4. Traffic Flows Supported by RPL

RPL supports three basic traffic flows: multipoint-to-point (MP2P), point-to-multipoint (P2MP), and point-to-point (P2P).

4.1. Multipoint-to-Point Traffic

Multipoint-to-point (MP2P) is a dominant traffic flow in many LLN applications ([RFC5867], [RFC5826], [RFC5673], and [RFC5548]). The destinations of MP2P flows are designated nodes that have some application significance, such as providing connectivity to the larger Internet or core private IP network. RPL supports MP2P traffic by allowing MP2P destinations to be reached via DODAG roots.

4.2. Point-to-Multipoint Traffic

Point-to-multipoint (P2MP) is a traffic pattern required by several LLN applications ([RFC5867], [RFC5826], [RFC5673], and [RFC5548]). RPL supports P2MP traffic by using a destination advertisement mechanism that provisions Down routes toward destinations (prefixes, addresses, or multicast groups), and away from roots. Destination advertisements can update routing tables as the underlying DODAG topology changes.

4.3. Point-to-Point Traffic

RPL DODAGs provide a basic structure for point-to-point (P2P) traffic. For a RPL network to support P2P traffic, a root must be able to route packets to a destination. Nodes within the network may also have routing tables to destinations. A packet flows towards a root until it reaches an ancestor that has a known route to the destination. As pointed out later in this document, in the most constrained case (when nodes cannot store routes), that common ancestor may be the DODAG root. In other cases, it may be a node closer to both the source and destination.

RPL also supports the case where a P2P destination is a 'one-hop' neighbor.

RPL neither specifies nor precludes additional mechanisms for computing and installing potentially more optimal routes to support arbitrary P2P traffic.