IPv6 Multicast Forwarding in RPL-Based Wireless Sensor Networks

Abstract

In wireless sensor deployments, network layer multicast can be used to improve the bandwidth and energy efficiency for a variety of applications, such as service discovery or network management. However, despite efforts to adopt IPv6 in networks of constrained devices, multicast has been somewhat overlooked. The Multicast Forwarding Using Trickle (Trickle Multicast) internet draft is one of the most noteworthy efforts. The specification of the IPv6 Routing Protocol for Low power and Lossy Networks (RPL) also attempts to address the area but leaves many questions unanswered. In this paper we highlight our concerns about both these approaches. Subsequently, we present our alternative mechanism, called Stateless Multicast RPL Forwarding algorithm (SMRF), which addresses the aforementioned drawbacks. Having extended the TCP/IP engine of the Contiki embedded operating system to support both Trickle Multicast (TM) and SMRF, we present an in-depth comparison, backed by simulated evaluation as well as by experiments conducted on a multi-hop hardware testbed. Results demonstrate that SMRF achieves significant delay and energy efficiency improvements at the cost of a small increase in packet loss. The outcome of our hardware experiments show that simulation results were realistic. Lastly, we evaluate both algorithms in terms of code size and memory requirements, highlighting SMRF's low implementation complexity. Both implementations have been made available to the community for adoption.

BMFA: Bi-Directional Multicast Forwarding Algorithm for RPL-based 6LoWPANs

“…More specifically, our results show that BMFA outperforms TM, in terms of reducing the end-to-end delay, design complexity, code size and energy consumption, while on the other hand, TM severely outperforms BMFA in terms of reliability. Finally, note that as documented in [6,7], the performance of multicast forwarding for all engines discussed in this paper is heavily dependent on the underlying MAC layer. For a more detailed description of possible optimizations see [6,7].…”

“…SMRF [6,7] is a multicast forwarding algorithm based on the topology information provided by RPL. Nodes participating in an RPL network exchange topology information in order to build a Destination Oriented Directed Acyclic Graph (DODAG) and construct their routing tables.…”

“…SMRF is very lightweight but this comes at the cost of a severe limitation: it is only capable of forwarding traffic "downwards" in the RPL DODAG tree [6,7]. In this paper, we present a multicast forwarding algorithm called BFMA, an extended version of SMRF scheme.…”

“…We investigate network delay as a factor of traffic bit rate and network density (defined in [7]). As can be observed from Fig.…”

“…Moreover, end-to-end delay is expected to be lower as Imin decreases, while our simulation results present the opposite. Lastly, high delays were anticipated under TM since it uses link layer broadcasts, which are fundamentally inefficient under ContikiMAC, as demonstrated in [7]. On the other hand, when using BMFA in low-density topologies (i.e., up to 0.35), the end-to-end delay declines slightly as the inter-packet delay increases, while when the bit rate decreases (Variable Bit Rate with 1 − 2s inter-packet delay) overall delay reaches its maximum.…”