical results suggest the timing constraints can be relaxed in the real world, especially for radios using lower frequencies such as the IEEE 802.15.4 radios at 900 MHz. Based on these observations we propose PEASST, a topology-free protocol that leverages synchronized transmissions to lower the cost of end-to-end data transfers, and enables multiple traffic flows. In addition, PEASST integrates a receiver-initiated duty-cycling mechanism to further reduce node energy consumption. Results from both our Matlab-based simulations and indoor testbed reveal that PEASST can achieve a packet delivery latency matching the current state-of-the-art schemes that also leverages synchronized transmissions. In addition, PEASST reduces the radio duty-cycling by three-fold. Furthermore, comparisons with a multi-hop routing protocol shows that PEASST effectively reduces the per-packet control overhead. This translates to a ~10% higher packet delivery performance with a duty cycle of less than half.

Improving the Packet Delivery Performance for Concurrent Packet Transmissions in WSNs

In this letter, we investigate the properties of packet collisions in IEEE 802.15.4-based wireless sensor networks when packets with the same content are transmitted concurrently. While the nature of wireless transmissions allows the reception of a packet when the same packet is transmitted at different radios with (near) perfect time synchronization, we find that in practical systems, platform specific characteristics, such as the independence and error of the crystal oscillators, cause packets to collide disruptively when the two signals have similar transmission powers (i.e., differences of <;2 dBm). In such scenarios, the packet reception ratio (PRR) of concurrently transmitted packets falls below 10%. Nevertheless, we empirically show that the packet corruption patterns are easily recoverable using forward error correction schemes and validate this using implementations of RS and convolutional codes. Overall, our results show that using such error correction schemes can increase the PRR by more than four-fold.

Non-invasive rapid and efficient firmware update for wireless sensor networks

To maintain software of sensor nodes in wireless sensor networks efficiently, it is necessary to minimize the size of transferred data in firmware update. We propose a non-invasive rapid and efficient incremental firmware update algorithm called MoRE. In MoRE algorithm, the host transfers only delta, which is the information of different parts between old and new firmware image, to reduce the size of transferred data. The sensor node makes new binary image from its current image and the transferred messages. The MoRE shows comparable performance to previous works without invasive methods. Unlike the previous works, MoRE does not require extra memory for metadata in sensor nodes and does not need to use relocatable code.

Towards full RPL interoperability: addressing the case with downwards routing interoperability

In this work we point out the issue of the IETF RPL routing protocols two different downwards routing schemes not being able to interoperate with each other. This problem is less of an issue when low-power and lossy networks (LLNs) are deployed homogeneously but with the industrial kickoff and large scale deployments, the interoperability of heterogeneous, standards-compliant implementations will become a significant issue. To address this, we suggest two major changes to IETF RPL (RFC 6550). First we suggest that all storing mode nodes should hold the capability to understand and attach source routing headers that the non-storing mode nodes require to forward packets. Next, we suggest that RPLs non-storing mode nodes should send their destination advertisement messages hop-by-hop, rather than the current end-to-end approach. We show, with two different IPv6 implementations in TinyOS and NanoQplus, that our suggestions high achieve high interoperability performance among different implementations for downwards traffic patterns.

An adaptive link management for Vehicular Ad hoc networks

The local information gathered by periodic beacons may include some outdated one caused by high mobility of nodes and the interval of beacons in the Vehicular Ad hoc Networks (VANET). Routing protocols for VANET can eliminate outdated links to neighboring nodes effectively if they can estimate the link expiration time. The transmission range is required to get the link duration time, and the value is not only non-fixed in the presence of signal obstacles but also changed more quickly. It is hard to apply the link time in the environment because of that reason. In this paper, we propose an approach to assign a separated transmission range per road segment, that is, Quasi-Boundary, to solve the limitation. We evaluate the effectiveness of our scheme via network simulations, and the scheme gets higher the end-to-end delivery rate by eliminating outdated information.

Poster: Click based IP border router for low-power and lossy networks

The IETFs new protocols for Low-power and Lossy Networks are delegating their several functions to an IP border router that has more resources than other constrained nodes in the network. It makes the complexity of the IP border router higher than other conventional routers. For this reason, a well-designed platform for routers is important for fast development and easy debugging. In this paper, we check the feasibility of Click Modular Router platform to develop the IP border router for LLNs. Then, we present a design and an implementation of the IP border router on top of Click.