IPv6 Routing Protocol for Low-Power and Lossy Networks (RPL)

IETF chartered two working groups (WGs) to standardize protocols for constrained networks.

1. 6LoWPAN standardizes the adaptations of IPv6 for networks that use IEEE 802.15.4 PHY layer.
2. Routing over Low-Power and Lossy Links (RoLL) standardizes a link-independent IPv6 routing protocol for resource constrained devices. It defines the RPL routing protocols, which builds a robust topology over lossy links with minimal state requirements.

RoLL studied the routing requirements for a broad range of applications based on more than a decade of research in WSN, and produced four RFCs describing routing in four environments:

1. RFC5548: Routing Requirements for Urban Low-Power and Lossy Networks
2. RFC5673: Industrial Routing Requirements in Low-Power and Lossy Networks
3. RFC5826: Home Automation Routing Requirements in Low-Power and Lossy Networks
4. RFC5867: Building Automation Routing Requirements in Low-Power and Lossy Networks

RoLL targets the network architecture for low-power and lossy network (LLN), which is defined by the following characteristics.

• LLN devices maintain very little state and are optimized for saving energy,
• the traffic patterns in LLN can be more complex than unicast flows,
• the traffic must be carried over links that can forward only small frames.

These characteristics impose unique requirements that make existing routing protocols unsuitable for LLNs. RPL was defined to address this shortcoming. RPL supports 3 traffic patterns: multipoint-to-point (MP2P), point-to-multipoint (P2MP) and point-to-point (P2P). MP2P is currently the dominant traffic type for LLN applications.